STD302: Wood Frame Construction Manual 2001 National Edition

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1 AMERICAN FOREST & PAPER ASSOCIATION American Wood Council Engineered and Traditional Wood Products American Wood Council Engineered and Traditional Wood Products STD302: Wood Frame Construction Manual 2001 National Edition A F & P A Copyright American Forest & Paper Association, Inc. All rights reserved. Welcome to the ecourse on the Wood Frame Construction Manual (WFCM) for One- and Two-Family Dwellings, 2001 National Edition. Copyright American Forest & Paper Association, Inc. All rights reserved. 1

2 Copyright of Materials This presentation is protected by US and International copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the American Forest & Paper Association / American Wood Council is prohibited. Copyright American Forest & Paper Association, Inc. All rights reserved. 3

3 STD302: Learning Outcomes By the end of this ecourse, you will be knowledgeable about: 1. The purpose of the 2001 WFCM and its development process 2. Code acceptance and references WFCM document layout 4. Design provisions, including: Shear walls Standard Wall concept Wind load resistance Snow load resistance Seismic load resistance 5. Design Examples for each load type In this ecourse, you will see a brief historical background to the WFCM and its acceptance in the model building codes. The layout of the WFCM documents is described in detail and pertinent provisions for wind snow and seismic loads are discussed. Finally, design examples illustrate how to use various features of the WFCM as well as new design technologies for lateral load resisting wood systems. This edition of the WFCM is a dramatic enhancement of the 1995 WFCM and is applicable nationwide. 4

4 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Snow Wind Seismic Design Examples Snow Design Wind shearwall design Seismic shearwall design Here s the outline for the course. Let s start with the top three topics for background. 5

5 Purpose provide a rational engineering basis and design tools for residential wood frame construction serve applied need for: high wind initially In response to increasing scrutiny of building design and construction in the United States, AF&PA formed a Subcommittee on Conventional Construction (SCC) in 1991, to evaluate emerging state-of-the-art design methods for wood-frame buildings. In areas where existing reference standards and accepted engineering practices were too conservative, or did not exist, research was used to establish new design methods. The first WFCM was developed by AF&PA s Subcommittee on Conventional Construction whose goals were to: - Provide guidelines on residential construction, - Provide technical recommendations on the proper design of residential structures, - Provide technical justification for structural systems, - Prepare residential construction document for reference in model codes and use in design and construction. Hurricane Andrew reinforced the need for the work being done in the high wind area. Northridge earthquake contributed to the need for high seismic provisions. 6

6 WFCM 1995 High Wind Edition guidelines on residential construction proper design of residential structures technical justification for structural systems reference in model codes based on 1991 NDS high wind to SBC In 1996, the SCC completed work on a high wind version of the Wood Frame Construction Manual for One- and Two-Family Dwellings (WFCM). The WFCM contains comprehensive design and construction guidelines for wind-resistant residential wood-frame construction. The document has three distinct parts: general scope and limitations, engineered requirements, and prescriptive requirements. Dead, live and wind loads were all calculated based on the provisions of the 1994 Standard Building Code. Resistance of members, connections, and structural systems were calculated from two sources; the 1994 edition of the Standard Building Code with 1996 Amendments (SBC-96) and AF&PA's 1991 National Design Specification for Wood Construction (NDS ). The SCC examined existing industry recommendations and found areas in design to improve overly restrictive limitations. As a result, two new procedures were proposed and adopted in the SBC-96 and incorporated in the WFCM. These design procedures provide new repetitive member factors for wall studs sheathed with structural sheathing and a perforated shearwall method. A detailed explanation of these changes is available in related literature. Pacific Rim Conference of Building Officials, Wood Frame Construction Manual for Residential Structures,

7 Cost of Compliance using WFCM is favorable Cost of compliance comparison of existing construction methodologies for residential wood structures Prescriptive Analysis One Story Two Story 1995 CABO One- and Two-Family Dwelling Code (Limited high-wind prescriptive requirements) 1994 Standard Building Code (Low wind prescriptive requirements) 1994 Uniform Building Code (Low wind prescriptive requirements) Wood Frame Construction Manual (High wind engineered prescriptive requirements) $4,655 $11,144 $4,500 $9,123 $4,584 $9,256 $4,929 $10,260 Engineered Analysis One Story Two Story ASCE 7-95 $7,849 $14, Standard Building Code $5,454 $11,492 The National Association of Home Builders Research Center analyzed the associated costs of compliance with the WFCM compared to other national recognized codes and standards. The study evaluated the costs of constructing structural elements for two generic homes, containing typical construction characteristics, using prescriptive provisions of the 1995 CABO One- and Two-Family Dwelling Code; the 1994 Uniform Building Code (UBC); the 1994 Standard Building Code (SBC 94); and the WFCM. The report also compared the cost of these four prescriptive design methods to engineered designs using load requirements of ASCE 7-95, Minimum Design Loads for Buildings and Other Structures (ASCE 7), and the SBC 94. The National Association of Home Builders Research Center, The State_of_the_Art of Building Codes and Engineering Methods for Single_Family Detached Homes: An Evaluation of Design Issues and Construction Costs, June 1997 The report concluded that, The WFCM appears to embody the most economical, engineering-based prescriptive construction requirements for residential construction in high wind conditions. This report also confirmed that the WFCM offers engineering-based solutions that are cost competitive with prescriptive code requirements and offers substantial savings over pure engineering analysis, particularly as required by ASCE 7. 8

