STANDARDS AUSTRALIA. Amendment No. 1 to AS Residential timber-framed construction Part 1: Design criteria

Transcription

1 AS /Amdt 1/ STANDARDS AUSTRALIA Amendment No. 1 to AS Residential timber-framed construction Part 1: Design criteria CORRECTION The 1999 edition of AS is amended as follows; the amendments should be inserted in the appropriate places. SUMMARY: This Amendment applies to CONTENTS, Tables and 5.2. Published on 26 February AMDT No. 1 FEB 2002 AMDT No. 1 FEB 2002 AMDT No. 1 FEB Page 3 CONTENTS SECTION 5, delete UPLIT, and replace with UPLIFT. Page 76 Table Last column, last row, delete +0.9 or 1.6, and replace with +0.7 or 1.5. Page 100 Table 5.2 Delete existing Table 5.2, and replace with the following: TABLE 5.2 NET PRESSSURE COEFFICIENTS FOR ROOF UPLIFT Wind classification Tile roof C pt Sheet roof N1 and N N3 and N C1 to C ISBN

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3 AS Residential timber-framed construction Part 1 Design criteria (Incorporating Amendment No.1) S t a n d a r d s Australia

4 This Australian Standard was prepared by Committee TM/1, Timber Structures. It was approved on behalf of the Council of Standards Australia on 10 October 1999 and published on 5 December The following interests are represented on Committee TM/1: Australian Building Codes Board Australian Timber Importers Federation Building Research Association of New Zealand CSIRO, Building, Construction and Engineering Curtin University of Technology Institution of Engineers, Australia Master Builders Australia Monash University New Zealand Forest Research Institute New Zealand Timber Industry Federation New Zealand Timber Suppliers Group Pine Australia Plywood Association of Australia Queensland Forestry Research Institute Timber Research and Development Advisory Council of Queensland University of Technology, Sydney Keeping Standards up-to-date Standards are living documents which reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments which may have been published since the Standard was purchased. Detailed information about Standards can be found by visiting the Standards Australia web site at and looking up the relevant Standard in the on-line catalogue. Alternatively, the printed Catalogue provides information current at 1 January each year, and the monthly magazine, The Australian Standard, has a full listing of revisions and amendments published each month. We also welcome suggestions for improvement in our Standards, and especially encourage readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via at mail@standards.com.au, or write to the Chief Executive, Standards Australia International Ltd, GPO Box 5420, Sydney, NSW This Standard was issued in draft form for comment as DR

5 AS (Incorporating Amendment No. 1) Australian Standard Residential timber-framed construction Part 1: Design criteria First published as AS Reissued incorporating Amendment No. 1 (February 2002). COPYRIGHT Standards Australia International All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher. Published by Standards Australia International Ltd GPO Box 5420, Sydney, NSW 2001, Australia ISBN X

6 AS PREFACE This Standard was prepared by the Joint Standards Australia/Standards New Zealand Committee TM/1, Timber Structures. This Standard incorporates Amendment No. 1 (February 2002). The changes required by the Amendment are indicated in the text by a marginal bar and amendment number against the clause, note, table, figure, or part thereof affected. This Standard is the result of a consensus of representatives on the Joint Committee that it be produced as an Australian Standard. The objective of this Standard is to provide users with the design methods, assumptions and other design criteria, which have been used in the preparation of the Span Tables, uplift forces and racking pressures contained within AS , AS and AS Continued development of timber framing systems and the need to cater for a widening variety of materials and design conditions have led to a total revision of structural framing design. These developments include (a) provision for limit state design methods; (b) revised/new structural grades for timber; (c) provisions catering for open plan living larger spans, wider openings and bigger rooms, which need a more rational approach to bracing design; (d) special engineered and fabricated timber products; (e) recognition of a wider range of high wind and cyclonic design; and (f) computer-aided design software for member sizes, bracing and tie-down. This Standard is a companion publication to the following: AS 1684 Residential timber-framed construction Part 2 Non-cyclonic areas Part 3 Cyclonic areas Part 4 Simplified Non-cyclonic areas The term normative has been used in this Standard to define the application of the appendix to which it applies, A normative appendix is an integral part of a Standard.

7 3 AS CONTENTS Page SECTION 1 SCOPE AND GENERAL 1.1 SCOPE AND APPLICATION REFERENCED DOCUMENTS OTHER METHODS BASIS FOR DESIGN DEFINITIONS NOTATION... 8 SECTION 2 DESIGN OF ROOF MEMBERS 2.1 ROOF BATTENS RAFTERS ROOF BEAMS RIDGE OR INTERMEDIATE BEAMS UNDERPURLINS STRUTTING BEAMS COUNTER STRUTTING BEAMS COMBINED HANGING STRUTTING BEAMS CEILING BATTENS CEILING JOISTS HANGING BEAMS COUNTER BEAMS VERANDAH BEAMS SECTION 3 DESIGN OF WALL MEMBERS 3.1 POSTS LOADBEARING WALL STUDS WALL PLATES FOR LOADBEARING WALLS LINTELS SECTION 4 DESIGN OF FLOOR MEMBERS 4.1 FLOOR JOISTS BEARERS A1 SECTION 5 DETERMINATION OF UPLIFT FORCES 5.1 SCOPE AND GENERAL DETERMINATION OF NET UPLIFT PRESSURES SECTION 6 PRESSURES FOR DETERMINATION OF RACKING FORCES 6.1 SCOPE AND GENERAL EQUIVALENT PRESSURES ON PROJECTED AREAS APPENDICES A CHARACTERISTIC BEAM SHEAR STRENGTHS FOR F-GRADES B WIND CLASSIFICATIONS AND DYNAMIC GUST PRESSURES C DESIGN OF OVERHANGS FOR PARALLEL BIRDSMOUTH NOTCHED RAFTERS

8 AS STANDARDS AUSTRALIA Australian Standard Residential timber-framed construction Part 1: Design criteria SECTION 1 SCOPE AND GENERAL 1.1 SCOPE AND APPLICATION Scope This Standard sets out the design methods, assumptions and other criteria used in the preparation of the Span Tables, uplift forces and racking pressures contained within AS , AS and AS The design criteria apply for the preparation of design data for traditional timber-framed construction where the loading and performance requirements correspond to those for Class 1 and Class 10 buildings as defined by the Building Code of Australia. This Standard should be read in conjunction with AS , AS and AS , the AS 1170 series, and AS NOTE: Whilst this Standard may be used as a reference for the design of Class 10 buildings, less conservative levels of design for this building class may be permitted by building regulations and other Australian Standards Application The design criteria contained herein may be used as a basis for the preparation of Span Tables and design data for structural wood products, having stress grades and sizes other than those included in AS , AS and AS where the application and performance are claimed to be consistent with AS , AS and AS NOTE: The use of the design criteria contained in this Standard may provide evidence of satisfactory safety and serviceability performance. 1.2 REFERENCED DOCUMENTS The following documents are referred to in this Standard: AS 1170 Minimum design loads on structures (known as the SAA Loading Code) Part 1: Dead and live loads and load combinations Part 2: Wind loads Part 3: Snow loads Part 4: Earthquake loads 1684 Residential timber-framed construction Part 2: Non-cyclonic areas Part 3: Cyclonic areas Part 4: Simplified Non-cyclonic areas 1720 Timber structures Part 1: Design methods Standards Australia

9 5 AS AS 4055 Wind loads for housing CSIRO Low-rise domestic and similar framed structures Part 1: Design criteria (revised 1978) 1.3 OTHER METHODS This Standard does not preclude the use of other methods of design, other assumptions or criteria for design or any other means of demonstrating satisfactory safety and serviceability performance. 1.4 BASIS FOR DESIGN General The design criteria contained in this Standard are an interpretation of the AS 1170 series, and AS The criteria have been formulated for the preparation of generalized design data for houses constructed using the traditionally evolved timber framing system as described in AS , AS and AS The design criteria are based upon the assumptions described in Clauses to below Geometric limitations The following geometric limitations for houses have been assumed: (a) The overall width at any section, excluding eaves and lean-to verandahs but including verandahs under the main roof, does not exceed 16.0 m. (b) The roof pitch does not exceed 35. (c) Roof shapes may be skillion or gable, hip or gable ended or any combination of these. (d) The number of trafficable floors supported by timber framing does not exceed two. (e) Wall height, measured from floor to ceiling, does not exceed 3.0 m. NOTE: For further definitions of these limitations refer to AS , AS and AS Design methods The design methods used are based upon analytical and engineering principles and comply with the requirements of AS System-based assumptions The design criteria include many system-based assumptions, which recognize the interactions between structural elements and other elements of the overall construction system. These assumptions are based upon the methods of assembly and materials given in AS , AS and AS NOTE: Changes in materials (both structural and non-structural) and the use of installation methods other than those given in AS , AS and AS , may invalidate the system-based assumptions contained in this Standard Durability The structural design criteria have been developed on the assumption that materials used and their installation and maintenance ensure that components will fulfil their intended structural function for the intended life of the structure. NOTE: In the selection of materials, specific consideration should be given to the risk of and resistance to biological attack and corrosion, long-term durability of adhesives and the long-term strength and rigidity of materials taking into account the short-term and long-term conditions of exposure. Standards Australia

10 AS Structural timber Member design for Span Tables in AS , AS and AS , is based upon the use of generic stress grades of scantling timber. NOTE: For other materials, the design procedures and assumptions may require modification in accordance with the requirements of AS Design properties The design properties given in AS for stress grades and strength groups have been used for design, except for F-grades the characteristic beam shear strengths given in Appendix A have been used Effect of temperature on strength The modification factor for the effect of temperature on strength (k 6 ) has been taken as unity regardless of location Design loads Dead loads Dead loads are based upon standardized allowances for the mass of roof, wall and floor constructions. NOTE: Where mass allowances different from those referred in the Standard are used, then such variation should be noted in any published data Live loads Generally, the live loads used for design correspond to those given in AS The following departures and interpretations have been used: (a) The partial-area live load for floor areas less than 10 m 2 is not considered. (b) The permanent component of floor live load is taken as 0.5 kpa. (c) To allow for balconies or decks 1 m or more above the ground, the cantilevered portion of floor joists and bearers and the main spans of floor joists and bearers for decks are designed for 3.0 kpa floor live load for the strength limit states and 1.5 kpa for the serviceability limit state. (d) The area used to calculate the distributed roof live load resultant from stacked materials or equipment used in repair or maintenance is taken as the area supported in the plane of the roof and not the plan projected area. (e) The occasional loading on roof and ceiling members is taken as 1.1 kn. NOTE: Live loads specific to construction, for example, loads resulting from the use of fall protection devices or scaffolding attached to the structure, are not considered Wind loads The free stream dynamic pressures for the strength limit state and the serviceability limit state are derived using AS for design wind speeds corresponding to wind classifications N1 to N4 and C1 to C3 as specified in Appendix B Snow loads Snow loads, determined in accordance with AS , up to 0.2 kpa have been considered and determined as not critical. For this reason, snow loading is not included in the load combinations given for member design in this Standard. Standards Australia

11 7 AS Earthquake loads Earthquake loads for earthquake load categories H1 and H2, that is for domestic structures, have been determined in accordance with AS and found not critical for design. For this reason, earthquake loads are not included in the load combinations given for member design or for the methods of determination of racking loads in AS and AS Load combinations Load combinations included for the determination of the strength limit states and the serviceability limit states for each member are those determined appropriate in accordance with AS Strength limit states For each member, all strength limit states have been considered; however, only those strength limit states deemed as potentially critical are included in the design criteria. NOTE: For other timber-based products, design may require consideration of strength limit states other than those included in this Standard Serviceability limit states The serviceability limit states used for the design have been determined on the basis of experience with the known serviceability performance of individual member types in typical applications. Serviceability limits used are intended to provide satisfactory rigidity for average situations. NOTES: 1 For installations where greater than usual rigidity may be required, then it is anticipated that larger sizes and or materials with higher or more uniform modulus of elasticity will be used (see AS ). 2 The limits on deflection used as part of the definition of the serviceability limit states are limits intended for comparison with calculated deflections only. Actual or measured deflections may differ from calculated deflections due to any or all of the following factors: (a) Differences between actual loads and design loads used for serviceability calculations. (b) Differences between the actual modulus of elasticity of components and the average value used for design. (c) Differences between the structural behaviour of the system and the structural models used for design. 1.5 DEFINITIONS For the purpose of this Standard, the following definitions apply Balcony An external trafficable floor area of a house including a deck that is 1 m or more above ground level Birdsmouth A triangular notch cut into the underside of a sloping beam (e.g. rafter) to permit seating on the supporting member Bracing An assembly intended to resist racking forces including diagonal members, shear panels, diaphragms, cantilevered columns or portal (rigid) frames Cladding Material used for the external surface of walls or roofs. Standards Australia

12 AS Flooring or decking Boards or sheets overlying floor joists intended to support floor loads. Flooring is usually tongue and groove jointed along the edges whereas decking is not Generic stress grades Stress grades for which properties are included in AS Lining The materials used for the internal faces of walls or ceilings Loadbearing walls Walls required to support vertical loads from roofs and/or floors. NOTE: This definition differs from that given in the Building Code of Australia Nogging A horizontal member fitted between studs in a wall frame which restrains the studs against buckling in the plane of the wall. Noggings may also be used for attachment of cladding or lining or as part of a bracing system Non-loadbearing walls Partition walls not supporting roofs or floors. Non-loadbearing walls may support ceilings. NOTE: This definition differs from that given in the Building Code of Australia Sheet roofing Includes sheet metal tile panels and other metal deck roofing of mass up to 10 kg/m Span The face to face distance between supports of a structural member measured along the axis of the member. NOTES: 1 This definition differs from that given in AS Truss spans have traditionally been measured from outside to outside of pitching plates Standard roof truss An engineered, triangulated framework installed at similar centres to rafters and designed to transfer roof and ceiling loads, usually, to external walls Tie-down The connections or fixings designed to resist uplift forces due to wind Tiled roofing Includes slate, terracotta and concrete tiles of mass up to 60 kg/m Wall/brick tie A bracket connecting brick cladding to a timber wall frame. 1.6 NOTATION Generally, the notation used in AS and the AS 1170 series is used also in this Standard. Notation specific to each clause is defined in that clause. Some general notation symbols used in this Standard are as follows: b = breadth of member CLW = ceiling load width Standards Australia

13 9 AS d = depth of member FLW = floor load width K c = pressure combination factor (see Section 6) L = general symbol used for span L o P = horizontal span for rafter overhang = general symbol for concentrated load RLW = roof load width S = general symbol used for spacing w = general symbol for distributed load Standards Australia

14 AS SECTION 2 DESIGN OF ROOF MEMBERS 2.1 ROOF BATTENS Description A roof batten is a rectangular section used on its flat to provide direct support for sheet or tile roofing. Spans for roof battens are limited to 1200 mm. For tile roofs a standard spacing of 330 mm is considered whereas for sheet roofs, spacings up to 1200 mm are included. Battens are assumed to span continuously over rafters (or trusses) for at least two spans (see Figure 2.1). Rafter or truss Roof batten Batten spacing Batten span Batten overhang FIGURE 2.1 ROOF BATTENS Design for Safety General consideration Design for safety includes consideration of the strength limit states for bending about the minor axis only and shear. NOTE: Battens are assumed to be prevented from bending in the plane of the roof by the attached cladding Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads (G) Dead loads, corresponding to the typical roof constructions, are determined as in Table TABLE DEAD LOAD FOR ROOF BATTENS Roof type Sheet roof Tile roof Dead load, G (kn/m) 0.1S + self weight 0.6S + self weight NOTE: S = spacing of roof battens, in metres. Standards Australia

15 11 AS (b) (c) Live loads The uniformly distributed live load, Q 1 (in kn/m), and concentrated live loads, Q 2 and Q 3 (both in kn), used for design are obtained as follows: (i) Q 1 = g 44 (0.9/L S) (1) (ii) Q 2 = g (2) (iii) Q 3 = g (3) where g 44 = the lesser of 1.33S and 1.0 L = span of roof battens, in metres S = spacing of roof battens, in metres and g 45 is calculated in accordance with Paragraph B3, Appendix B, assuming a bargeboard of rigidity E f I f = Nmm 2 is attached to the ends of the parallel overhanging battens, and g 47 = 1.0 (i.e. no birdsmouth notch). NOTES: 1 The formula for distributed live load is derived from the formula for roof live load given in AS , where the plan area is taken as 2LS and is always less than 14 m 2 for the spans and spacings considered. 2 The load distribution factor g 44 is taken from CSIRO, Low-rise domestic and similar framed structures (see Clause 1.2). The use of this load distribution factor is based upon construction workers following the traditional practice of not treading at or near midspan of closely spaced battens prior to the installation of roof claddings. Wind load The wind load, W u (in kn/m), applicable for the strength limit state, is calculated as follows: W u = q u C pt S (4) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S = spacing of roof battens, in metres TABLE NET PRESSURE COEFFICIENTS FOR ROOF BATTENS Wind classification N1 to N4 C1 to C3 C pt General areas Areas within 1.2 m of an edge +0.7, NOTES: 1 Local pressure effects are catered for in AS , AS and AS by notes attached to Span Tables specifying reductions in batten spacing near edges, as appropriate. 2 Values given in this Table are based on the assumption that a separate ceiling is provided and a maximum internal pressure coefficient (C pi ) in the roof cavity of +0.2 for both cyclonic and non-cyclonic regions. Standards Australia

16 AS Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load category 1 Structural model 1.25G G + 1.5Q 1 1.5Q G G 1.5Q G + W u G + W u Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category are given in Table TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Standards Australia

17 13 AS (b) Moisture content of timber: (i) Unseasoned timber for load category 3 given in Table 2.1.3, values of k 4 appropriate for thickness as specified in AS are used. For load categories 1 and 2, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Member restraint For battens, breadth is greater than or equal to depth and, hence, the lateral stability factor k 12 = Design for serviceability Loads The loads used for the serviceability limit states are given as follows: (a) Dead load (G) Dead loads corresponding to various typical roof constructions are determined as in Table (b) Wind load The uniformly distributed wind load, W s (in kn/m), applicable for the serviceability limit state is calculated as follows: W s = q s C pt S where q s = free stream dynamic gust pressure, in kpa, for the serviceability limit state; values of q s are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S = spacing of roof battens, in metres Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases included in Table are divided into load categories for the purpose of allowing for the effect of duration of load on stiffness as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Structural models G G 1 2 W s W s Standards Australia

18 AS Calculation of deflection The requirements of AS for the calculation of deformation are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Load duration factor (j 2 ) Moisture content Load category 1 (permanent loads) Load category 2 (transient loads) Seasoned Unseasoned Serviceability limits The limits on deflection defining the serviceability limit state are given in Table TABLE LIMITS ON DEFLECTION Load category Midspan Deflection limits End of overhang 1 Span/300 Overhang/150* or 4 mm whichever is greater 2 Span/150 No limitation * Ignore limit for upwards deflection Standards Australia

19 15 AS RAFTERS Description Rafters are roof members which run parallel to the fall of the roof and support roof battens or purlins. They may also support ceilings, either directly or via ceiling battens or joists. Rafters may be either single span or continuous span and may be cantilevered to form an eaves overhang either with or without a birdsmouth notch at the overhang support. Continuous span rafters are assumed not notched at intermediate supports. For the determination of the maximum overhang the ends of rafters are assumed rigidly connected to a fascia which acts to share any concentrated or partial area loads to adjacent members (see Figure 2.2). Rafter spacing Rafter spacing Ridgeboard Ridgeboard Underpurlin Ceiling joist Single span rafter Fascia Continuous span rafter Overhang span Fascia (a) Single span (b) Continuous span FIGURE 2.2 RAFTERS Design for safety General consideration Design for safety includes consideration of the strength limit states for bending and shear. In addition, for birdsmouth notches associated with overhangs, the interaction of bending and shear is also considered Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads (G) Dead loads, corresponding to various typical roof constructions, are determined as in Table Roof type Sheet roof only Sheet roof and ceiling Tile roof only Tile roof and ceiling TABLE DEAD LOAD Dead load, G (kn/m) 0.1S + self weight 0.2S + self weight 0.4S + self weight 0.6S + self weight 0.9S + self weight NOTE: S = spacing of rafters, in metres. Standards Australia

20 AS (b) Live loads The distributed live loads, Q 1, Q 2 and Q 3 (in kn/m), and concentrated live loads Q 4 and Q 5 (in kn), are determined as follows: (i) Q 1 = g S L (ii) Q 2 = g S L or 0.25S, whichever is greater (1) or 0.25S, whichever is greater (2) (c) (iii) Q 3 = g S or 0.25S, whichever is greater Lo (3) (iv) Q 4 = g (4) (v) Q 5 = g (5) where, L = span of rafters, in metres S = spacing of rafters, in metres L o = horizontal span of rafter overhang, in metres g 45 = load distribution factor for parallel rafter overhangs, calculated as detailed in Appendix C for the case where the depth of the birdsmouth notch is one third of the rafter depth and a fascia of minimum rigidity Nmm 2 is attached to the end of each rafter g 42, g 43 = are the load distribution factors for concentrated load and partial area load, respectively, applied to a grid system, calculated in accordance with AS , assuming the crossing members are battens with rigidity and spacing as follows: (1) Sheet roofs: E c I c = Nmm 2, and spacing = 1200 mm. (2) Tile roofs: E c I c = Nmm 2, and spacing = 330 mm. Wind loads The wind load, W u (in kn/m), applicable for the strength limit state is calculated as follows: W u = q u C pt S (6) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S = spacing of rafters, in metres TABLE NET PRESSURE COEFFICIENTS FOR RAFTERS STRENGTH Wind classification Main spans Standards Australia C pt Overhang N1 to N or or 1.6 C1 to C or or 1.6 NOTE: The positive net pressure coefficients include the pressure combination factor K c = 0.8, which allows for the combined effect of positive wind pressure on the roof and negative internal pressure.

21 17 AS Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load Structural model category Single span Continuous span Overhang G 1.25G 1.25G 1.25G + 1.5Q G + 1.5Q G 1.25G + 1.5Q Q G 1.5Q G 1.25G 1.5Q G + W u 1.25G + W u 1.25G + W u 3 0.8G + W u 0.8G + W u 0.8G + W u 0.8G + W u Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. In addition, for birdsmouth notches associated with rafter overhangs, the procedures given in Appendix C are applied, assuming the notch depth is one third of the rafter depth. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 2.2.3, are given in Table TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Standards Australia

22 AS (b) Moisture content of timber: (c) (d) (i) Unseasoned timber for load category 3 given in Table 2.2.3, values of k 4 appropriate for thickness as specified in AS are used. For load categories 1 and 2, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. Strength sharing For scantling timber, the strength sharing factor (k 9 ) has been determined as follows: (i) For the determination of the maximum main spans, k 9 has been determined in accordance with AS , assuming n mem = 5 and n com = 1 (for single members). (ii) For the determination of maximum overhangs and for negative moment only, in accordance with Appendix C k 9 = (S/L o ), but not less than (7) where S = spacing of rafters L o = horizontal span of the overhang Member restraint For the determination of bending capacity the following assumptions related to lateral restraint are used: (i) At supports rafters are assumed torsionally restrained at their supports. (ii) Between supports (A) the top edges of rafters are assumed laterally restrained by battens or purlins at 330 mm centres for tile roofs and 1200 mm centres for sheet roofs; and (B) in addition, continuous span rafters are assumed restrained against torsional buckling at the points of contraflexure taken as one quarter of the span from the intermediate support Design for serviceability Loads The loads used for the purpose of assessing the serviceability limit states are given as follows: (a) (b) Dead loads and live loads Dead loads and live loads are determined as described in Clause Wind loads The uniformly distributed wind load, W s (in kn/m), applicable for the serviceability limit state is calculated as follows: W s = q s C pt S where q s = free stream dynamic gust pressure, in kpa, for the serviceability limit state; values of q s are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S = spacing of rafters, in metres Standards Australia

23 19 AS TABLE NET PRESSURE COEFFICIENTS FOR RAFTERS SERVICEABILITY Wind classification Main spans C pt Overhangs N1 to N4 and C1 to C Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases included in Table are divided into load categories for the purpose of allowing for the effect of duration of load on stiffness, as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load Structural model category Single span Continuous span Overhang (cantilevered) G G G 1 Q 1 Q 2 2 Q 4 Q 4 Q W s W s W s W s Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table In addition, the deflection at the ends of overhangs for birdsmouth-notched rafters is determined using the modified rafter rigidity given in Appendix C Serviceability limits The limits on deflection, defining the serviceability limit state, are given in Table Standards Australia

24 AS TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor (j 2 ) Load category 1 Load category 2 or 3 Seasoned Unseasoned TABLE LIMITS ON DEFLECTION Load category Midspan Deflection limits End of overhang 1 Span/ mm 2 Span/ mm 3 Span/ mm Standards Australia

25 21 AS ROOF BEAMS RIDGE OR INTERMEDIATE BEAMS Description Ridge or intermediate beams are roof beams that support rafters, which in turn support roof or roof and ceiling loads. Roof beams run perpendicular to the slope of the roof, either single or continuous span and may cantilever to support a verge overhang. Overhang spans are determined assuming roof beams are not notched at the overhang support. For the purpose of determining lateral stability, roof beams are assumed to be laterally restrained by rafters fixed to their top edge (see Figure 2.3). Ridge beam Rafter Supports (post, wall, etc.) Ridge beam Intermediate beam Supports (post, wall, etc.) Ridge beam span Supporting wall or intermediate beam Intermediate beam span Supporting wall (a) Ridge beam (b) Intermediate beam FIGURE 2.3 ROOF BEAMS RIDGE OR INTERMEDIATE BEAM Design for safety General consideration Roof beam design for safety includes consideration of the strength limit state for bending, shear and bearing Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads The uniformly distributed dead load, G (in kn/m), corresponding to various typical roof constructions with additional allowance for the weight of the rafters, are determined as follows: G = 0.01(RM) (RLW) (RLW) 2 + self weight (1) where RM = standardized roof mass, i.e. 10, 20, 40, 60 or 90 kg/m 2 RLW = roof load width for the roof beam, in metres Standards Australia

26 AS (b) (c) Live loads The distributed live loads, Q 1 and Q 2 (in kn/m), and concentrated live load, Q 3 (in kn), are determined as follows: (i) 1.8 Q1 = ( RLW ) or 0.25(RLW), whichever is greater (2) L (ii) 0.9 Q2 = ( RLW ) or 0.25(RLW), whichever is greater (3) L (iii) Q 3 = (4) where L = span of roof beam, in metres RLW = roof load width for the roof beam, in metres Wind loads The uniformly distributed wind load, W u (in kn/m), applicable for the strength limit state is calculated as follows: W u = q u C pt (RLW) (5) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table RLW = roof load width for roof beam, in metres TABLE NET PRESSURE COEFFICIENTS FOR ROOF BEAMS STRENGTH Wind classification Main spans C pt Overhang N1 to N or or 1.6 C1 to C or or 1.6 NOTE: The positive net pressure coefficients include the pressure combination factor K c = 0.8, which allows for the combined effect of positive wind pressure on the roof and negative internal pressure Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending, shear and bearing. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 2.3.2, are given in Table Standards Australia

27 23 AS (b) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table 2.3.2, values of k 4 appropriate for thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load Structural model category Single span Continuous span Overhang G 1.25G 1.25G 1.25G + 1.5Q G + 1.5Q Q G 1.5Q G 1.25G 1.5Q G + W u 1.25G + W u 1.25G + W u G + W u 0.8G + W u 0.8G + W u 0.8G + W u TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) (c) (d) Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1 and n com = number of combined sections. Member restraint For the determination of bending capacity, the following assumptions relating to lateral restraint are used: (i) At supports roof beams are assumed torsionally restrained at their supports. (ii) Between supports: (A) The top edges of roof beams are assumed restrained at 1200 mm centres. (B) Continuous span roof beams are assumed restrained against buckling at the points of contraflexure. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination. Standards Australia

28 AS Design for serviceability Loads The loads used for the serviceability limit state are given as follows: (a) Dead loads and live loads Dead loads and live loads are determined as described in Clause (b) Wind loads The uniformly distributed wind load, W s (in kn/m), applicable for the serviceability limit state, is calculated as follows: W s = q s C pt (RLW) where q s = free stream dynamic gust pressure, in kpa, for the serviceability limit state; values of q s are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table RLW = roof load width for roof beam, in metres TABLE NET PRESSURE COEFFICIENTS FOR RAFTERS SERVICEABILITY Wind classification Main spans C pt Overhangs N1 to N4 and C1 to C Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases included in Table are divided into load categories for the purpose of allowing for the effect of duration of load on stiffness, as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load Structural model category Single span Continuous span Overhang (cantilevered) G G G 1 Q 1 Q 2 2 Q 3 Q 3 Q W s W s W s W s Standards Australia

29 25 AS Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor ( j 2 ) Load category 1 Load category 2 or 3 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Midspan Deflection limits End of overhang 1 Span/ mm 2 Span/ mm 3 Span/ mm Standards Australia

30 AS UNDERPURLINS Description Underpurlins provide intermediate support for rafters in coupled roof construction. They are orientated as shown in Figure 2.4 and primarily support roof loads normal to the plane of the roof over the middle part of the rafter length. Sections with depth to overall breadth ratios greater than four are not considered for application as underpurlins. Further, where the depth to overall breadth ratio exceeds two, underpurlins are assumed torsionally braced at supports and fly-braced back to rafters at intervals not exceeding 1200 mm along their span. These requirements are intended to minimize weak axis sag which may reduce support to rafters and/or induce buckling, particularly for more steeply pitched roofs. Ridgeboard Underpurlin span Rafter Underpurlin Roof strut Rafter spacing FIGURE 2.4 UNDERPURLINS Design for safety General consideration Design for safety includes consideration of the strength limit states in bending and shear Loads The loads used for determination of the design actions effects are determined as follows: (a) Dead loads Dead loads include the self weight of the underpurlin (G 1 ) and concentrated loads (G 2 ) imposed by the rafters. G 2 (in kn) is determined as follows: G 2 = 1.25 (0.01RM) S R (RLW) (1) where RM = standardized roof mass, i.e. 10, 20 or 60 kg/m 2 S R = spacing of rafters, i.e. 0.6 m or 1.2 m RLW = roof load width for underpurlin, in metres NOTE: The 1.25 factor in Equation 2.4.2(1) provides an allowance for the weight of supported rafters and the effect of their continuity. Standards Australia

31 27 AS (b) Live loads Live loads imposed via rafters are considered as concentrated loads, Q 1 (in kn), and are determined as follows: (c) 1.8 Q1 = SR ( RLW ) or 0.25 S R (RLW), whichever is greater (2) N where N = number of rafters supported over one span for the single span case, or over two spans for the continuous span case S R = spacing or rafters, i.e. 0.6 m or 1.2 m RLW = roof load width for underpurlins, in metres Wind loads Wind loads are considered as concentrated loads (W u ), imposed via the rafters. Concentrated loads, W u (in kn), are calculated as follows: W u = q u C pt S R (RLW) (3) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S R = spacing of rafters, i.e. 0.6 m or 1.2 m RLW = roof load width for underpurlin, in metres TABLE NET PRESSURE COEFFICIENTS FOR UNDERPURLINS Wind classification N1 to N4 or C1 to C3 C pt +0.7 or Structural models and load categories used for strength design The structural models used to determine the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category defined in Table are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3, values of k 4 appropriate for member thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1 and n com = number of combined sections. Standards Australia