8 WFCM 2001 The New National Edition based on 1997 NDS updated for: all wind snow seismic for one- and two-family wood frame dwellings nationally AF&PA s American Wood Council is a nationally-recognized Standards Writing Organization which follows the standard-development guidelines of the American National Standards Institute (ANSI). AF&PA maintains and publishes the NDS, the nationally-recognized design standard for wood construction. The NDS is referenced by the three U.S. model building codes and numerous other codes and standards currently enforced throughout the United States. NDS provisions provide designers with the state-of-the-art practice on structural wood and connection design. WFCM - The New National Version AF&PA has currently released the WFCM 2001 edition. An ANSI Canvass Committee was established with representation by manufacturers, regulators and users. Consensus on WFCM 2001 provisions was prior to publication. The goals for publishing the WFCM 2001 were to: - develop national consensus on design of wood frame one and two-family dwellings in high wind, seismic and snow zones; - provide a forum for the introduction of new and innovative design methodologies for one and two-family wood-frame dwellings; - provide national education on design of one and two-family wood frame structures; - create a national forum to introduce design changes resulting from analysis of natural disaster surveys. 9

9 Model Code Acceptance 2003, 2006 IBC 2003, 2006 IRC 2003 NFPA The WFCM 2001 is recognized by the following model building codes in the U.S.: 2003 and 2006 IBC International Building Code 2003 and 2006 IRC International Residential Code 2003 NFPA 5000 Building Construction and Safety Code 10

10 ASCE 7-98 Load Reference 2001 WFCM calibrated to work with ASCE 7-98 Loads The WFCM 2001 is calibrated to work with ASCE 7-98 loads and maps. This is important no other load document should be used with the 2001 WFCM. 11

11 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Snow Wind Seismic Design Examples Snow Design Wind shearwall design Seismic shearwall design Now let s explore the WFCM a little to get familiar with it. 12

12 WFCM 2001 WFCM 2001 is a 2 part document: the Manual contains the standard and the WFCM Commentary contains background information and example calculations. 13

13 Manual Overview/Contents Chapter One General Information Chapter Two Engineered Design Chapter Three Prescriptive Design Supplement Commentary The primary WFCM volume comprises three chapters with an accompanying supplement containing design values and other useful information. The second volume Commentary provides complimentary explanation and detailed calculation examples for the WFCM provisions. 14

14 WFCM Layout 1 General Information 2 Engineered Design 3 Prescriptive Design Supplement The manual is laid out in three chapters: general information, engineering design, and prescriptive design; and the supplement. But the WFCM is worked as follows: Chapter 1 to see if your project will qualify under the WFCM provisions, then Chapter 3 to design approximately 80% of the structural elements in your house, then Chapter 2 to design the next 10 to 15% of the elements, and lastly anything left (typically about 5%) will need to be designed with current NDS provisions. Organizing yourself in this fashion will optimize the time needed to design the house and dramatically increase your efficiency. Now let s see what s in each chapter. 15

15 1 General Information Background material for manual definitions terminology symbols what? Chapter 1 General Information gives definitions, terminology explanations, and symbolic representations that apply to the remaining chapters and the manual. 16

16 1 General Information Scope Definitions Referenced standards Applicability limitations The scope and limitations of the applicability of the manual to your project is described. Here are some of them: 17

17 1 General Information - Limitations h R Stories / Mean Roof Height (MRH) h /2 R 3 Stories or less MRH = 33' G MRH G/2 DETERMINING NUMBER OF STORIES ABOVE THEFOUNDATION O N E S T O R Y T W O S T O R Y T H R E E S T O R Y >6 MRH >6 MRH >6 MRH - Foundation per section MRH - Measured from average grade MRH MRH MRH Limitations on building dimensions including mean-roof-height (MRH), # of Stories, and aspect ratio that must be met in order to use the WFCM. Applications outside the prescribed limits require design per AF&PA s NDS or LRFD standards, or other code approved means. Figures such as this one are included to help the user interpret design limitations. The Figure illustrates the definition of MRH and # of Stories as used in the WFCM. Roof Slopes > 6:12 are considered as another story above the foundation. 18

18 1 General Information - Limitations Vertical floor offsets Shearwall plan offsets CONNECT AS NEEDED TO TRANSFER SHEAR OFFSET NOT > d d SHEARWALL SHEARWALL OFFSET BLOCKING SHEARWALL WFCM Figures are included to help the user interpret limitations on vertical floor offsets and shearwall plan offsets. 19

19 1 General Information - Limitations Irregular Structures LATERAL LOAD DIRECTION STRUCTURE WITH OFFSET GREATER THAN 4 FEET > 4' > 4' Option #1 Option #2 SEPARATE STRUCTURES Building 1 Building 2 INSCRIBED STRUCTURE Building 1 Building 3 Building 1 > 4' > 4' > 4' Building 2 Building 3 Building 1 Guidance for designing irregular structures as separate structures or inscribed is provided. The inscribed structure option is used for wind loads only, while the separate structures option can be used for both wind and seismic loads. 20

20 1 General Information - Limitations Inscribed Structure Method for Wind loads only inscribe overall building into one rectangle The inscribed structure method, applicable for wind loads, is a means of facilitating the calculation of shear wall sheathing lengths where building geometry is non-rectangular - by inscribing the overall building into one rectangle. 21

21 1 General Information - Limitations Separate Structure Method for Wind and Seismic loads in-story wall offsets > 4 ft split into rectangular structures and determine sheathing requirements for walls in each shared wall sheathing amount is the sum of shear wall sheathing lengths for each separate structure at that location (Wall A) Where wall offsets exceed 4 feet within a single story, rectangular portions of the structure are to be considered as separate structures in accordance with Section c. Sidewall and endwall shear wall sheathing lengths are determined based on the geometry of each separate structure comprising the overall building. Where wall lines are shared, such as Wall Line A, the shear wall sheathing amount for the wall line is taken as the sum of shear wall sheathing lengths for each separate structure at that location. 22

22 1 General Information - Limitations Inscribed Method - in-story wall offsets > 4 ft use inscribed tributary area within dotted lines to provide a balanced shear wall layout (as per separate colors shown) shear wall sheathing lengths are based on MWFRS loads Bracing lengths be determined in accordance with the inscribed method where wall offsets are greater than 4 feet within a single story. As noted in Section c, determination of shear wall sheathing length based on the overall inscribed building dimension is permitted for wind. Shear wall sheathing lengths can be determined using the inscribed area as shown (in dotted lines). Distribution of required shear wall sheathing lengths, as shown in Figure 3, based on tributary area for each wall line provide a balanced shear wall lay-out. For example, the thicker purple line shows the tributary wall area to be used (in plan) for designing the shear wall shown in purple. Similarly the same holds true for the tributary areas and shear walls shown in green and orange. Note that shear wall sheathing lengths are based on MWFRS loads. Localized components and cladding (C&C) loads on roof surfaces, rafters, dormers, etc. are handled in other tables of the WFCM. 23

23 1 General Information - Limitations In-story wall offsets < 4 ft use either inscribed method or separate structures method for such small offsets, distribution of shear wall sheathing lengths based on tributary area is not required where the inscribed method is used WFCM assumption: diaphragms in accordance with WFCM provisions are capable of maintaining load path to supporting elements below where offsets are small Both the inscribed method and separate structures method are permitted where walls are offset by less than 4 feet within a single story. For such small offsets, distribution of shear wall sheathing lengths based on tributary area is not required where the inscribed method is used. In the WFCM, it is assumed that diaphragms in accordance with WFCM provisions are capable of maintaining load path to supporting elements below where offsets are small. 24

24 1 General Information - Limitations Inscribed Method - in-story wall offsets > 4 ft and ridge lines not parallel use inscribed structure method and conservatively determine sheathing lengths assuming wind is perpendicular to ridge (WFCM Table 3.17A) The inscribed structure method can be used but required shear wall sheathing lengths should be conservatively determined assuming wind is perpendicular to the ridge (see WFCM Table 3.17A). 25

25 1 General Information - Limitations For more information, see: DA5: Inscribed versus Separate Structures in the WFCM Free download from For more information, see Design Aid 5 which was developed as supplemental information for the 2001 WFCM to better the understanding of the design of inscribed versus separate structures. 26

26 1 General Information - Limitations Aspect Ratios L 2 L L 1 <4 L / L 1 2 O 2 < Lesser of 12 ft or L 2 / 2 O 1 < Lesser of 12 ft or L 1 / 2 H L 2 H / L < 3 1 / 2 L 1 Exterior walls adjacent to the opening shall be framed using full height studs, where the opening is less than 2ft. from the exterior wall. Here are some more limitations found in Chapter 1: Floor and roof diaphragm aspect ratios, shearwall segment aspect ratios, and floor diaphragm opening limits. We ll talk about these more later. 27

27 2 Engineered Design minimum loads for establishing specific resistance requirements results of engineering calculations for specific elements, in specific configurations, under specific loads tabulated information a significant time saver for the busy design professional Chapter 2 contains a set of engineered requirements, reiteration of importance of maintaining load path, applicability limits that apply to use of Chapter 2, and enabling language for design values in the WFCM Supplement. 28

28 2 Engineered Design - Limitations Specifically outlines applicability of engineering provisions Here are the limitations as found in the WFCM that apply to the use of Chapter 2, and guidance once limitations are exceeded. 29

29 2 Engineered Design General Provisions Connections Floor Systems Wall Systems Roof Systems Tables Figures Chapter 2 is presented in terms of assembly systems, beginning first with connections. The manual is profusely illustrated with helpful diagrams and 3D detail drawings for common standard assemblies. 30

30 2 Engineered Design Lateral Loads FLOOR JOIST LATERAL FRAMING LOADS STUD FLOOR JOIST WFCM Table 2.1: Calculated loads to be resisted with lateral framing connections. 31