32 AS (d) Member restraint For the determination of bending capacity, the following assumptions related to lateral restraint are used: (i) At supports underpurlins are considered torsionally restrained at their supports. (ii) Between supports: (A) The top edges of underpurlins are assumed restrained by rafters at 600 mm or 1200 mm centres, as appropriate. (B) Underpurlins with a depth to overall breadth ratio greater than two are assumed torsionally restrained at 1200 mm centres. (C) Continuous span underpurlins are assumed restrained against buckling at the points of contraflexure. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination and not the overall breadth. TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Design action Structural models effect Single span Continuous span P P P S R S R w P P P P S R S R S R S R P w In bending L P P P P S R S R S R w w P P P P P P S R S R S R S R S R In shear 1.5d 1.5d Load category Design loads 1 w = 1.25G 1 and P = 1.25G 2 2 w = 1.25G 1 and P = (1.25G Q 1 ) 3 w = 1.25G 1 and P = (1.25G 2 + W u ) w = 0.80G 1 and P = (0.8G 2 + W u ) NOTES: 1 S R is rafter spacing, either 0.6 m or 1.2 m. 2 The number of concentrated loads considered will vary according to span, rafter spacing and locations of concentrated loads. 3 Loads within 1.5d of supports are ignored in the determination of the design action effect in shear. Standards Australia

33 29 AS TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Design for serviceability Loads The loads used for the serviceability limit states are given as follows: (a) Dead loads Dead loads are determined as described in Clause (b) Live Loads Concentrated live loads, Q 1 (in kn), are determined as follows: 1.8 Q1 = SR ( RLW ) or 0.25 S R (RLW), whichever is greater N where N = number of rafters supported over one span for both the single and continuous span cases S R = spacing of rafters, i.e. 0.6 m or 1.2 m RLW = roof load width for underpurlin, in metres Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load Structural models category Single span Continuous span G 2 G 2 G 2 S R S R G 1 G 2 G 2 G 2 G 2 G 2 S R S R S R S R G 1 1 L 2 Q 1 Q 1 Q 1 S R S R Q 1 S R Q 1 Q 1 S R L NOTE: S R = rafter spacing Standards Australia

34 AS Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor ( j 2 ) Load category 1 Load category 2 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/300 2 Span/250 Standards Australia

35 31 AS STRUTTING BEAMS Description Strutting beams are near horizontal, single span beams installed within the roof space, clear of ceilings, which provide support to underpurlins via struts. Whilst strutting beams may be loaded by one or more struts located anywhere within the span, the design procedures given conservatively assume all roof load is applied via a single strut. Strutting beams are assumed torsionally braced at supports and at midspan (see Figure 2.5). Ridgeboard Underpurlin Roof strut Strutting beam span Strutting beam FIGURE 2.5 STRUTTING BEAMS Design for safety General consideration Design for safety includes consideration of the strength limit states for bending and shear Loads Roof loads applied to strutting beams are calculated on the basis of roof area supported. Design loads are calculated as follows: (a) Dead loads Dead loads for strutting beams include the self weight of the strutting beam, G 1 (in kn/m), and the roof dead load as a concentrated load, G 2 (in kn), calculated as follows: G 2 = 0.01 (RM + 10) A (1) where RM = standardized roof mass allowance, i.e. 20 kg/m 2 for sheet roofs and 60 kg/m 2 for tile roofs A = area of roof supported by the strutting beam, in square metres (b) Live loads Roof live load is considered applied as a concentrated load, Q 1 (in kn), calculated as follows: Q 1 = ( A) or 0.25A, whichever is greater (2) where A = area of roof supported by strutting beam in square metres Standards Australia

36 AS (c) Wind loads Wind load applicable for the strength limit state is considered applied as a concentrated load W u (in kn), calculated as follows: W u = q u C pt A (3) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table A = area of roof supported by the strutting beam, in square metres TABLE NET PRESSURE COEFFICIENTS FOR STRUTTING BEAMS Wind classification N1 to N4 C1 to C3 C pt +0.7 or Structural models and load categories for strength design The structural models used to calculate the member design action effect are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modification factors are used: (a) (b) (c) (d) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 2.5.2, are given in Table Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table 2.5.2, values of k 4 appropriate for thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1.0 and n com = number of combined sections. Member restraint For the determination of bending capacity the following assumptions relating to lateral restraint are used: (i) At supports strutting beams are assumed torsionally restrained at their supports. (ii) Between supports strutting beams having a depth to breadth ratio greater than three are assumed torsionally restrained at midspan (the assumed load point). NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination. Standards Australia

37 33 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Design action effect Structural models P w In bending P w In shear Load category L/3 2L/3 Design loads 1 w = 1.25G 1 and P = 1.25G 2 2 w = 1.25G 1 and P = 1.25G Q 1 3 w = 1.25G 1 and P = 1.25G 2 + W u w = 0.8 G 1 and P = 0.8G 2 + W u TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Design for serviceability Loads The dead loads and live loads used for the serviceability limit states are determined as specified in Clause Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Structural models G 2 G1 1 Q Standards Australia

38 AS Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor ( j 2 ) Load category 1 Load category 2 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/300 or 20 mm max. 2 Span/250 or 20 mm max. Standards Australia

39 35 AS COUNTER STRUTTING BEAMS Description Counter strutting beams support roof loads from struts and ceiling loads from hanging beams. For design, loading from both roof and ceiling is considered concentrated at midspan. Counter strutting beams are assumed torsionally braced at their supports and at midspan by the attachment of the hanging beams (see Figure 2.6). Ridgeboard Underpurlin Rafter Roof strut Counter strutting beam Hanging beam Counter strutting beam FIGURE 2.6 COUNTER STRUTTING BEAM Design for safety General consideration Design for safety includes consideration of the strength limit states in bending and shear Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads Dead loads include the self weight of the counter strutting beam (G 1 ) and the concentrated load due to the roof and ceiling loads, G 2 (in kn), which is calculated as follows: G 2 = 0.01(RM + 10) A + (0.06L L 2 ) (CLW) (1) where RM = standardized roof mass allowance, i.e. 20 kg/m 2 for sheet roofs and 60 kg/m 2 for tile roofs A = area of roof supported by the counter strutting beam, in square metres L = span of the counter strutting beam, in metres CLW = ceiling load width for the counter strutting beam, in metres Standards Australia

40 AS (b) (c) Live loads Roof live load is considered as a concentrated load, Q 1 (in kn), applied via a roof strut and calculated as follows: Q 1 = ( A) or 0.25A, whichever is greater (2) where A = roof area supported by the counter strutting beam, in square metres Wind loads Wind load is considered applied as a concentrated load, W u (in kn), applied via a single roof strut and calculated as follows: W u = q u C pt A (3) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table A = roof area supported by the counter strutting beam, in square metres TABLE NET PRESSURE COEFFICIENTS FOR COUNTER STRUTTING BEAM Wind classification C pt N1 to N or 1.1 C1 to C or 1.6 NOTE: The positive net pressure coefficients include the pressure combination factor K c = 0.8, which allows for the combined effect of positive wind pressure on the roof and negative internal pressure Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 2.6.1, are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table 2.6.2, values of k 4 appropriate for thickness as specified in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1.0 and n com = number of combined sections. Standards Australia

41 37 AS (d) Member restraint For the determination of bending capacity the following assumptions relating to lateral restraint are used: (i) (ii) At supports counter strutting beams are assumed torsionally restrained at their supports. Between supports counter strutting beams are assumed torsionally restrained at midspan. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination. TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Design action effect Structural models P w In bending P w In shear L/3 2L/3 Load category Design loads 1 w = 1.25G 1 and P = 1.25G 2 2 w = 1.25G 1 and P = 1.25G Q 1 3 w = 1.25G 1 w = 0.80G 1 and P = 1.25G 2 + W u and P = 0.8G 2 + W u TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor k Design for serviceability Loads The dead loads and live loads used for the serviceability limit states are determined as specified in Clause Standards Australia

42 AS Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Structural models G 2 G 1 1 Q Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor ( j 2 ) Load category 1 Load category 2 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/300 or 12 mm max. 2 Span/300 or 12 mm max. Standards Australia

43 39 AS COMBINED HANGING STRUTTING BEAMS Description Combined hanging strutting beams support roof loads applied via struts to the top edge and ceiling loads from ceiling joists along the bottom edge. For design, roof loads are conservatively assumed applied via a single strut and ceiling loads are assumed uniformly distributed (see Figure 2.7). Rafter Underpurlin Roof strut Ceiling joist Hanging- strutting beam Hanging-strutting beamspan FIGURE 2.7 COMBINED HANGING-STRUTTING BEAM Design for safety General consideration Design for safety includes consideration of the strength limit states for bending and shear Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads Dead loads include the distributed load due to self weight and the weight of the ceiling (G 1 ) and the concentrated load due to the weight of the roof (G 2 ). G 1 (in kn/m) and G 2 (in kn) are calculated as follows: (i) G 1 = 0.12(CLW) (CLW) 2 + self weight (1) (ii) G 2 = 0.01(RM + 10) A (2) where CLW = ceiling load width for combined hanging strutting beam, in metres RM = standardized roof mass allowance, i.e. 20 kg/m 2 for sheet roofs and 60 kg/m 2 for tile roofs Standards Australia

44 AS (b) (c) Live loads Roof live load is considered as a concentrated load, Q 1 (in kn), applied via a single roof strut and calculated as follows: Q 1 = ( A) or 0.25A, whichever is greater (3) where A = roof area supported by the combined hanging strutting beam, in square metres Wind loads Wind load is considered as a concentrated load, W u (in kn) applied via a single roof strut and calculated as follows: W u = q u C pt A (4) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table A = roof area supported by the combined hanging strutting beam in square metres TABLE NET PRESSURE COEFFICIENTS FOR COMBINED HANGING STRUTTING BEAM Wind classification C pt N1 to N or 1.1 C1 to C or 1.6 NOTE: The positive net pressure coefficients include the pressure combination factor K c = 0.8, which allows for the combined effect of positive wind pressure on the roof and negative internal pressure Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modification are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table 2.7.2, values of k 4 appropriate for thickness as specified in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1.0 and n com = number of combined sections. Standards Australia

45 41 AS (d) Member restraint For the determination of bending capacity, the following assumptions relating to lateral restraint are used: (i) At supports combined hanging strutting beams are assumed torsionally restrained at their supports. (ii) Between supports combined hanging strutting beams are assumed laterally restrained by ceiling joists at maximum 600 mm centres along their bottom edge. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination. TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Design action effect Structural models P w In bending P w In shear L/3 2L/3 Load category Design loads 1 w = 1.25G 1 and P = 1.25G 2 2 w = 1.25G 1 and P = 1.25G Q 1 3 w = 1.25G 1 w = 0.80G 1 and P = 1.25G 2 + W u and P = 0.8G 2 + W u TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Standards Australia

46 AS Design for serviceability Loads The dead loads and live loads used for the serviceability limit states are determined as specified in Clause Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Structural models G 2 G 1 1 Q Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor ( j 2 ) Load category 1 Load category 2 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/300 or 12 mm max. 2 Span/300 or 12 mm max. Standards Australia

47 43 AS CEILING BATTENS Description Ceiling battens are closely spaced continuously spanning members attached to the underside of rafters, ceiling joists, floor joists or trusses that provide direct support for ceiling linings. The design of ceiling battens does not include consideration of live load effects (see Figure 2.8.1). Ceiling joist Ceiling batten FIGURE CEILING BATTENS Design for safety General consideration Design for safety includes consideration of the strength limit state for bending Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads Dead load includes dead load due to self weight and due to the mass of the supported ceiling lining, G (in kn/m), which is calculated as follows: G = 0.12 S + self weight (1) where S = the spacing of the ceiling battens, in metres (b) Live loads Strength limit states for live load are not considered. (c) Wind loads Wind load for the strength limit state is considered applied as a uniformly distributed load, W u (in kn/m), and calculated as follows: W u = q u C pt S (2) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S = spacing of ceiling battens, in metres Standards Australia

48 AS TABLE NET PRESSURE COEFFICIENTS FOR CEILING BATTENS Wind classification C pt N1 to N or 0.5 C1 to C or Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load category Structural models 1.25G G + W u 2 0.8G + W u Member design capacity The requirements of AS are applied to determine member design capacities. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 2.8.2, are given in Table TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Standards Australia

49 45 AS (b) Moisture content of timber: (i) Unseasoned timber for load category 1, as defined in Table 2.8.2, k 4 = 1.0. For load category 2, values of k 4 appropriate for thickness as specified in AS are used. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing For ceiling battens, k 9 = 1.0. (d) Member restraint For ceiling battens breadth is greater than or equal to depth and, therefore, k 12 = Design for serviceability Loads Only the serviceability limit state for dead load is considered in design. Dead load for the serviceability limit state is determined as given in Clause Structural model for serviceability design The structural model for which deflection is calculated is shown in Figure G FIGURE STRUCTURAL MODEL FOR SERVICEABILITY DESIGN Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor ( j 2 ) Seasoned 2.0 Unseasoned Serviceability limit The serviceability limit state is defined by limiting the calculated deflection to span/ Standards Australia

50 AS CEILING JOISTS Description Ceiling joists are closely spaced members primarily intended to support ceiling linings attached to their bottom edge. Ceiling joists also act to tie rafters together in coupled roof construction. However, for design, the axial load is ignored (see Figure 2.9). Dead and wind loads are assumed continuously applied along the bottom edge of the joists. Live load due to construction or maintenance is considered applied as a concentrated load to the top edge. Two installation methods are considered. One in which a continuous over-batten is attached to the top edge of each joist at midspan and acts to laterally distribute the concentrated live load and provide intermediate lateral restraint. For the alternative method, no over-batten is installed and design does not allow for any load distribution or intermediate lateral restraint. Ceiling joist Hanging beam Rafter Overbatten Ceiling joist spacing Ceiling joist span FIGURE 2.9 CEILING JOISTS Design for safety General consideration Design for safety includes consideration of the strength limit states for bending and shear Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead load Dead load, G (in kn/m) for ceiling joists supporting ceiling lining (and battens, if appropriate), as follows: G = 0.12S + self weight (1) where S = spacing of ceiling joists, in metres Standards Australia

51 47 AS (b) (c) Live loads Live load for ceiling joists is considered as a concentrated load, Q (in kn), and calculated as follows: Q = g (2) Where g 42 is a load distribution factor calculated as follows: (i) For ceiling joists installed without over-batten, g 42 = 1.0. (ii) For ceiling joists installed with a midspan over-batten: (A) Bending g 42 is determined in accordance with AS for concentrated loads on grid systems, assuming the rigidity of the crossing member (over-batten), E c I c is equal to Nmm 2 and the number of crossing members is one. (B) Shear g 42 = 1.0. Wind loads The wind load, W u (in kn/m), applicable for the strength limit state is calculated as follows: W u = q u C pt S (3) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S = spacing of ceiling joists, in metres TABLE NET PRESSURE COEFFICIENTS FOR CEILING JOISTS STRENGTH Wind classification C pt N1 to N or 0.5 C1 to C or Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration k 1. Values of k 1 appropriate for each load category, as defined in Table 2.9.3, are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table 2.9.3, values of k 4 appropriate for thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing Strength sharing is ignored, k 9 = Standards Australia

52 AS (d) Member restraint For the determination of bending capacity the following assumptions relating to lateral restraint are used: (i) At supports ceiling joists are assumed torsionally restrained at supports. (ii) Between supports: (A) For dead load and the dead load plus downward wind load cases the bottom edge is assumed loaded and continuously restrained. (B) For net upward wind load plus dead load, the bottom edge is assumed continuously restrained. (C) For the dead load plus live load case, the top edge is assumed loaded and not restrained (i.e. L ay = span), except for ceiling joists installed with over-battens, L ay is taken as one half the span. TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load Structural models category Single span Continuous span G 1.25G 1.5Q 1.25G 1.5Q 1.25G G + W u 1.25G + W u 3 0.8G + W u 0.8G + W u TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Standards Australia

53 49 AS Design for serviceability Loads Only the serviceability limit for dead load is considered. Dead loads for calculation of deflection are given in Clause Structural model for serviceability design The structural models for which deflection is calculated are shown in Table TABLE STRUCTURAL MODEL SERVICEABILITY Single span Continuous span G G Calculation of deflection The requirements of AS are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load duration factor ( j 2 ) Seasoned 2.0 Unseasoned Serviceability limits The serviceability limit state is defined by limiting the calculated deflection to span/400 or 12 mm maximum. Standards Australia

54 AS HANGING BEAMS Description Hanging beams are used to provide support for ceiling joists where supporting walls are widely spaced. They are installed in the roof cavity above the ceiling joists, which are attached to the bottom edge. Design assumes that hanging beams are single span beams, loaded and continuously restrained by ceiling joists along their bottom edge (see Figure 2.10). Hanging beam Ceiling joist Hanging beam span FIGURE 2.10 HANGING BEAM Design for safety General consideration Design for safety includes consideration of the strength limit state for bending Loads The loads used to calculate the design action effects are determined as follows: (a) Dead load The uniformly distributed dead load, G (in kn/m), is calculated as follows: G = 0.12 (CLW) (CLW) 2 + self weight (1) where CLW = ceiling load width for the hanging beam, in metres (b) Live load A concentrated live load, Q = 1.1 kn is considered. (c) Wind load The uniformly distributed wind load applicable for the strength limit state, W u (in kn/m), is calculated as follows: W u = q u C pt (CLW) (2) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table CLW = ceiling load width for the hanging beam, in metres Standards Australia

55 51 AS TABLE NET PRESSURE COEFFICIENTS FOR HANGING BEAMS STRENGTH Wind classification C pt N1 to N or 0.5 C1 to C or Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load category Structural models 1.25G 1 1.5Q 1.25G G + W u 3 0.8G + W u Member design capacity The requirements of AS are applied to determine member design capacities in bending. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table , are given in Table Standards Australia

56 AS (b) (c) (d) TABLE LOAD DURACTION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table , values of k 4 appropriate for thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0. Strength sharing Where multiple sections of scantling timber are nail-laminated the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1.0 and n com = number of combined sections. Member restraint The following assumptions relating to lateral restraint are used: (i) At supports hanging beams are assumed torsionally restrained at supports. (ii) Between supports hanging beams are considered loaded and continuously restrained along their bottom edge. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination Design for serviceability Loads The dead and live loads used for the serviceability limit states are determined as specified in Clause Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause TABLE STRUCTURAL MODEL SERVICEABILITY Load category Structural models G 1 Q 2 Standards Australia

57 53 AS Calculation of deflection The requirements of AS are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Initial moisture content Load duration factor ( j 2 ) Load category 1 Load category 2 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/300 2 Span/270 Standards Australia

58 AS COUNTER BEAMS Description A counter beam is a ceiling member running parallel to ceiling joists and usually between them which provides support for hanging beams. The hanging beams are assumed butted to the sides of the counter beam (see Figure 2.11). Hanging beam Counter beam span Ceiling joist Counter beam FIGURE 2.11 COUNTER BEAM Design for safety General consideration Design for safety includes consideration of the strength limit states for bending Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads Dead loads include the distributed load due to self weight G 1 (in kn/m), and a concentrated load imposed by the hanging beams, G 2 (in kn), which is calculated as follows: G 2 = 0.2 (CLW) (L/2) (1) where CLW = ceiling load width for the counter beam, in metres L = span of the counter beam, in metres (b) Live load A concentrated live load, Q = 1.1 kn, is considered. Standards Australia

59 55 AS (c) Wind load Wind load is considered as a concentrated load, W u (in kn), and is calculated as follows: W u = q u C pt (CLW) (L/2) (2) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table CLW = ceiling load width for the counter beam, in metres L = span of the counter beam in metres TABLE NET PRESSURE COEFFICIENTS FOR COUNTER BEAMS Wind classification C pt N1 to N or 0.5 C1 to C or Structural models and load categories for strength design The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load category Structural models 1.25G G G G Q G G 2 + W u 3 0.8G 1 0.8G 2 + W u Standards Australia

60 AS Member design capacity The requirements of AS are applied to determine member design capacities. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table are given in Table (b) (c) (d) TABLE LOAD DURACTION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3, given in Table , values of k 4 appropriate for thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1.0 and n com = number of combined sections. Member restraint For the determination of bending capacity the following assumptions relating to lateral restraint are used. (i) (ii) At supports counter beams are assumed torsionally restrained at their supports. Between supports counter beams are assumed torsionally restrained at midspan by the supported hanging beams. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination Design for serviceability Loads The dead loads and live loads used for the serviceability limit states are determined as specified in Clause Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause Standards Australia

61 57 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Structural models G 2 G 1 1 Q Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Initial moisture content Load duration factor ( j 2 ) Load category 1 Load category 2 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/300 or 15 mm max. 2 Span/270 or 15 mm max. Standards Australia

62 AS VERANDAH BEAMS Description Verandah beams span between verandah posts and support roof loads imposed by rafters or trusses. Verandah beams for single and continuous span applications are considered. Design considers roof load is applied to the top edge of verandah beams as a series of concentrated loads at 600 mm or 1200 mm centres corresponding to rafter (or truss) spacings (see Figure 2.12). Verandah beam Rafter or truss Rafter or truss spacing Verandah beam span FIGURE 2.12 VERANDAH BEAM Design for safety General consideration Design for safety includes consideration of the strength limit states in bending and shear Loads The loads used for determination of the design action effects are determined as follows: (a) Dead loads Dead loads include the self weight of the verandah beam, G 1 (in kn/m), and concentrated loads (G 2 ) imposed by the rafters. G 2 (in kn) is determined as follows: G 2 = 0.01 (RM) (RLW) S R (RLW) 2 S R (1) where RLW = roof load width for the verandah beam, in metres RM = standardized roof mass, i.e. 10, 20, 40, 60 or 90 kg/m 2 S R = rafter spacing, i.e. 0.6 m or 1.2 m Standards Australia

63 59 AS (b) Live loads Live loads imposed via rafters are considered as concentrated loads, Q (in kn), and calculated as follows: (c) where N N R or 0.25 S R (RLW), whichever is greater (2) Q = 0.12 S ( RLW ) S R = number of rafters supported over one span for the single span case, or over two spans for the continuous span case = rafter spacing, i.e. 0.6 m or 1.2 m RLW = roof load width for the verandah beams, in metres Wind loads Wind loads are considered as concentrated loads W u (in kn), imposed via the rafters and calculated as follows: W u = q u C pt S R (RLW) (3) where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients given in Table S R = rafter spacing, i.e. 0.6 or 1.2 m RLW = roof load width for the verandah beam, in metres NOTE: Horizontal wind pressure on verandah beams is ignored. TABLE NET PRESSURE COEFFICIENTS FOR VERANDAH BEAMS Wind classification N1 to N4 or C1 to C3 C pt +0.4 or Structural models and load categories used for strength design The structural models used to determine the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category defined in Table are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3, values of k 4 appropriate for member thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. Standards Australia

64 AS (c) (d) Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1 and n com = number of combined sections. Member restraint For the determination of bending capacity, the following assumptions related to lateral restraint are used: (i) (ii) At supports verandah beams are considered torsionally restrained at their supports. Between supports: (A) The top edges of verandah beams are assumed restrained by rafters at 600 mm or 1200 mm centres as appropriate. (B) Continuous span verandah beams are assumed restrained against buckling at the points of contraflexure taken as one quarter of the span from an intermediate support. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination and not the overall breadth. TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Design action Structural models effect Single span Continuous span P P P S R S R w P P P P S R S R S R S R P w In bending L P P P P S R S R S R w w P P P P P P S R S R S R S R S R In shear 1.5d 1.5d Load category Design loads 1 w = 1.25G 1 and P = 1.25G 2 2 w = 1.25G 1 and P = (1.25G Q) 3 w = 1.25G 1 and P = (1.25G 2 + W u ) w = 0.8 G 1 and P = (0.8G 2 + W u ) NOTES: 1 S R is rafter spacing, either 0.6 m or 1.2 m. 2 The number of concentrated loads considered will vary according to span, rafter spacing and locations of concentrated loads. 3 Loads within 1.5d of supports are ignored in the determination of the design action effect in shear. Standards Australia

65 61 AS TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Design for serviceability Loads The loads used for the serviceability limit states are given as follows: (a) Dead loads Dead loads are determined as described in Clause (b) Live loads Concentrated live loads, Q (in kn), are determined as follows: (c) where N N R or 0.25 S R (RLW), whichever is greater (1) Q = S ( RLW ) S R = number of rafters supported over one span for both the single and continuous span cases = rafter spacing, i.e.0.6 m or 1.2 m RLW = roof load width for the verandah beam, in metres Wind loads Wind load is considered applied by the rafters as a series of concentrated loads, W s (in kn), and calculated as follows: W s = q s C pt S R (RLW) (2) where q s = free stream dynamic gust pressure, in kpa, for the serviceability limit state; values of q s are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients give in Table S R = rafter spacing, i.e. 0.6 m or 1.2 m RLW = roof load width for verandah beam, in metres TABLE NET PRESSURE COEFFICIENTS FOR VERANDAH BEAMS Wind classification N1 to N4 C1 to C3 C pt +0.4, Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause Standards Australia

66 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load Structural models category Single span Continuous span G 2 G 2 G 2 S R S R G 1 G 2 G 2 G 2 S R S R S R G 2 G 2 S R G 1 1 L 2 Q Q Q S R S R Q Q Q S R S R L W s W s W s S R S R W s W s W s S R S R S R W s S R W s 3 L NOTE: S R = rafter spacing 0.6 m or 1.2 m Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Initial moisture content Load duration factor ( j 2 ) Load category 1 Load categories 2 and 3 Seasoned Unseasoned Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/400 or 10 mm max. 2 Span/250 or 12 mm max. 3 Span/200 Standards Australia

67 63 AS SECTION 3 DESIGN OF WALL MEMBERS 3.1 POSTS Description Posts are vertical loadbearing columns designed to support axial loads arising from the vertical support given to roofs and floors. Posts may be incorporated within or installed separate from walls. Posts are not used to replace common studs in external walls and are, therefore, not designed to support lateral loads. Posts are assumed laterally supported only at points of attachment to floor and roof members (see Figure 3.1). Post Post FIGURE 3.1 POSTS SUPPORTING ROOF AND/OR FLOOR LOADS Design for safety General consideration Design for safety includes consideration of the strength limit states in tension and compression Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads Dead load is determined as the sum of the dead loads from supported roof and floor areas. Expressions used for the determination of concentrated dead load (G) are given in Table Standards Australia

68 AS TABLE DEAD LOADS Source of load Floor Roof: Tile Sheet Dead load, G (kn) 0.4 A F 0.9 A R 0.4 A R NOTE: A F = area of floor supported in square metres A R = area of roof supported in square metres (b) (c) Live loads Concentrated live loads, Q 1, Q 2 and Q 3 (all in kn), arising from support given to floor and roof areas are determined as follows: (i) For posts supporting floor area (A F ): (A) Permanent live load Q 1 = 0.5 A F. (B) Transient live load Q 2 = 1.5 A F. (ii) For posts supporting roof area (A R ) Q 3 = ( A R ) or 0.25 A R, whichever is greater. NOTES: 1 Live loads Q 2 and Q 3 are not considered to act simultaneously. 2 Units for areas A F and A R are square metres. Wind loads The concentrated wind load, W u (in kn), applicable for the strength limit state arising from support given to roof areas is calculated as follows: W u = q u C pt A R where q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients for roof areas supported by posts, as given in Table = roof area supported, in square metres A R TABLE NET PRESSURE COEFFICIENTS FOR ROOF AREAS SUPPORTED BY POSTS STRENGTH Wind classification N1 to N4 or C1 to C3 C pt or Structural models and load categories for strength design Posts are designed as simple columns supporting an axial concentrically applied load. Load * combinations used to determine the design action effects in compression ( N c ) and tension * ( N t ) are given in Table Design action effects given in Table are divided into load categories that are used for the determination of the corresponding member design capacity as specified in Clause Standards Australia

69 65 AS TABLE DESIGN ACTION EFFECTS AND LOAD CATEGORIES STRENGTH Load categories Design action effects 1 N * c = 1.25 (G + Q 1 ) 2 N * c = 1.25 G Q 2 3 N * c = 1.25 (G + Q 1 ) Q 3 4 N * c = 1.25 (G +Q 1 ) + W u N * t = 0.8 G + W u Member design capacity The requirements of AS are applied to determine member design capacities in compression and tension. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 3.1.3, are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load categories 2, 3 and 4, values of k 4 appropriate for thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing Strength sharing is not considered to apply for posts, i.e. k 9 = 1.0. (d) Member restraint For the determination of the compressive capacity of posts the effective length for buckling about either axis is taken as 0.85 times the post height. Post height is the distance between supports and points of attachment to supported floor and roof members, which are assumed to provide lateral restraint for both axes of buckling. NOTE: Nail-laminated posts are not considered in this Standard. TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Design for serviceability Axial deformation of posts under the applicable loadings is small and for this reason serviceability design for posts is disregarded. Standards Australia

70 AS LOADBEARING WALL STUDS Description Loadbearing wall studs are the vertical components of a loadbearing wall required to transfer tension or compression loads from supported floors or roofs and to transfer horizontal wall loads, in bending, to the top and bottom wall supports. Common studs support the vertical loads applied to the top wall plate by rafters, ceiling joists or floor joists and the horizontal loads due to wind. Jamb studs are studs each side of opening, which support loads from the lintel over the opening and horizontal wind loads related to the width of the opening. Studs supporting concentrated loads are studs installed in the wall in addition to common studs (or jamb studs) required to carry concentrations of vertical load arising from support for principal roof or floor supporting members. Special consideration is given for studs notched for the installation of bracing. For notched studs, notches are assumed in either face of the wall penetrating to a maximum depth of 20 mm in the depth of the studs (see Figure 3.2). Rafter/truss spacing Rafter of truss Rafter or truss spacing Upper floor joist Stud height Stud height Stud spacing (a) Single or upper storey Stud (b) Lower storey Stud spacing FIGURE 3.2 LOADBEARING WALL STUDS Standards Australia

71 67 AS Design for safety General consideration Design for safety includes consideration of the strength limit states in compression, tension, bending, combined bending and compression and combined bending and tension. For notched studs the strength limit state for combined bending and shear at the assumed notch location is also determined Loads The loads used for the determination of the design action effects are determined as follows: (a) Dead loads The concentrated dead loads (G) considered axially applied to common studs, jamb studs and studs supporting concentrated loads in upper or single storey walls or lower storey of two-storey walls are determined as given in Table TABLE AXIAL DEAD LOADS SUPPORTED BY STUDS Application Common studs Jamb studs Studs supporting concentrated loads Axial dead loads, G (kn) Upper storey or single storey walls (a) sheet roof 0.4 (RLW)S (RLW) (W o / ) 0.4 A R (b) tile roof 0.9 (RLW)S (RLW) (W o /2+ 0.3) 0.9 A R Lower storey walls of twostorey construction (a) Roof, upper wall and floor: sheet roof tile roof [0.4 (RLW) (FLW) (FLW) 2 ] S 2 [0.4(RLW) (FLW) (FLW) 2 ] (W o / ) [0.9 (RLW) (FLW) (FLW) 2 ] S 2 [0.9 (RLW) (FLW) (FLW) 2 ] (W o / ) (b) Floor only [0.4 (FLW) (FLW) 2 ] S 2 [0.4 (FLW) (FLW) 2 ] (W o / ) 0.4 A F LEGEND: S 1 = the greater of the rafter (truss) or stud spacing in the wall, in metres S 2 = the greater of the floor joist or stud spacing in the lower wall, in metres W o = width of opening in the wall, in metres A R = area of roof supported by the stud, in square metres A F = area of floor supported by the stud, in square metres RLW = roof load width supported by the wall, in metres FLW = floor load width supported by the wall, in metres Standards Australia