31 2 Engineered Design 2001 WFCM wind load tables have been enhanced from the 1995 SBC edition to include broader range of wind speeds and a better understanding of wind pressures acting on various building surfaces. This example shows the table for Roof and Wall Sheathing Suction Loads for 3 second gust speeds from 85 to 150 mph. The building surface is zoned into 6 areas, with a corresponding pressure for a given wind speed. 32

32 2 Engineered Design Suction Loads Designing for suction loads is critical. Hip and gable roof examples show panels lost at edges in high wind roof zones. Nailing patterns are critical in high wind zones. This nailing pattern didn't meet code minimums, which led to breach of the structure during a hurricane (Andrew). 33

33 2 Engineered Design Results of Sheathing Loss Once sheathing is lost, progressive failures of other components follow. Content damage is the most expensive result. 34

34 2 Engineered Design Cantilever limits JOISTS SHALL BE LOCATED DIRECTLY OVER STUD UNLESS TOP PLATE IS DESIGNED TO CARRY THE LOAD LOADBEARING WALL or SHEARWALL REQUIRED BLOCKING d BAND JOIST L MAX. d * * See Exception NON-LOADBEARING NON-SHEARWALL REQUIRED BLOCKING BAND JOIST JOISTS SHALL BE LOCATED DIRECTLY OVER STUD UNLESS TOP PLATE IS DESIGNED TO CARRY THE LOAD L MAX. L / 4 WFCM has limitations on cantilevers as shown in these figures. WFCM span table values will apply up to these limits. 35

35 2 Engineered Design LOADBEARING WALL OR SHEARWALL REQUIRED BLOCKING d BAND JOIST Setback limits JOISTS SHALL BE LOCATED DIRECTLY OVER STUD UNLESS TOP PLATE IS DESIGNED TO CARRY THE LOAD L LOADBEARING WALL or SHEARWALL REQUIRED BLOCKING MAX 4d WHEN DESIGNED FOR ADDITIONAL LOAD MAX. d d JOISTS SHALL BE LOCATED DIRECTLY OVER STUD UNLESS TOP PLATE IS DESIGNED TO CARRY LOAD Similarly, WFCM has limitations on setbacks, to which span table values are limited to. This is a simple way of dealing with specific loading for specific configurations. 36

36 2 Engineered Design JOISTS BLOCKING SECTION A-A ENDWALL Endwall blocking A A BLOCKING Endwall blocking details are very critical to ensure load transfer from endwalls into a horizontal ceiling diaphragm by providing a nailing surface. 37

37 2 Engineered Design Hold down calculations V V h Rotation T L v v = V/L T = v*h V = Lateral Load (lbs) v = Required Unit Shear Capacity (plf) T = Required Holddown Capacity (lbs) Overturning details and holddown calculations are also provided for shearwalls. More on this, later. 38

38 2 Engineered Design 4" o.c. Nail Spacing Connection per Section & L 4' Perimeter Zone panel field nailing 4' Perimeter Zone panel edge nailing Lesser of L/2 or 2' Blocking 2x6 Outlooker (2x4 minimum) A Gable Endwall A Section A-A Rake details - outlookers End framing of gable roofs can be addressed using outlookers and WFCM has rake overhang limits. 39

39 2 Engineered Design 4" o.c. Nail Spacing 4' Perimeter Zone panel field nailing 4' Perimeter Zone panel edge nailing < 1' Lookout Block Gable End Truss or Endwall A Section A-A A Rake details - ladder Another alternative is the popular lookout blocks (ladder frame), and WFCM has rake overhang limits. 40

40 2 Engineered Design Consequences of inadequate rake details If rake overhangs are not properly detailed, the building may be breached. 41

41 2 Engineered Design Enhancements from 1995 WFCM covers lower wind speeds new snow loads new seismic loads SBC loads 2000 IBC loads (ASCE 7-98 with amendments) The chief enhancements in Chapter 2 from the 1995 to the 2001 WFCM are as a result of the national scope of the document: wind speeds across a broad spectrum snow loads seismic loads all consistent with 2000 IBC (ASCE 7-98 with amendments). For example, the WFCM 2001 assumes an enclosed structure; other enclosures are not tabulated. 42

42 3 Prescriptive Design specific set of resistance requirements for residential buildings Chapter 3 contains prescriptive design information intended for use by builders and lay people. Similar in information content to Chapter 2, but conveyed in a different way. 43

43 3 Prescriptive Design Prescriptive Design General Provisions Connections Floor Systems Wall Systems Roof Systems Tables Figures Chapter 3 contains prescriptive solutions based on Chapter 2 engineered provisions and follows the same format as Chapter 2 including connections, floors, walls, and roofs. 44

44 3 Prescriptive Design - Limitations Specifically outlines applicability of prescriptive provisions Based on minimum prescriptive design limitations in model building code provisions Once again, limitations are imposed on the use of the provisions within this chapter and are described right at the very beginning. Guidance is given if limitations are exceeded - often reference is made back to Chapter 2. 45

45 3 Prescriptive Design Sidewall Sheathing AMENDED ENDWALL SIDEWALL WFCM - Table 3.6B shows one table for sidewall sheathing length requirements for traditional shearwalls in wind exposure B. 46