72 AS (b) Live loads Concentrated live loads, Q 1, Q 2 and Q 3 considered axially applied to common studs, jamb studs and studs supporting concentrated loads in upper or single storey walls or the lower storey of two-storey construction are determined as given in Table TABLE AXIAL LIVE LOADS SUPPORTED BY STUDS Application Upper storey or single storey walls Lower storey walls of two-storey Common studs Jamb studs Axial live loads (kn) Q 1 = 0 Q 1 = 0 Q 1 = 0 Studs supporting concentrated loads Q 2 = 0.25 (RLW)S 1 Q 2 = 0.25 (RLW)(W o /2 +0.3) Q 2 = 0.25 A R Q 3 = 0 Q 3 = 0 Q 3 = 0 Q 1 = 0.5 (FLW)S 2 Q 1 = 0.5 (FLW) (W o / ) Q 1 = 0.5 A F Q 2 = 0 Q 2 = 0 Q 2 = 0 construction Q 3 = 1.5 (FLW)S 2 Q 3 = 1.5 (FLW) (W o / ) Q 3 = 1.5 A F LEGEND: RLW = roof load width supported by the wall, in metres FLW = floor load width supported by the wall, in metres S 1 = greater of the rafter/truss or stud spacing, in metres S 2 = greater of the floor joist or stud spacing, in metres W o = width of opening in the wall, in metres A R = area of roof supported by the stud, in square metres A F = area of floor supported by the stud, in square metres Q 1 = long-term component of floor live load Q 2 = roof live load Q 3 = short term floor live load Standards Australia

73 69 AS (c) Wind loads Wind loads for studs are considered applied as axial concentrated loads (W ua ) and uniformly distributed lateral loads (W uw ). Expressions used for the determination of W ua and W uw for common studs, jamb studs and studs supporting concentrated loads are determined as given in Table TABLE AXIAL AND LATERAL WIND LOADS FOR STUDS Type of load Common studs Jamb studs Studs supporting concentrated loads Studs in upper W ua (kn) q u C ptr (RLW) S 1 q u C ptr (RLW) (W o / ) q u C ptr A R storey or single storey walls W uw (kn/m) q u C ptw S s q u C ptw (W o / ) Not applicable Studs in lower W ua (kn) q u C ptr (RLW) S s q u C ptr (RLW) (W o / ) Not considered storey walls of twostorey construction W uw (kn/m) q u C ptw S s q u C ptw (W o / ) Not applicable LEGEND q u = free stream dynamic gust pressure for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C ptr = net pressure coefficients for roof areas supported by the wall as given in Table C ptw = net pressure coefficients for walls, as given in Table S 1 = greater of the rafter or stud spacing, in metres S s = stud spacing, in metres W o = width of opening between jamb studs, in metres A R = roof area supported, in square metres TABLE PRESSURE COEFFICIENTS FOR ROOF AND WALLS STRENGTH Wind classification C ptr C ptw N1 to N or C1 to C or NOTE: Positive pressure coefficient indicates an inwards pressure Structural models and load categories for strength design The structural model used to calculate the member design action effects is shown in Table For the determination of design action effects, axial loads are assumed concentrically applied and maximum bending moments are determined as given in Table Load combinations given in Table are divided into load categories that are used for the determination of the corresponding member design capacity as specified in Clause Standards Australia

74 AS TABLE STRUCTURAL MODEL AND LOAD CATEGORIES STRENGTH Structural model Common stud Jamb stud Studs supporting concentrated loads P = axial, concentric load P P Uniformly distributed lateral load (w) L w L L NOTES: 1 For notched studs, the notch is assumed located at mid-height. 2 M = cwl 2 where (a) for L 2.4 m, c = 0.07; (b) for L 4.2 m, c = 0.125; and (c) for 2.4 < L < 4.2, c = ( L 0.003). M = w L 2 M = 0 Load category Design loads 1 P = 1.25 (G + Q 1 ) and w = 0 2 P = 1.25 G + 1.5Q 3 and w = 0 3 P = 1.25 G + 1.5Q 2 and w = 0 4 P = 1.25 (G + Q 1 ) + K c W ua and w = K c W uw P = 0.8G + K c W ua and w = K c W uw P = 1.25 (G + Q 1 ) and w = W uw NOTE: Where K c = 0.8 is the wind pressure combination factor applicable where load effect results from wind pressure on two or more surfaces Member design capacity The requirements of AS are applied to determine member design capacities in compression, tension and bending and in combined bending and compression and bending and tension. The following assumptions and modifications factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 3.2.5, are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load category 4 give in Table 3.2.5, values of k 4 appropriate for thickness as specified in AS are used. For load categories 1, 2 and 3, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. Standards Australia

75 71 AS (c) (d) (e) Strength sharing: (i) For common studs the strength sharing factor (k 9 ) is applied for bending only, assuming n mem = 5 and n com = number of sections combined in a stud. (ii) For jamb studs the strength sharing factor (k 9 ) is applied for bending only, with n mem = 1.0 and n com = number of sections combined in the jamb stud. (iii) For studs supporting concentrated loads the strength sharing factor (k 9 ) is not applied. Member restraint For the determination of bending and compressive capacity, the following assumptions relating to lateral restraint are used: (i) For bending: (A) At supports Studs are assumed torsionally restrained. (B) Between supports studs are assumed torsionally and laterally restrained by noggings; L ay = 1350 mm. In addition, the tension edge is assumed laterally restrained at intervals not greater than 600 mm. (ii) For compression (A) For buckling about the major axis the effective length of studs is taken as g 13 L, where L is the height of the stud and g 13 is determined as follows: (1) For common studs: L 2.4 m, g 13 = 0.75 L 4.2 m, g 13 = m L 4.2 m, g 13 = (0.139 L ) (2) For jamb studs g 13 = 0.9. (B) For buckling about the minor axis, L ay is taken as 600 mm. NOTE: For studs formed by nail laminating one or more sections together, the breadth of section used to determine the slenderness coefficients (S 1 or S 4 ) is taken as the breadth of an individual lamination. Notched studs for studs up to 125 mm deep and notched to a maximum depth of 20 mm for the installation of diagonal bracing only, the bending capacity is determined as 0.6 times the bending capacity of an un-notched stud. The tensile and compressive capacities are determined using the net cross-section at the notch as the effective cross-sectional area. NOTE: The method used for studs notched for diagonal bracing is based upon CSIRO BCE Report, Notched composite beams, Dec. 97/169M, September TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Standards Australia

76 AS Design for serviceability General consideration Only the serviceability limit state for lateral deformation is considered. NOTE: The application of a serviceability limit state for serviceability wind pressure on the walls is assumed to ensure adequate lateral rigidity for incidental horizontal live loads Loads The distributed wind loads (W sw ) used for the serviceability limit state for common studs and for jamb studs are determined as shown in Table TABLE HORIZONTAL WIND LOAD SERVICEABILITY Common stud Type of stud W sw (kn/m) q s C ptw S Jamb stud q s C ptw (W o / ) LEGEND: q s = free stream dynamic gust pressure for the serviceability limit state; values of q s are given in Table B2, Appendix B, for each wind classification C ptw = net pressure coefficient for walls given in Table S = spacing of studs, in metres W o = width of opening in wall, in metres TABLE NET PRESSURE COEFFICIENTS FOR WALLS SERVICEABILITY Wind classification Net pressure coefficient for walls (C ptw ) N1 to N4 or C1 to C Structural model for serviceability design The structural model used to determine deflection under a uniformly distributed lateral load is given in Table For studs notched for the installation of bracing the presence of notches is ignored in the determination of deflection. Standards Australia

77 73 AS TABLE STRUCTURAL MODEL FOR DETERMINATION OF DEFLECTION For common studs Structural model For jamb studs Lateral load, w L Lateral load, w L NOTE: Max. deflection is calculated as follows: Deflection = c w L 4 /(EI) where (a) for L 2.4 m, c = ; (b) for L 4.2 m, c = 0.013; and (c) for 2.4 < L < 4.2, c = (0.0049L ) w = W sw. NOTE: Max. deflection is calculated as follows: Deflection = c w L 4 /(EI) where c = w = W sw Calculation of deflection Deflection of studs under the serviceability wind load specified in Clause is calculated assuming the structural model specified in Clause No modification is required for duration of load for this case Serviceability limit The deflection of common studs and jamb studs under the serviceability wind load given in Clause and calculated in accordance with Clause , is limited to (stud height)/150, but not greater than 20 mm. NOTE: This limit may not preclude damage to brittle surface finishes. Standards Australia

78 AS WALL PLATES FOR LOADBEARING WALLS Description Wall plates are the usually horizontal components in a wall frame to which the studs are attached at the top of the wall frame (top plate) and at the bottom of the wall frame (bottom plate). Where load or support points for a wall frame are not closely aligned with studs, or tiedown supports, then the wall plates in a loadbearing frame are designed to transfer load or support from a rafter/truss or floor joist, as appropriate, to adjacent studs, or tie-down points for top plates in upper storey or single storey walls. Where concentrated loads from girder trusses or other principal roof or floor supporting members occur then special provision for support of such loads (e.g. studs supporting concentrated loads, bridging or blocking) is assumed. Wall plates are not designed to transfer horizontal loads laterally to braced cross walls; ceiling and floor diaphragms are assumed to perform this function (see Figure 3.3). Rafter or truss spacing Rafter or truss Top plate (single or upper storey) Upper floor joist Upper floor joist spacing Bottom plate (single or upper storey) Stud Top plate (lower storey of two storeys) Stud Stud spacing Bottom plate (lower storey of two storeys) Stud spacing (a) Single or upper storey (b) Lower storey of two storeys FIGURE 3.3 WALL PLATES FOR LOADBEARING WALLS Standards Australia

79 75 AS Design for safety General consideration Wall plate design for safety includes consideration of the strength limit states for minor axis bending and shear Loads The vertical dead loads, live loads and wind loads used for the determination of the design action effects for top and bottom plates in upper storey or single storey walls and for lower storey walls of a two-storey construction are determined as follows: (a) Dead loads the concentrated dead load (G) is determined as given in Table Application TABLE DEAD LOADS FOR WALL PLATES Dead load, G (kn) Upper storey or single storey Top plates G = 0.01 RM (RLW) S R walls Bottom plates G = 0.01 RM (RLW) S S S S Lower storey walls Top plates Bottom plates LEGEND: RM = roof mass allowance (a) 40 kg/m 2 for sheet roofs; and (b) 90 kg/m 2 for tile roofs RLW = roof load width supported by wall, in metres FLW = floor load width supported by wall, in metres S R = spacing of rafters/trusses, in metres S S = spacing of studs in wall, in metres S J = spacing of floor joists, in metres G =0.01 RM (RLW) S J S J (FLW) S J (FLW) 2 S J G =0.01 RM (RLW) S S S S (FLW) S S (FLW) 2 S S (b) Live loads the concentrated live loads (Q 1, Q 2 and Q 3 ) are given in Table TABLE LIVE LOADS FOR WALL PLATES Application Live loads (kn) Upper storey or Top plates Q 1 = 0 Q 2 = 0.25 (RLW) S R Q 3 = 0 single storey walls Bottom plates Q 1 = 0 Q 2 = 0.25 (RLW) S S Q 3 = 0 Lower storey of Top plates Q 1 = 0.5 (FLW) S J Q 2 = 0 Q 3 = 1.5 (FLW) S J two storeys Bottom plates Q 1 = 0.5 (FLW) S S Q 2 = 0 Q 3 = 1.5 (FLW) S S LEGEND: RLW = roof load width supported by the wall, in metres FLW = floor load width supported by the wall, in metres S R = spacing of rafters/trusses, in metres S S = spacing of studs in wall, in metres S J = spacing of joists, in metres Q 1 = long-term component if live load Q 2 = roof live load Q 3 = short-term floor live load Standards Australia

80 AS (c) Wind loads the concentrated wind load (W u ) considered acting vertically on wall plates is determined as given in Table TABLE VERTICAL WIND LOADS ON WALL PLATES Application Upper storey or single storey walls Lower storey of two storeys Top plates Bottom plates Top plates Bottom plates Wind load, W u (kn) q u C ptr (RWL) S T q u C ptr (RWL) S S q u C ptr (RWL) S J q u C ptr (RWL) S S LEGEND: q u = free stream dynamic gust pressure for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C ptr = net pressure coefficients for roof areas given in Table RLW = roof load width supported by the wall, in metres S T = tie-down spacing tos top plate, in metres S S = spacing of studs in wall, in metres S J = spacing of floor joists supported by wall, in metres TABLE PRESSURE COEFFICIENTS FOR ROOF Wind classification C ptr N1 to N or 1.1 A1 C1 to C or 1.5 NOTE: Positive indicates inwards (downwards) pressure Structural models and load categories used for strength design The design action effects for the strength limit states are determined assuming wall plates are three span beams loaded by equally spaced concentrated loads arranged as shown in Table The spacing between loads and the design spans assumed for each type of wall plate are given in Table The design loads and the load combination used for their computation are also given in Table The design loads shown in Table are divided into load categories that are used for the determination of the corresponding member design capacities as specified in Clause Standards Australia

81 77 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES FOR WALL PLATES STRENGTH For determination of design action effect in bending Structural model For determination of design action effect in shear P S R P P P S R S R P S R P S R P L/2 L/2 L L L 1.5d L L LEGEND: S R = load spacing (see Table 3.3.6) L = span (see Table 3.3.6) d = depth of plate P = concentrated load (see Table 3.3.7) NOTE: For design action effect in shear, loads within 1.5d of supports may be ignored. TABLE LOAD SPACING AND SPANS FOR WALL PLATES Application Load spacing (S) Span (L) Upper storey or Stud spacing except for uplift, tiedown spacing Top plate Rafter/truss spacing single storey walls Bottom plate Stud spacing in wall Joist spacing Lower storey of Top plate Upper floor joist spacing Stud spacing in lower storey wall two storeys Bottom plate Stud spacing in lower storey wall Ground storey floor joist spacing TABLE DESIGN LOADS FOR WALL PLATES STRENGTH Load category Design loads 1 P = 1.25 (G + Q 1 ) 2 P = 1.25 G Q 3 3 P = 1.25 (G + Q 1 ) Q 2 4 P = 1.25 (G + Q 1 ) + K c W u P = 0.8 G + W u NOTE: Where K c = 0.8 is the wind pressure combination factor, applicable where the load effect results from wind pressure on two or more surfaces. Standards Australia

82 AS Member design capacity The requirements of AS are applied to determine member design capacities in bending and shear. The following assumptions and modifications factors are used: (a) Load duration factor the member design capacity includes the modification factor for load duration (k 1 ). Values of k 1, appropriate for each load category defined in Table 3.3.7, are given in Table TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) (b) Moisture content of timber: (i) Unseasoned timber for load categories 2, 3 and 4, values of k 4 appropriate for member thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing where multiple plates are used (ribbon plates) the strength sharing factor (k 9 ) is applied for the combination, assuming n mem = 1.0 and n com = number of sections combined. (d) Member restraint wall plates are bent about their weak axis and, therefore, k 12 = 1. (e) Composite action for nail-laminated multiple plates (ribbon plates) composite action is ignored. (f) Trenches the effect on strength of trenches up to 3 mm depth is ignored Design for serviceability Loads The dead loads and live loads used for the serviceability limit states are determined as described in Clause Structural model and load categories for serviceability design Deflections are calculated assuming wall plates are three span continuous beams supporting uniformly spaced concentrated loads (P) with one load positioned at the middle of an end span. The design loads corresponding to the selected serviceability load combinations are given in Table Design loads given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause Standards Australia

83 79 AS TABLE DESIGN LOADS AND LOAD CATEGORIES SERVICEABILITY Load categories Design loads 1 P = G + Q 1 2 P = Q 2 P = Q Calculation of deflection The requirements of AS for the calculation of deflection are applied using the duration of load factor for creep deformation, j 2 given in Table for load categories defined in Table The effect on deflection of trenches up to 3 mm deep and any composite action of nail-laminated ribbon plates is ignored. TABLE LOAD DURATION FACTORS FOR DEFORMATION Initial moisture content Load category 1 Load category 2 Seasoned Unseasoned Serviceability limits The limits on deflection corresponding to the serviceability limit states defined in Clause are given in Table TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 or 2 Span/200 or 3 mm max. Standards Australia

84 AS LINTELS Description Lintels are beams contained within loadbearing walls over windows or doors. They transfer the vertical loads applied over the opening to the jamb studs on each side. For single or upper storey walls, common lintels are designed to support regularly spaced rafters or trusses. Design criteria are also included for lintels, which, in addition to rafters, support a concentrated load from a roof principal such as a strutting beam or girder truss. Lintels in lower storey walls of a two-storey construction are designed to support uniformly distributed loads from the wall above including the roof loads supported by the upper wall and loads from an upper storey floor. Lintels are designed as part of a system that includes consideration of the contribution of roof battens, wall plates, jack studs and lintel trimmers. For lintels, the limits on design deflections have been determined in order to maintain clearances between the frame and the window or door frames contained within the wall (see Figure 3.4). Rafter or truss spacing Rafter or truss Jack stud Lintel (single or upper storey) Stud Lintel span Lintel trimmer Lintel (lower storey of two storeys) Stud Lintel span (a) Single or upper storey (b) Lower storey of two storeys FIGURE 3.4 LINTELS Standards Australia

85 81 AS Design of safety General consideration Design for safety includes consideration of the strength limit states in bending, shear and bearing Loads For lintels in single or upper storey walls, loads from rafters are considered applied as regularly spaced uniform concentrated loads. Where load from a roof principal is supported, an additional load related to the area of roof supported by the roof principal is considered. For lintels in lower storey walls, roof, wall and floor loads are considered uniformly distributed. Dead loads, live loads, and wind loads are determined as follows: (a) Dead loads The dead loads considered include a uniformly distributed load (G 1 ) regularly spaced uniform concentrated loads (G 2 ) and, where a roof principal is supported, a single concentrated load (G 3 ). Values of G 1, G 2 and G 3 are determined as given in Table TABLE DEAD LOADS Application Dead loads Unit Lintels in single or upper G 1 = self weight kn/m storey walls common G 2 = 0.01 (RM) (RLW) S R kn lintels G 3 = 0 Lintels in upper or single storey walls supporting a concentrated roof load Lintels in lower storey of two-storey construction G 1 = self weight G 2 = 0.01 (RM)(RLW) S R G 3 = 0.01 (RM) A R G 1 = self weight (RM)(RLW) (FLW) (FLW) G 2 = G 3 = 0 LEGEND: RM = roof mass 40 kg/m 2 for sheet roofs 90 kg/m 2 for tile roofs RLW = roof load width supported by wall, in metres A R = area of roof in square metres, supported by the lintel via a roof principal FLW = floor load width supported by the wall, in metres S R = rafter spacing, 0.6 m or 1.2 m kn/m kn kn kn/m Standards Australia

86 AS (b) Live loads The concentrated live loads (Q 1 and Q 2 ) for lintels in single or upper storey walls, and the distributed live loads (Q 3, Q 4 and Q 5 ) for lintels in lower storey of two storeys are given in Table TABLE LIVE LOADS FOR LINTELS Application Live loads Unit Lintels in single or upper storey walls common lintels Lintels in single or upper storey walls supporting concentrated roof loads Lintels in lower storey of two-storey construction 1. 8 Q 1 = N Q 1 = MS R (RLW) Q 2 = MA R where, M = S R (RLW) or 0.25 S R (RLW), whichever is greater kn AR + N SR ( RLW ) Q 3 =0.25 (RLW) Q 4 = 0.50 (FLW) Q 5 =1.50 (FLW) or 0.25 kpa, whichever is greater LEGEND: A R = area of roof supported by the lintel via a roof principal N = number of equally spaced rafters supported by the lintel S R = spacing in metres of the equally spaced rafters, 0.6 m or 1.2 m RLW = roof load width supported by the wall, in metres FLW = floor load width for the upper floor supported by the lower storey wall, in metres Q 1, Q 2 and Q 3 = roof live loads Q 4 = permanent floor live load Q 5 = short term floor live load kn kn/m Standards Australia

87 83 AS (c) Wind loads The concentrated wind loads for lintels in single or upper storey walls (W U1 and W U2 ) are determined as given in Table TABLE WIND LOADS FOR LINTELS Application Wind loads Unit Lintels in single or upper storey walls common lintels W U1 = q u C pt S R (RLW) kn Lintels in single or upper storey walls supporting a concentrated roof load W U1 = q u C pt S R (RLW) W U2 = q u C pt A R Lintels in lower storey of two-storey construction (See Note below) LEGEND: q u = free stream dynamic gust pressure for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficient given in Table A R = area of roof supported by the lintel via a roof principal S R = spacing in metres of the equally spaced rafters, 0.6 m or 1.2 m RLW = roof load width supported by the wall, in metres NOTE: Wind load for lower storey is not considered. kn TABLE NET PRESSURE COEFFICIENTS FOR LINTELS Wind classification C ptr N1 to N or 1.1 C1 to C or 1.6 NOTE: The positive net pressure coefficients include the pressure combination factor, K c = 0.8, which allows for the combined effect of positive wind pressure on the roof in combination with negative internal pressure. Standards Australia

88 AS Structural models, design loads and load categories The structural models and design loads used to determine the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used in the determination of corresponding member design capacities as specified in Clause TABLE STRUCTURAL MODELS FOR LINTELS STRENGTH Structural model Design action effect Lintels in single or upper storey walls Common lintels Lintels supporting concentrated roof loads Lintels in lower storey walls of two storeys For bending P 1 P 1 P 1 S R S R w P 1 (P 1 +P 2 ) S R S R P 1 w w For shear and bearing P 1 P 1 P 1 S R S R 1.5d w (P 1 +P 2 ) P 1 P 1 S R S R 1.5d w w Load category 1 Design loads w = 1.25 G 1 w = 1.25 G 1 w = 1.25 (G 1 + Q 4 ) P 1 = 1.25 G 2 P 1 = 1.25 G 2 P 2 = 1.25 G 3 2 w = 1.25 (G 1 + Q 4 ) Q 5 3 w = 1.25 G 1 w = 1.25 G 1 P 1 = 1.25 G Q 1 P 1 = 1.25 G Q 1 w = 1.25 (G 1 + Q 4 ) Q 3 P 2 = 1.25 G Q 2 w = 1.25 G 1 w = 1.25 G 1 P 1 = 1.25 G 2 + W U1 P 1 = 1.25 G 2 + W U1 P 2 = 1.25 G 3 + W U2 4 w = 0.8 G 1 w = 0.8 G 1 P 1 = 0.8 G 2 + W U1 P 1 = 0.8 G 2 + W U1 P 2 = 0.8 G 3 + W U2 NOTE: S R is rafter spacing, either 0.6 m or 1.2 m. Standards Australia

89 85 AS Design action effects in bending and shear The design action effects applied to the lintel in bending and shear, M* (in knm) and V* (in kn) respectively, are determined as follows: M* = M 0.55 k (1) V* = V 7.0 k (2) where M = maximum bending moment, in knm, determined using the design loads and structural models given in Table V = maximum shear force, in kn, determined using the design loads and structural models given in Table k 1 = duration of load factor for strength given in Table for the corresponding load category given in Table NOTE: The above expressions include an allowance for the contribution made by parallel members, such as roof battens and wall plates, in the support of the loads assumed applied to the lintel. TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Member design capacity The requirements of AS are applied to determine member design capacities in bending, shear and bearing. The following assumptions and modification factors are used: (a) Load duration factor The member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category defined in Table are given in Table (b) Moisture content of timber: (i) For unseasoned timber For load categories 3 and 4, values of k 4 appropriate for member thickness as given in AS are used. For load categories 1 and 2, k 4 = 1.0. (ii) For seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing Where multiple sections of scantling timber are nail-laminated, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1 and n com = number of combined sections. (d) Member restraint For the determination of bending capacity, the following assumptions relating to lateral restraint are used: (i) At supports lintels are considered torsionally restrained at their supports. (ii) Between supports lintels are assumed torsionally restrained at 600 mm centres. NOTE: Where nail-laminated members are used, the breadth of member used to derive the slenderness coefficient (S 1 ) is taken as the breadth of an individual lamination and not the overall breadth. Standards Australia

90 AS Design for serviceability Loads The loads used for the serviceability limit states are given as follows. (a) Dead and live loads The concentrated and uniformly distributed dead and live loads applied to lintels are determined as given in Clause (b) Wind Loads For lintels in single or upper storey walls, wind load is considered applied as a series of regularly spaced uniform concentrated loads (W S1 ) and, where a roof principal is supported, an additional concentrated load (W S2 ). W S1 and W S2 (both in kn) are determined as follows. W S1 = q s C pt S R (RLW) (1) W S2 = q s C pt A R (2) where q s = free stream dynamic gust pressure, in kpa, for the serviceability limit state; values of q s are given in Table B2, Appendix B, for each wind classification C pt = net pressure coefficients give in Table S R = rafter spacing, 0.6 m or 1.2 m RLW = roof load width for lintel, in metres = area of roof supported by the lintel via the roof principal A R TABLE NET PRESSURE COEFFICIENTS FOR LINTELS Wind classification N1 to N4 C1 to C3 C pt +0.7, Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table Load cases given in Table are divided into load categories for the purpose of allowing for duration of load on stiffness as specified in Clause Calculation of deflection The deflection of lintels is calculated taking into account the contribution of parallel members by adding an allowance for their rigidity, EI = 21.3 x 10 9 Nmm 2, to the rigidity of the lintel. The requirements of AS 1720 for the calculation of deflection are applied using the duration of load factor for creep deformation as given in Table Serviceability limits The limits on deflection used to define the serviceability limit states are given in Table Standards Australia

91 87 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Structural model Lintels in single or upper storey walls Common lintels G 2 G 2 G 2 S R S R Lintels supporting concentrated roof loads (G G 2 +G 3 ) 2 G 1 S R S R G 2 Lintels in lower storey walls of two storeys G 1 G 1 +Q 4 1 Q 1 Q 1 Q 1 S R S R Q 1 (Q 1 +Q 2 ) S R S R Q 1 Q 3 2 Q 5 3 W S1 W S1 W S1 S R S R W S1 S R (W S1 +W S2 ) WS1 S R 4 NOTE: S R is rafter spacing, either 0.6 m or 1.2 m. TABLE LOAD DURATION FACTORS FOR DEFORMATION Initial moisture content Load duration factor ( j 2 ) Load category 1 Load categories 2, 3 and 4 Seasoned Unseasoned TABLE LIMITS ON DEFLECTION Load category Deflection limits 1 Span/300 or 10 mm max. 2 Span/250 or 15 mm max. 3 Span/360 or 10 mm max. 4 Span/200 Standards Australia

92 AS SECTION 4 DESIGN OF FLOOR MEMBERS 4.1 FLOOR JOISTS Description Floor joists are closely spaced parallel beams supporting overlying flooring. Their primary purpose is to support floor loads. Floor joists may also be required to support ceilings and loadbearing walls, which may run either parallel or perpendicular to the direction of the joists (see Figure 4.1). Floor bearer Floor joist Roof Loads Roof Loads Loadbearing wall Joist span Joist span Joist spacing FIGURE 4.1 FLOOR JOISTS Design for Safety General consideration Floor joist design for safety includes consideration of the strength limit state for bending, shear and bearing Loads The values of the dead loads and live loads used for design are determined as follows: (a) Dead loads Table gives expressions used for the determination of uniformly distributed dead loads (G 1 ) and concentrated dead loads (G 2 ). TABLE DEAD LOADS Source of load Distributed load, G 1 (kn/m) Floor only: floor mass up to 40 kg/m S + self weight floor mass up to 100 kg/m S + self weight Loadbearing walls supporting roof loads. Wall perpendicular to joists but offset from supports: tile roof sheet roof Concentrated load, G 2 (kn) 0 0 (RLW ) S (RLW ) S NOTES: 1 S = spacing of joists in metres and RLW = roof load width in metres. 2 For any particular case, combine the loads from each source to obtain the total. Standards Australia

93 89 AS (b) Live Loads Table gives equations for the determination of distributed live loads (Q 1 to Q 4 ) and concentrated live loads (Q 5 and Q 6 ). For the determination of the concentrated live load (Q 5 ), a load distribution factor (g 42 ) is considered to apply for the joist grid system as follows: (i) For bending the value of the load distribution factor g 42, for concentrated loads applied anywhere within the middle half of the floor joist span and at least two joists in from the edge is determined in accordance with the requirements of AS assuming the crossing member is flooring of the following nominal rigidity: (A) For joist spacing 450 mm, E c I c = L (Nmm 2 ) and n c = 1.0. (B) For joist spacing > 450 mm but 600 mm, E c I c = L (Nmm 2 ) and n c = 1.0. where E c I c = flexural rigidity of the flooring L = span of floor joists, in mm n c = number of crossing members (flooring) (ii) For shear and bearing g 42 = 1.0. TABLE LIVE LOADS Type of load Load Unit Permanent Q UDL 1 = 0.5 S kn/m Transient UDL (houses) Partial UDL UDL (balcony or decks) Conc. (houses) Balcony line load NOTE: S = spacing of joists in metres Q 2 = 1.5 S Q 3 = 0.75 S Q 4 = 3.0 S Q 5 = g Q 6 = 1.5 S kn/m kn/m kn/m kn kn Structural models and load categories for strength The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories used for the determination of member design capacity as specified in Clause Standards Australia

94 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load category Single span Continuous span Overhang (cantilevered) 1.25G 2 * 1.25(G 1 + Q 1 ) 1.25G 2 * 1.25(G 1 + Q 1 ) 1.25(G 1 + Q 1 ) G 2 * 1.25G Q G 2 * 1.25G Q G G Q 2 (1.25G Q 5 )* 1.25G 1 (1.25G Q 5 )* 1.25G G G Q 4 1.5Q G For deck joists only: For deck joists only: 1.25G Q G Q 4 * Concentrated loads, G 2 and Q 5, are considered applied at mid-span (as shown) for bending, or at 1.5d from supports for shear, or at supports for bearing. G 2 does not apply where joists do not support loadbearing walls perpendicular to the joists Member design capacity The requirements of AS are applied to determine member design capacities in bending, shear and bearing. The following assumptions and modification factors are used: (a) Load duration factor the member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category are given in Table Standards Australia