46 3 Prescriptive Design Full height sheathing length for end walls and sidewalls, Tables 3.17A and B, pages Additional tables cover endwalls, segmented shearwalls (Type I), and perforated shearwalls (Type II). 47

47 3 Prescriptive Design Framing to Foundation Details WFCM - Figures 3.2a-c: Sill and Bottom Plate anchorage to the foundation. Foundation design is beyond the scope of WFCM, but detailing anchorage requirements is not. 48

48 3 Prescriptive Design Notching Limits Outer third of span only Outer 1/3 of span only Notch depth < 1/4d d Hole edge distance > 5/8" Stud Hole diameter < 2/5d Single Stud 1/4 Joist depth, Max. 1/3 Joist depth, Max. 2" Min. Hole diameter < 3/5d Double Stud 1/3 Joist depth, Max. 1/6 Joist depth, Max. Plate Hole edge distance > 5/8" WFCM - Figures give notching and boring limitations for joists, rafters, and studs. 49

49 3 Prescriptive Design Stud Moisture-Resistant Drywall Floor Framing Details Bottom Plate Stud Subflooring Band Joist Bathtub Joist Block Double Plate Stud Stud Double Trimmer Joist Subflooring Plate Subflooring Joist Stud Blocking Band Joist Double Plate Joists shall be located directly over studs as well as common framing details for things such as joists framing on a stud wall, cantilevered joists, and framing for concentrated loads like a bath tub. 50

50 3 Prescriptive Design Rafter/Collar Ties Rafter Ridge Board Collar Tie (Collar Beam) (Located in upper third of attic space)(see ) Ridge Board Rafter Tie (Located in lower third of attic space) Rafter Collar Tie (Collar Beam) (Located in upper third of attic space) (see ) Ceiling joist parallel to rafters WFCM - Figures give clarifications of Ridge Board vs. Ridge Beam and Rafter Tie vs. Collar Tie. 51

51 3 Prescriptive Design Gable End Bracing 2x4 Continuous lateral brace at 6' o.c. Truss or Ceiling Joist 2-10d Nails Gable End Truss 10-8d Nails 5d Cooler Nails at 10" o.c. 2"x4" Block nailed to each brace with 4-10d nails Gypsum Board 5d Cooler Nails at 7" o.c. 20 Gage Strap 10-8d Nails Endwall Studs Ceiling bracing gable endwall - very important detail to ensure that a hinge does not form between gable end trusses and gable end stud walls. This is a typical failure seen in hurricanes. 52

52 3 Prescriptive Design Hold down Details Blocking at 24" o.c. allows holddown installation Sidewall 1/2" Spacing allows holddown installation Holddown Endwall Corner stud connected to transfer shear 2-16d Common nails at 6" o.c. Holddown 2-16d Common nails at 10" o.c. Corner stud connected to transfer shear Some typical holddown details. Note the nailing detail for where the wall end studs meet. This is often the most overlooked connection on a house and one of the most critical to the structure s integrity. 53

53 3 Prescriptive Design Connections nails - minimum limits Chart values invalid! Minimum prescribed nailing provisions are tabulated.but then, if the nails miss the studs as in this picture, you can forget about the table. 54

54 3 Prescriptive Design Connections bolted anchorage FRONT DOOR STEP Guidance is given on structural anchorage in prescriptive form to hopefully prevent homes from becoming roller-skates under wind loads. 55

55 3 Prescriptive Design Enhancements from 1995 WFCM updated with information from 1997 NDS tables based on Wind Exposure B, with Appendix for Wind Exposure C national version in accordance with 2000 IBC/IRC ANSI approved The 2001 WFCM prescriptive provisions have been updated with design information from the 1997 NDS. Wind tables are based on exposure B, however and Appendix for wind exposure C information has been included. All of the information in the prescriptive provisions is national in scope and ANSI approved (consensus basis). 56

56 Supplement 1 General Information 2 Engineered Design 3 Prescriptive Design Supplement The supplement is the last segment in the WFCM. 57

57 Supplement 1A 1B & 1C 2A & 2B 2C 3A 3B 4A - 5C Nominal and Dressed Sizes of Sawn Lumber Section Properties of Sawn Lumber and Glulam Sheathing Spans for Floor and Roof Sheathing Shear Capacities for Horizontal Diaphragms Sheathing Spans for Wall Sheathing Design Criteria and Capacities for Shearwall Materials Framing Member Design Values 6 &7 Nail Connection Capacities The Supplement contains design values needed for engineered design. It is located at the end of the WFCM manual, not in the Commentary volume. It s based on 1997 NDS Supplement with the addition of Tables 2A-C, 3A&B, 6, and 7. 58

58 WFCM 2001 Commentary - Layout 1 General Information 2 Engineered Design 3 Prescriptive Design Supplements The WFCM Commentary contains background information and example calculations. 59

59 WFCM 2001 Commentary Background information and calculation procedures used in development of WFCM General Information Engineered Design Prescriptive Design It provides the user with assumptions used in development of each table, derivations, and sample calculations for each table. 60

60 WFCM 2001 Commentary Detailed explanation Example calculations with graphics Here is an example page from the commentary highlighting detailed information, calculation procedures, and graphics to facilitate understanding. 61