95 91 AS TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) (b) (c) (d) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table 4.1.3, values of k 4 appropriate to thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. Strength sharing for sawn timber floor joists, the strength sharing factor (k 9 ) is applied, assuming n mem = 5 and n com = 1.0. Member restraint for the determination of bending capacity the following assumptions regarding lateral restraint are used: (i) At supports floor joists are assumed rotationally and torsionally restrained at their supports. (ii) Between supports: (A) The top edges of joists are assumed continuously laterally restrained. (B) Continuous span joists are assumed restrained against buckling at the points of contraflexure. That is, for the negative moment case, L ay = L/ Design for serviceability General consideration Floor joist design for serviceability includes consideration of the serviceability limit states for flexural deformation and dynamic behaviour Loads Dead loads and live loads used for the serviceability limit state are given as follows: (a) Dead loads expressions for the determination of the uniformly distributed dead load G 1, and concentrated dead load G 2, are given in Table (b) Live loads equations for the determination of distributed live loads (Q 1 to Q 4 ) and concentrated live load (Q 6 ) are given in Table Concentrated load, Q 7 (in kn), is determined as follows: Q 7 = g Where g 41 is the load distribution factor given in AS for point loads applied at the mid-span of beams in a grid system. The factor g 41 is calculated using the same assumptions as used to calculate g 42 in Clause NOTE: The limit on deflection resultant from the application of the Q 7 load is intended to ensure satisfactory dynamic performance. The application of this criterion replaces the need to separately consider deflection due to the 1.8 kn concentrated live load for floors Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table The load cases given in Table are divided into load categories for the purpose of allowing for the effect of duration of load on stiffness, as specified in Clause Standards Australia

96 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Single span Continuous span Overhang (cantilevered) G 2 G 1 + Q 1 G 2 G 1 + Q 1 G 1 + Q 1 1 Q2 Q 3 Q 2 Q 2 2 Q Q 7 Q Calculation of deflection The requirements of AS for the calculation of deflections are applied using the load duration factor for flexural deformation ( j 2 ) as given for each load category in Table Serviceability limits For the purpose of assessing the serviceability limit states, the limits on deflection for each of the load categories detailed in Table are given in Table TABLE LOAD DURATION FACTORS FOR DEFORMATION Moisture content Load category 1 (permanent loads) Load duration factor ( j 2 ) Load categories 2 and 3 (transient loads) Seasoned Unseasoned TABLE LIMITS ON DEFLECTION Load category Single or continuous span Limits on deflection Overhang (cantilever) 1 Span/300 or 15 mm max. Overhang/150* or 6 mm max. 2 Span/360 or 9 mm max. Overhang/180* or 4.5 mm max. 3 2 mm * Where the deflection at the end of the cantilever is upwards, ignore the overhang/150 or overhang/180 limit. Standards Australia

97 93 AS BEARERS Description Bearers are beams providing direct support for floor joists but in addition may support loads from loadbearing walls supporting roof loads and/or from upper storey floors. Design includes consideration of single, continuous or cantilevered span applications. Concentrated dead loads resulting from support to posts or intersecting loadbearing walls at locations other than at or near bearer supports are not considered (see Figure 4.2). Upper floor joist Upper floor joist spacing Floor joist Bottom plate Top plate Loadbearing wall Loadbearing wall Floor bearer Bearer span Bottom plate Floor bearer Bearer span = pier, stump or other support (a) Single or upper storey (b) Lower storey of two storeys FIGURE 4.2 BEARER SUPPORTING LOADBEARING WALL Design for safety General consideration Design for safety includes consideration of the strength limit states for bending, shear and bearing. Standards Australia

98 AS Loads The loads used for determination of the design action effects are determined as follows: (a) Dead loads the uniformly distributed dead load (G) for each bearer type is obtained by summing the loads from each applicable load source. Loads used for each load source are given in Table TABLE DEAD LOADS Source of load Bearer supporting floor joists only. Distributed dead load, G (kn/m) 0.4 (FLW) (FLW) 2 + self weight Add the following, as applicable: (a) Support to parallel loadbearing walls single storey double storey (b) Support to roofs sheet roof tile roof 0.4 (RLW) 0.9 (RLW) (c) Support to floor above 0.4 (FLW) (FLW) 2 LEGEND: FLW = floor load width, in metres, for the relevant floor RLW = roof load width, in metres, for the roof supported by the bearer (b) Live loads distributed live loads Q 1, Q 2, Q 4 and Q 5 and concentrated live loads Q 3 and Q 6 are determined for each application, as appropriate, using the equations given in Table TABLE LIVE LOADS Live load and application Permanent due to floor directly supported (kn/m) due to floor above, if applicable (kn/m) Load Q 1 = 0.5 (FLW) (FLW) 2 Transient (a) Distributed load due to floor directly supported (kn/m) due to floor above, if applicable (kn/m) Q 2 = 1.5 (FLW) (FLW) 2 (b) Concentrated load (kn) Q 3 = 1.8 (c) Cantilevered bearers supporting balcony distributed balcony load (kn/m) distributed back-span load (kn/m) balcony line load (kn) Q 4 = 3.0 (FLW) 1 Q 5 = 0.75 (FLW) 1 Q 6 = 1.5 (FLW) 1 (d) Distributed load for decks Q 7 = 3.0 (FLW) 1 LEGEND: (FLW) 1 = floor load width, in metres, for the directly supported floor (FLW) 2 = floor load width, in metres, for a supported floor above NOTE: Roof live loads are not considered to be applied at the same time as full floor live load. Standards Australia

99 95 AS Structural models and load categories for strength The structural models used to calculate the member design action effects are given in Table Load combinations shown in Table are divided into load categories that are used for the determination of member design capacity as specified in Clause Member design capacity The requirements of AS are applied to determine member design capacities in bending, shear and bearing. The following assumptions and modification factors are used: (a) Load duration factor the member design capacity includes the modification factor for load duration (k 1 ). Values of k 1 appropriate for each load category, as defined in Table 8.10, are given in Table (b) Moisture content of timber: (i) Unseasoned timber for load categories 2 and 3 given in Table 4.2.3, values of k 4 appropriate to thickness as given in AS are used. For load category 1, k 4 = 1.0. (ii) Seasoned timber k 4 = 1.0 for all load categories. (c) Strength sharing for nail-laminated members, the strength sharing factor (k 9 ) is applied for the combined member, assuming n mem = 1.0 and n com = number of combined sections. (d) Member restraint for the determination of bending capacity the following assumptions relating to lateral restraint are used: (i) At supports bearers are assumed torsionally restrained at their supports. (ii) Between supports: (A) The top edges of bearers are assumed laterally restrained along the top edge by floor joists spaced at 600 mm centres. (B) Continuous span bearers are assumed restrained against buckling at the point of contraflexure. That is, for the negative moment case, L ay = L/4. Standards Australia

100 AS TABLE STRUCTURAL MODELS AND LOAD CATEGORIES STRENGTH Load category Single span Continuous span Cantilevered 1.25(G +Q 1 ) 1.25(G +Q 1 ) 1.25(G +Q 1 ) G +1.5Q G +1.5Q G 1.25G +1.5Q 2 1.5Q G 1.5Q G 1.25G 1.5Q G + 1.5Q G For deck bearers only: For deck bearers only: 1.25G +1.5Q G +1.5Q 7 NOTE: Concentrated load, Q 3 is considered applied at midspan (as shown) for bending, or at 1.5d from supports for shear, or at supports for bearing. TABLE LOAD DURATION FACTORS FOR STRENGTH Load category Load duration factor (k 1 ) Design for serviceability Loads The dead loads and live loads used to determine deflections for the serviceability limit state are determined as follows: (a) Dead loads the uniformly distributed dead load (G) is determined as specified in Clause Standards Australia

101 97 AS (b) Live Loads uniformly distributed live loads (Q 1, Q 2 and Q 3 ) and concentrated live loads (Q 4 and Q 5 ) are determined as specified in Table TABLE LIVE LOADS SERVICEABILITY Type of load Permanent: due to floor directly supported (kn/m) due to floor above, if applicable (kn/m) Q 1 = 0.5 (FLW) 1 Load (FLW) 2 Transient (see Note below) (a) Distributed load (kn/m) Q 2 = 1.5 (FLW) 1 (b) Concentrated load (kn) Q 4 = 1.8 Q 3 = 0.75 (FLW) 1 (c) Balcony line load (kn) Q 5 = 1.5 (FLW) 1 LEGEND: (FLW) 1 = floor load width, in metres, for the floor directly supported by the bearer (FLW) 2 = floor load width, in metres, for floor above, if applicable NOTE: Only the transient live load on the floor directly supported is considered Structural models and load categories for serviceability design The structural models for which deflections are calculated are given in Table The load cases given in Table are divided into load categories for the purpose of allowing for the effect of duration of load on stiffness, as specified in Clause Calculation of deflection The requirements of AS for the calculation of deflection are applied using the load duration factor for flexural deformation ( j 2 ) as given for each load category in Table TABLE STRUCTURAL MODELS AND LOAD CATEGORIES SERVICEABILITY Load category Single span Continuous span Cantilevered G + Q 1 G + Q 1 G + Q 1 1 Q 2 Q 3 Q 2 Q 2 2 Q 4 Q 4 Q Standards Australia

102 AS TABLE LOAD DURATION FACTORS FOR DEFORMATION Initial moisture content Load category 1 (permanent loads) Load duration factor ( j 2 ) Load category 2 (transient loads) Seasoned Unseasoned Serviceability limits For the purpose of assessing the serviceability limit states, the limits on deflection used for each of the load categories detailed in Table are given in Table Load category TABLE LIMITS ON DEFLECTION Single or continuous span Limits on deflection Overhang (cantilever) 1 Span/300 or 12 mm max. Overhang/150* or 6 mm max. 2 Span/360 or 9 mm max. Overhang/180* or 4.5 mm max. * Where the deflection at the end of the cantilever is upwards, ignore the overhang/150 or overhang/180 limits. Standards Australia

103 99 AS SECTION 5 DETERMINATION OF UPLIFT FORCES 5.1 SCOPE AND GENERAL Scope of Section This Section describes how the net uplift pressures and net uplift forces given in AS and AS for the determination of tie-down requirements have been determined General Net uplift forces are the difference between the ultimate uplift forces due to wind and the factored gravity loads due to dead load and any permanent component of live load resisting uplift. In AS and AS the uplift forces to be resisted for tie-down are determined as the product of the roof area supported and the net uplift pressures given for the level where the tie-down is located. For uplift pressures at bottom plate or subfloor level where overturning may contribute to uplift and, therefore, height and width of the structure are also relevant, the uplift pressures given in AS and AS are equivalent values derived assuming the uplift load width is one half the building width. The values tabulated in AS and AS are upper bound values applicable where the ratio of height (h) to width (w) does not exceed one (see Figure 5.1). 5.2 DETERMINATION OF NET UPLIFT PRESSURES Roof uplift Net uplift forces for tie-down connections between roof members or for the roof frame assembly to supporting walls or directly to floor frames or slab are given as follows: (a) Roof battens The net uplift pressures to be resisted by tie-down connectors at each rafter, p u * (kpa) is given by the following equation: p u *=q u C pt 0.8 G (1) where, C pt = net pressure coefficient for roof battens given in Table 5.1 G = dead load of roof, 0.1 kpa for sheet roofs or 0.6 kpa for tile roofs. TABLE 5.1 NET PRESSURE COEFFICIENTS FOR ROOF BATTENS UPLIFT Wind classification General areas C pt Areas within 1.2 m of an edge N1 to N C1 to C Standards Australia

104 AS (b) Roof frame to wall or directly to floor frame or slab The net uplift pressure at each tie-down, p u * (kpa), is given by the following equation: p u *=q u C pt 0.8 G (2) where C pt = net pressure coefficient for roof uplift as given in Table 5.2. G = dead load of roof taken as 0.4 kpa for sheet roofs, or 0.9 kpa for tile roofs A1 TABLE 5.2 NET PRESSSURE COEFFICIENTS FOR ROOF UPLIFT Wind classification Tile roof Sheet roof C pt N1 and N N3 and N C1 to C Net uplift pressures at bottom plate or subfloor level The net uplift pressure (p u *) at bottom plate or subfloor level is determined as the greater of the net uplift pressure due to direct uplift on the roof (p u1 *), and the net uplift pressure resultant from the overturning effect of wind pressure on the wall and roof due to lateral wind (p u2 *). The net uplift pressures, p u1 * and p u2 *, are determined as follows: (a) p u1 * = q u (K a C pe + C pi ) 0.8 (G + Q p ) (1) where, K a = 0.8, roof area reduction factor given in AS for areas greater than 100 m 2, assuming that for uplift the house above bottom plate level acts as a rigid box C pe = 0.9, maximum value of external pressure coefficient for uplift C pi = value from Table 5.3 according to wind classification and location where the net uplift is being determined G = dead load resisting uplift from Table 5.4 according to the level where the net uplift is being determined Q p = permanent floor live load resisting uplift from Table 5.4 according to the level where the net uplift is being determined TABLE 5.3 INTERNAL PRESSURE COEFFICIENTS FOR DETERMINATION OF NET UPLIFT PRESSURE Wind classification Location C pi N1 to N4 C1 to C3 Bottom plate level +0.2 Subfloor level 0 Bottom plate level +0.7 Subfloor level 0 NOTE: At bottom plate level, internal pressure on the roof contributes to uplift, whereas for subfloor (either single, upper, or lower storey) the internal pressure on floor and roof equalizes. Standards Australia

105 101 AS TABLE 5.4 DEAD LOAD AND PERMANENT LIVE LOAD RESISTING UPLIFT Single or upper storey Lower storey of two storeys LOCATION Bottom plate level Subfloor level Bottom plate level Subfloor level DEAD LOAD (G), KPA Sheet roof /W Tile roof /W Sheet roof /W Tile roof /W Sheet roof /W Tile roof /W Sheet roof /W Tile roof /W PERMANENT LIVE LOAD (Q P ), KPA (b) [ ( )( ) ( )( )] * Kcqu p = C h C C 0. 75h 2h h h C C 0. 25h + 2 h h h 2 u 2 ptw pe1 pi r r pe2 pi r + W 0.8 (G + Q p ) (2) where K c = 0.8, pressure combination factor applicable where the action effect arises from pressure on two or more surfaces C ptw = combined pressure coefficient for the windward and leeward walls from Table 5.5 according to roof pitch (α) C pe1 = external pressure coefficient for the windward roof slope from Table 5.6 according to roof slope (α) and h/w ratio C pe2 = external pressure coefficient for the leeward roof slope from Table 5.7 according to roof slope (α) and h/w ratio C pi = internal pressure coefficient from Table 5.3 according to wind classification and location where net uplift pressure is being determined h h r = height from lowest floor to single or upper storey ceiling level for single or two storey, respectively = (W/2) tanα, where W is width across the outer walls and α is roof pitch (see Figure 5.1) G = dead load resisting uplift from Table 5.4 according to level where net uplift is being determined Q p = permanent floor live load resisting uplift from Table 5.4 according to level where net uplift is being determined W = overall width across external walls (see Figure 5.1) TABLE 5.5 COMBINED PRESSURE COEFFICIENTS FOR WINDWARD AND LEEWARD WALLS (θ = 0 ) Roof pitch (α) α< α 15 α = 20 α 25 Pressure coefficient (C ptw ) r Standards Australia

106 AS TABLE 5.6 EXTERNAL PRESSURE COEFFICIENTS FOR WINDWARD ROOF areas h/w ratio Pressure coefficient (C pe1 ) Roof pitch (α) < or or or or or or or or or or or or or or or or or or or or +0.2 NOTES: 1 Where two values are given, both values are considered. 2 Values interpolated either between first given values or second given values; not between first and second given values. TABLE 5.7 EXTERNAL PRESSURE COEFFICIENTs FOR LEEWARD ROOF areas h/w ratio Pressure coefficient (C pe2 ) Roof pitch (α) < Standards Australia