61 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Snow Shear walls Standard Shear Wall Wind Seismic Design Examples We have seen some of what is in the WFCM and how the manual is presented in terms of the engineering, and prescriptive approaches. Next we ll take a quick look at some of the 2001 provisions categorized by load type. First, we ll begin snow load (a gravity load) and how the WFCM address snow. The we ll address lateral loads and resistance with a discussion on shearwalls, then a combined discussion of load resistance behavior with WFCM provisions for each of wind and seismic loads. 62

62 WFCM 2001 Provisions - Snow per 2000 IBC provisions psf ground snow load unbalanced snow loads considered in tables Let s turn our attention first to snow issues. It snows in various regions of the country, and 30 to 70 psf ground snow load provisions are included in the 2001 WFCM. Snow load span tables automatically reflect the consideration of unbalanced snow loads. 63

63 WFCM 2001 Provisions - Snow Ground snow load contours Snow loads are shown in psf Snow loads at higher elevations are shown in parentheses IBC Figure 1608 IBC Figure 1608 presents ground snow loads in the US. Some states and municipalities may have their own snow load maps and provisions that the designer should be aware of. 64

64 Snow Issues If rafters are not properly designed and constructed, the weight of snow can cause damage. Rafters can deflect excessively Rafters can spread, causing excessive loads on exterior walls Rafters can fail and collapse. 65

65 WFCM 2001 Provisions - Snow found in Chapter 2 by wood strength and stiffness properties As an example, span tables for rafters subjected to snow loads in chapter 2 (engineering) are ordered by wood strength and stiffness parameters familiar to technical wood designers... 66

66 WFCM 2001 Provisions - Snow and in Chapter 3 by wood grade and species group while the same information is presented in Chapter 3 (prescriptive) by the more userfriendly wood grade and species group that easily be correlated to wood grade stamps found on each piece of construction lumber. 67

67 WFCM 2001 Provisions - Snow and in Chapter 3 for panel selection for snow Panel information is provided in Table 3.12B for Rood Live and Snow loads... 68

68 WFCM 2001 Provisions - Snow and in Chapter 3 for panel selection for floor live and Table 3.14 for Floor Live Loads. 69

69 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Snow Shear walls Standard Wall Wind Seismic Design Examples Now let s look at the topic of shearwalls. The WFCM emphasizes completeness of load path, and shearwalls are one of the key elements used to do this. 70

70 Shearwalls a lateral resistance device Load Path This is a graphical illustration of how wind load moves through various building assemblies and gets transferred into the ground: first, the windward wall; which transfers in-plane load to the roof diaphragm; which transfers reaction loads to the tops of the side shearwalls; which transfer load into the ground. Note the important components: the windward wall, the roof diaphragm, and the side shearwalls with associated shear and hold-down anchorage devices. 71

71 Resisting Elements - Shearwalls racking resistance perimeter nailing sliding resistance Shearwalls are a vertical building element that can resist lateral forces applied at the top of the wall. In a wood shearwall, the panel perimeter nails provide the bulk of the racking resistance through wood bearing and nail deformation when the lateral external force is applied. Horizontal wall sliding is resisted by nailing or other anchorage installed along the bottom of the shearwall sufficient to resist the external lateral force. 72

72 Resisting Elements - Shearwalls panel aspect ratio racking action cantilever beam action In order to make this concept work, panels must have a height-to-width aspect ratio of less than 3.5 to 1. This ratio is sufficient to develop racking action in the shearwall panel. Aspect ratio s greater than this produce cantilever beam action - a completely different behavior that is much less effective in resisting lateral forces. 73

73 Resisting Elements - Shearwalls Five parts of a shearwall wood structural panels wood frame nails hold downs plate anchors The shearwall is a device which has five essential components to make it complete: -- a wood frame, -- wood structural panels: the brace, -- nails: perimeter nails to resist the racking moment, and field nails to resist wind suction and panel separation from the frame, -- plate anchors: to resist sliding due to applied horizontal force, and -- hold downs: to stop the wall panel from in-plane overturning. The perimeter nails are key to making this device work to design lateral load. Their ability to repeatedly distort under load over many cycles to dissipate energy makes them a vital component. 74

74 Wall Sheathing Fasteners Center-Point Bending Test Load Nails low / medium carbon steel ASTM F1667 NDS Table I1 F yb values Roofing Nails (WFCM Table3.1 note 3) Corrosion resistant 11 gage Check IBC for additional requirements Staples (WFCM Table3.1 note 3) Corrosion resistant 16 gage Check IBC for additional requirements Since the nails repeatedly distort so much while dissipating the racking energy over a significant period of time; it is very important that they be made of a ductile, but strong, metal so they can do their job without failing. The WFCM requires nails of low to medium carbon steel for this purpose a steel that is known to be ductile. High carbon steels as found in some fasteners fail in a sudden brittle manner, often with very little repetitive distortion. Note that roofing nails and staples referenced in the WFCM need to be of the indicated gage, as well as be corrosion-resistant. The IBC has more information on this requirement. 75

75 Resisting Elements - Hold Downs overturning Finally, overturning may be a problem, especially for high aspect ratios. These skinny panels usually develop high overturning forces at the bottom corners of the walls that need to be resisted with the installation of special hold-down hardware. 76

76 Standard Shear Wall Assembly details for these panels as described in 2001 WFCM d common 6 OC on panel perimeter 8d common 12 OC in field 7/16 wood structural panel continuous height over wall plates panel exterior 5d cooler 7 OC on panel perimeter 5d cooler 10 OC in field 1/2 gypsum wallboard on interior panel interior Here are the wall assembly assumptions used for the development of the preceding methodology. A cooler nail is also known as a drywall nail. For discussion purposes, we ll call this assembly the standard shearwall. It s actually the base case shearwall that the WFCM is created around. 77

77 Length of Wall Concept More perimeter nails = shorter wall length for same applied lateral load p p 6:12 perimeter:field nailing pattern = 3:12 perimeter:field nailing pattern Length of wall Length of wall The length of wall concept is used in the WFCM as a measure of the unit shear capacity of the shearwall. By decreasing the perimeter nail spacing, more wall racking resistance is provided. Thus for the same load p, the required wall length would shorten because of the increased number of perimeter nails. 78

78 Length of Wall Concept More perimeter nails = more load resistance for same wall length p P++ 6:12 perimeter:field nailing pattern = 3:12 perimeter:field nailing pattern Length of wall Length of wall Another way of expressing this is as follows. If the wall length remains constant, and more load capacity is required (P++), simply increase the number of perimeter nails in the shearwall (decrease the panel perimeter nail spacing). 79

79 Wall Design Modification Alternative assembly details for these panels are available from Table 3.17D which accordingly modify the wall lengths with factors. 8d common 6 OC on panel perimeter 8d common 12 OC in field 7/16 wood structural panel continuous height over wall plates panel exterior Modified wall length = standard wall length x Table 3.17D factor (wind or seismic) The WFCM makes this concept work very easily in Table 3.17D. The Table takes the standard shearwall as the base case, with seismic and wind modification factors as 1.0. Depending on the desired assembly listed in the table, seismic and wind modification factors respectively can be used to modify the required base case wall length. The Table also lists the unit shear capacities of the various wall assemblies. We ll see a numerical example of this implementation a little later. 80

80 Shearwall Design Methodologies Safety Factor Adjustments Summing Dissimilar Shearwall Materials Perforated Shearwall Method System Factors for Stud Walls Much of the shearwall design methodologies presented in this ecourse are as adopted by the SBC, and based on AF&PA s National Design Specification (NDS ) for Wood Construction 1997, national and international research, and reevaluation of existing practice. 81

81 Safety Factor Adjustments Issues: Requires higher safety factor shear walls and diaphragms Solution: Adjusted safety factor to generally acceptable level AF&PA s Subcommittee on Conventional Construction (SCC) looked at safety factors associated with wood structural panel (WSP) shearwall & diaphragms design and felt they were more conservative than for other materials, therefore they were adjusted to a more generally acceptable level 82

82 Safety Factor Adjustments Shear Capacities for Shear walls & Diaphragms: increased by 40% for wind design based on an adjustment of the minimum load factor from 2.8 to 2.0 IBC (diaphragms) IBC (shearwalls) Effect of adjustment was 40% increase in shear capacity of Wood Structural Panels (WSP) for wind design. 83

83 Shearwall Design Methodologies Safety Factor Adjustments Summing Dissimilar Shearwall Materials Perforated Shearwall Method System Factors for Stud Walls 84

84 Summing Dissimilar Shearwall Materials Issues: Ignores the contribution of interior wall sheathing Solution: Develop procedure which recognizes the contribution of interior sheathing materials A second concern was that current practice ignored contribution of interior sheathing (gypsum), therefore the SCC developed a procedure to recognize added shear capacity of interior sheathing. 85

85 Summing Dissimilar Shearwall Materials The allowable shear capacity of a shear wall segment sheathed on both sides, with similar or dissimilar materials, shall equal the sum of the individual shear capacity of each side IBC wind applications only! The shear capacity of a shearwall segment sheathed on both sides to resist wind loads only is additive. 86

86 Summing Dissimilar Shearwall Materials Substantiating Test Data FPL - Predicting Racking Performance of Walls Sheathed on Both Sides FPL - Racking Performance of Light-Framed Walls Sheathed on Two Sides FPL - Contribution of Gypsum Wallboard to Racking Resistance of Light Frame Walls Forintek - Lateral Resistance of Nailed Shear Walls Subjected to Static and Cyclic Displacement APA - Report Wood Structural Panel Shear Walls with Gypsum Wallboard and Window/Door Openings Various sources used in development and substantiation of this procedure. 87

87 Summing Dissimilar Shearwall Materials APA Wall Tests Wall #1-15/32" plywood only applied vertically Blocked with 8d 3" (edge) and 12" (field) Wall #2-1/2" gypsum only applied horizontally Unblocked with 5d 7" (edge) and 7" (field) Wall #3 - Sheathing from Wall #1 and Wall #2 on opposite sides APA tested 3 walls: WSP only, gypsum only, and a combination of the two. 88