107 103 AS C pe1 C pe2 a h r C pi C pi C ptw C pi W C pi h Single or upper storey bottom plate level C pe1 C pe2 a h r C pi C pi C ptw C pi C pi W C pi h Single or upper storey subfloor level C pe1 C pe2 a h r C pi C pi C pi C pi C pi h C ptw C pi C pi W C pi Lower storey of two-storey bottom plate level C pe1 C pe2 a C pi C pi C pi C pi C pi h r h C ptw C pi C pi W C pi Lower storey of two-storey subfloor level FIGURE 5.1 NOTATION Standards Australia

108 AS SECTION 6 PRESSURES FOR DETERMINATION OF RACKING FORCES 6.1 SCOPE AND GENERAL Scope of Section This Section describes how the equivalent pressures tabulated in AS and AS for use with projected areas, for the calculation of racking loads to be resisted by bracing have been derived. The methods of determination of equivalent pressures for the calculation of racking forces in orthogonal directions for single or upper storey, for lower of two storeys and for subfloor level are given Notation Notation symbols for this Section are as follows: H u = height, floor to ceiling for single or upper storey, in metres H L = height, floor to ceiling for lower storey of two storeys, in metres H F = depth of upper floor, in metres W = width of building, in metres (see Figure 6.1) L = length of building, in metres (see Figure 6.1) α = roof pitch, in degrees (see AS and Figure 6.1) θ = wind direction, in degrees (see AS ) h = height to eaves, in metres (see AS ) d = plan dimension of building or part of building parallel to the wind direction, in metres (see AS ) b = plan dimension of building or part of building perpendicular to wind direction, in metres (see AS ) K c = pressure combination factor C pt,roof = combined pressure coefficient for the windward and leeward roof areas C pt,wall = combined pressure coefficient for the windward and leeward walls q u = free stream dynamic gust pressure, in kpa, for the ultimate limit state; values of q u are given in Table B2, Appendix B, for each wind classification Assumptions The following assumptions have been made in the derivation of equivalent pressures for use with projected areas for the determination of racking forces: (a) The geometry assumed is a simple outline of the building, which ignores eaves overhangs, fascias and gutters. The projected area for the roof is taken as the area above ceiling level for the single or upper storey (see Figure 6.1). (b) Buildings are assumed enclosed underneath the lower floor. (c) The floor depth of upper floors (H F ) is assumed to be 0.3 m. (d) H u = H L = 2.4 m. Pressures calculated for 2.4 m floor to ceiling heights are assumed to apply for walls up to 3.0 m high. Standards Australia

109 105 AS (e) (f) (g) A pressure combination factor K c = 0.8 is applied where the load effect is the result of the combination of pressures on two or more surfaces. (K c is not applied in combination with the area reduction factor (K a ).) The assumed combined pressure coefficients for the windward and leeward walls (C pt,wall ) for wind directions θ = 0 and θ = 90 are given in Table 6.1 and Table 6.2, respectively. The assumed combined pressure coefficients for the windward and leeward roofs (C pt,roof ) for wind parallel to the slope (pitch) of roof are given in Table 6.3. Projected areas for determination of single or upper storey racking loads Hips (if hip-ended roof) Ceiling a Floor Ceiling Floor End elevation Side elevation θ = 0 Hips (if hip-ended roof) Ridge L W Plan θ = 90 FIGURE 6.1 NOTATION Standards Australia

110 AS TABLE 6.1 COMBINED PRESSURE COEFFICIENTS FOR WALLS WIND DIRECTION PARALLEL TO ROOF SLOPE* Roof pitch (α) α<10 10 α 15 α = 20 α 25 C pt, wall * For θ = 0 and for hip ends, θ = 90. TABLE 6.2 COMBINED PRESSURE COEFFICIENTS FOR WALLS WIND DIRECTION PERPENDICULAR TO ROOF SLOPE* d/b C pt, wall * For θ = 90 for gable or skillion roof ends. TABLE 6.3 COMBINED PRESSURE COEFFICIENTS FOR ROOFS WIND DIRECTION PARALLEL TO ROOF SLOPE* C pt, roof Ratio h/d Roof pitch (α) < * For θ = 0 and for hip ends, θ = EQUIVALENT PRESSURES ON PROJECTED AREAS For flat wall surfaces, gable or skillion roof ends The equivalent pressure (p) on the projected area shown in Figure 6.2 for calculation of the racking load for bracing in single or upper storey, or the lower of two-storey or subfloor walls is determined from the following equation: p = q u C pt,wall K c (1) where C pt,wall = 1.2, as given in Table 6.2 for d/b = 1 K c = 0.8, pressure combination factor applicable for the combined effect of pressure on two or more surfaces NOTE: The assumption that d = b, i.e. L = W corresponds to the maximum combined pressure coefficient for the walls. Standards Australia

111 107 AS W Wind direction W Wind direction Wind direction W W Wind direction W Wind direction Wind direction W FIGURE 6.2 FLAT WALL SURFACES GABLE AND SKILLION ROOF ENDS For side elevations, single or upper storey, gable or hip-ended roofs The equivalent pressure (p) for the projected areas shown in Figure 6.3 for calculation of the racking load for bracing in single or upper storey walls is determined from the following equation: p = qu Kc [ Cpt,wall (H u / 2) + Cpt,roof (W/2) tan α] (2) where ( H u / 2) + ( W/2) tan α C pt,wall = value from Table 6.1 for roof pitch, α C pt, roof = value from Table 6.3, for roof pitch α, and assuming (h/d) = (H u /W). = 0.8, pressure combination factor K c NOTES: 1 The assumption that h/d = H u /W maximizes the assumed combined pressure coefficients for the roof. 2 The reduction in projected area for hip-ended roofs has been ignored in the determination of the equivalent pressures to be applied to the projected areas corresponding to either hip or gable ended roofs. Wind direction W Wind direction W FIGURE 6.3 SIDE ELEVATIONS SINGLE OR UPPER STOREY GABLE OR HIP-ENDED ROOFS Standards Australia

112 AS Side elevation, lower storey of two storeys or subfloor, gable or hip-ended roof The pressure (p) on the projected area shown in Figure 6.4 for calculation of the racking force for bracing in the lower storey of two-storey walls is determined from the following equation: p = qu Ku[ Cpt,wall ( H u + H F + H L / 2) + Cpt,roof ( W/2) tan α] (3) where ( H u + H F + H L / 2) + ( W/2) tan α C pt,wall = value determined from Table 6.1 for roof pitch (α) C pt,roof = value determined from Table 6.3 for roof pitch (α) and assuming (h/d) = (H u + H F + H L )/W = 0.8, pressure combination factor K c NOTES: 1 The assumption that h/d = (H u + H F + H L )/W maximizes the assumed combined pressure coefficients for the roof. 2 The reduction in projected area for hip-ended roofs has been ignored in the determination of equivalent pressures to be applied for projected areas for either hip- or gable-ended roofs. Wind direction W Wind direction W FIGURE 6.4 SIDE ELEVATION LOWER STOREY OF TWO STOREYS OR SUBFLOOR GABLE OR HIP-ENDED ROOF End elevation, single or upper storey, hip-ended roof The pressure (p) on the projected area shown in Figure 6.5 for calculation of racking loads for bracing in single or upper storey walls is determined from the following equation. p = qu Kc [ Cpt,wall (H u / 2) + Cpt,roof (W/4) tan α] (4) where ( H u / 2) + ( W/4) tan α C pt,wall = 1.2 C pt,roof = value obtained from Table 6.3 for roof pitch (α) with h/d = H u /L and assuming L = W = 0.8, pressure combination factor K c W Wind direction FIGURE 6.5 END ELEVATION SINGLE OR UPPER STOREY HIP-ENDED ROOF Standards Australia

113 109 AS End elevation, lower storey of two storeys, hip-ended roof The equivalent pressure (p) on the projected area shown in Figure 6.6 for calculating racking loads for bracing in walls of the lower storey of two-storey walls is determined from the following equation: qu Kc [ Cpt,wall ( H u + H F + H L / 2) + Cpt,roof ( W/4) tan α] p = (5) ( H u + H F + H L / 2) + ( W/4) tan α where C pt,wall = 1.2 C pt,roof = value obtained from Table 6.3 for roof pitch (α) and assuming h/d = (H u + H F + H L )/L and L = 1.5W = 0.8, pressure combination factor K c W Wind direction FIGURE 6.6 END ELEVATION LOWER STOREY OF TWO STOREYS HIP-ENDED ROOF Standards Australia

114 AS APPENDIX A CHARACTERISTIC BEAM SHEAR STRENGTHS FOR F-GRADES (Normative) The characteristic beam shear strengths for F-grades given in Table A1 have been used for the calculation of beam shear capacity. The adoption of these characteristic beam shear strengths is deemed to satisfy an acceptable level of safety when applied for the design of structural members contained in this Standard. TABLE A1 CHARACTERISTIC BEAM SHEAR STRENGTHS FOR F-GRADES F-grade Characteristic beam shear strengths, Hardwood f s (MPa) Softwood F34 F27 F F17 F14 F F8 F7 F F4 3.1 NOTES: 1 Use of the characteristic beam shear strength values in AS results in some wall plates and continuous span bearers being design critical for shear for spans and loadings for which there has been considerable experience of successful use. 2 It is commonly observed in testing of timber beams that it is difficult to induce a shear mode of failure. 3 In-grade testing of a range of species and grades confirm that the characteristic values for beam shear given in AS for F-grades are conservative. Standards Australia

115 111 AS APPENDIX B WIND CLASSIFICATIONS AND DYNAMIC GUST PRESSURES (Normative) B1 WIND CLASSIFICATIONS The span tables, racking pressures and uplift forces given in this Standard, AS and AS , have been determined for wind classifications (a) N1 to N4 applicable for non-cyclonic regions A and B; and (b) C1, C2, and C3 for cyclonic regions. The wind classifications correspond to bands of design wind speed for the ultimate and serviceability limit state. Wind classifications corresponding to the maximum design wind speeds for the ultimate and serviceability limit states are given in Table B1. TABLE B1 WIND CLASSIFICATIONS Maximum design wind speed (m/s) Wind classification Ultimate limit state Serviceability limit state Non-cyclonic Cyclonic NOTES: 1 The above wind classifications have been adopted from AS AS , AS and AS permit the above classifications to be adopted for design wind speeds up to 5% greater than the maximum values given for each classification. B2 FREE STREAM DYNAMIC GUST PRESSURE The free stream dynamic gust pressure for the ultimate and serviceability limit states for each wind classification given in Table B2 have been calculated in accordance with AS using the maximum design wind speeds given in Table B1. N1 N2 N3 N4 TABLE B2 FREE STREAM DYNAMIC GUST PRESSURES Wind classification Free stream dynamic pressure, kpa Regions A and B Regions C and D Ultimate limit state (q u ) Serviceability limit state (q s ) N N N3 C N4 C C C1 C2 C3 Standards Australia

116 AS APPENDIX C DESIGN OF OVERHANGS FOR PARALLEL BIRDSMOUTH NOTCHED RAFTERS (Normative) C1 GENERAL Rafters are often birdsmouth-notched at their lower support point so as to provide bearing to a wall and to permit an overhang. The following design method, which differs from that given for notches in AS , applies for birdsmouth notches to a maximum depth of one third of the rafter depth. Further, the following design method includes for the load sharing effect obtained when the overhanging ends of parallel rafters are attached to a fascia and the connection and fascia are capable of transferring load to adjacent rafters. C2 EFFECT OF BIRDSMOUTH NOTCH ON RIGIDITY In determining the deflection of the overhanging portion of a birdsmouth notched rafter, the rigidity of the rafter (for both the overhang span and the backspan) is taken as g 47 E r I r, where g 47 is a birdsmouth geometry factor that accounts for reduced rigidity due to the birdsmouth notch and (E r I r ) is the rigidity of the unnotched rafter. The birdsmouth geometry factor is bounded by the range 0.25 g and in this range is given by the following equation: g 47 = 1 (5.7 d notch / L o )... C2 where, d notch = depth of the birdsmouth notch, in mm (see Figure C1) = horizontal span of the overhang, in mm L o d d n d notch d/3 Birdsmouth notch V* M* FIGURE C1 NOTATION AND SIGN CONVENTION Standards Australia

117 113 AS C3 LOAD SHARING FOR PARALLEL RAFTER OVERHANGS In the determination of the strength and serviceability limit states, concentrated and partial area loads (P * and w * ) applied to the overhanging portion of parallel rafters may be assumed laterally distributed to adjacent rafters such that the effective concentrated load (P * eff) or effective distributed load (w * eff) used for the design of an individual rafter may be obtained as follows: P * eff = g 45 P*... C3(1) and w * eff = g 45 w*... C3(2) where P * = design concentrated load w * = design partial area load g 45 = the load distribution factor, which is bounded by the range 0.3 g and in this range is given by the following equation: g 45 h = 0.2 log 10 r hf... C3(3) where h r = g 47 Er I r 3 L o... C3(4) h f = g 47 E r I r E f I f L o, S E f f 3 S I... C3(5) = flexural rigidity of the rafter overhang, calculated in accordance with Paragraph C2 = flexural rigidity of the fascia = horizontal span of overhang and spacing of rafters, respectively C4 RAFTER STRENGTH AT BIRDSMOUTH NOTCH C4.1 Bending Strength The design capacity in bending (φm) at the birdsmouth notch, for the strength limit state, satisfies the following equation: (φm) M *... C4.1(1) where (φm) = φ k 1 k 4 k 6 k 9 [ f b ] Z n... C4.1(2) and M* = design action effect in bending for negative moment as defined in Figure C1 φ = capacity factor given in AS k 1, k 4, k 6 = modification factors given in AS k 9 = strength sharing modification factor for parallel overhanging rafters rigidly connected to a fascia = (S/L o ), but is not less than Standards Australia

118 AS f b = characteristic strength in bending Z n = net section modulus at notch = (bd 2 n /6), where b equals the breadth and d n equals the depth of rafter above the birdsmouth notch (see Figure C1) (d n 2d/3) C4.2 Shear strength at birdsmouth notch The design capacity in shear at the birdsmouth notch for the strength limit state satisfies the following equation: φv V *... C4.2(1) where φv = φ k 1 k 4 k 6 [ f s ] A s... C4.2(2) and V * = design action effect in positive shear (see Figure C1) φ = capacity factor, given in AS k 1, k 4, k 6 = modification factors given in AS f s A s = 3 2 bdn = characteristic strength in shear C4.3 Combined bending and shear (fracture strength) at the birdsmouth notch For a rafter of depth d, birdsmouth-notched to a maximum depth of one third of its depth, as shown in Figure C1, the maximum bending moment action effect (M*) and nominal maximum shear force action effect (V*), calculated for the net section, complies with the following interaction equation: * 2 n n * 6M 6V + φ g50 k 1 k 4 k 6 f sj... C4.3(1) bd bd where b = breadth of the rafter d n = net depth of rafter above the notch φ = capacity factor, given in AS k 1, k 4, k 6 = modification factors given in AS f sj g 50 = characteristic shear strength at joint details = coefficient for birdsmouth notch. = 18/(d ) If, according to the sign convention shown in Figure C1, M * is negative, it may be taken as zero in the application of Equation C4.3(1). Similarly, if V * is positive, it may also be taken as zero in the application of Equation C4.3(1). Standards Australia

119 115 AS AMENDMENT CONTROL SHEET AS Amendment No. 1 (2002) CORRECTION SUMMARY: This Amendment applies to CONTENTS, Tables and 5.2. Published on

120 AS NOTES

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