88 Summing Dissimilar Shearwall Materials APA Wall Tests Wall Existing Tabulated 1.4 x Tabulated Tested Number Shear Capacity (plf) Shear Capacity (plf) Shear Capacity (plf) # (a) 1680 # (b) 254 # (c) 2040 (a) Using safety factor adjustment of 1.4. (450 * 1.4) = 630 (b) No adjustment was taken on gypsum wallboard shear capacities. (c) Proposed allowable design capacity. (450 * 1.4) = 730 Results show shear capacity of each wall using traditional shear capacities and procedure, compared to adjusted shear capacities and addition of interior sheathing. Walls tested show 2-3 times greater capacity than these methodologies allow for. Note that Wall #3 exceeds the sum of Walls #1 and #2. 89

89 Shearwall Design Methodologies Safety Factor Adjustments Summing Dissimilar Materials Perforated Shearwall Method System Factors for Stud Walls 90

90 Perforated Shearwall Method Issues: Requires numerous interior hold downs for shear walls Solution: Eliminate need for interior hold downs by reducing effective shear capacity of wall assembly The third design methodology was developed because of numerous holddowns required on shearwall segments, which creates a challenge both in installation and in maintaining load path. Current practice is valid, however a method was needed to eliminate some of the interior holddowns. 91

91 Segmented Shearwall Method An example of the traditional shearwall method shows that 6 holddowns and enough mass in the foundation would be required to prevent overturning of these typical wall segments. 92

92 Perforated Shearwall Method In this example, the perforated shearwall has a reduced shear capacity from the traditional, but interior holddowns have been eliminated. 93

93 Perforated Shearwall Method Substantiating Test Data: Professor Hideo Sugiyama 12 studies in Japan over a period of 20 years APA - Report 157 Wood Structural Panel Shear Walls with Gypsum Wallboard and Window/Door Openings Virginia Tech Monotonic and Cyclic Tests of Shear Walls with Openings NAHB - RC Monotonic and Cyclic Tests of Shear Walls with Openings Three sources were used in development and substantiation of perforated shearwalls, including Sugiyama, APA-The Engineered Wood Association, Virginia Tech and NAHB Research Center tests. 94

94 Perforated Shearwall Method Test data closely matches design procedure Correlation of test data from these studies to the perforated shearwall method is very good and conservative. 95

95 Perforated Shearwall Method Maximum Unrestrained Opening Height (Window or Door Height) 8' Wall 10' Wall Percent Full-Height Sheathing 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 2'-8" 4'-0" 5'-4" 6'-8" 8'-0" 3'-4" 5'-0" 6'-8" 8'-4" 10'-0" Effective Shear Capacity Factor IBC In the Perforated Shearwall Method, shear capacity is reduced using these effective shear capacity factors, adopted into the Standard Building Code. Critical factors in this table are percent of full height sheathing, and maximum unrestrained opening height. 96

96 Traditional (Segmented) Shearwall Method 2884# 3360# 5:12 Roof Slope 36' 4' 2-1/2' 2-1/2' 2-1/2' 5-1/4' 2-1/2' 5-1/4' 2-1/2' 2-1/2' 2-1/2' 4' 4' 5' 4' Required Capacity = 2884lbs/13ft = 222 plf 15/32" WSP (8d at 6/12) SPF Framing (G = 0.42) Tabulated Capacity = 230 plf Shearwall Capacity = 230 plf * 13 ft = 2990 lbs Holddown Capacity = 230 plf * 8 ft = 1840 lbs 2840 lbs 4680 lbs Base Shear = 6244 lbs 4680 lbs Required Capacity = (2884lbs lbs)/21ft = 297 plf 15/32" WSP (8d at 4/12) SPF Framing (G = 0.42) Tabulated Capacity = 355 plf Shearwall Capacity = 355 plf * 21 ft = 7455 lbs Holddown Capacity = 355 plf * 8 ft = 2840 lbs unadjusted shear capacities To demonstrate the effects of each of these three shearwall design methodologies. First look at an example of the traditional shearwall using the unadjusted shear capacities. Note that a dozen holddowns are required along the length of the first floor. The WFCM uses 60% of the dead load to resist wind uplift. In most cases, the wind uplift is much greater than 60% of the dead load, and will require more than the dead load alone to offset the wind force component. For seismic loads, the holddowns are conservatively sized in the WFCM to meet the shear capacity of the shearwall. 97

97 Traditional (Segmented) Shearwall Method TABLE 3B - WOOD STRUCTURAL PANEL SHEAR CAPACITIES FOR SHEARWALL ASSEMBLIES Framing Species G $ 0.49 Framing Species 0.49 > G $ 0.42 Panel Edge Nail Spacing (in.) Framing Species G < Sheathing Material Sheathing Thickness (in.) Nail Size Recommended Shear Capacity (plf) 1 Structural I 5/16 6d /8 8d , /16 8d , /32 8d 10d Structural Sheathing 5/16 6d /8 6d 8d , /16 8d , /32 8d 10d /32 10d Plywood Siding 5/16 6d /8 8d WFCM 1997 Supplement Table 3B is used to determine shearwall capacity. Assuming SPF framing with G=0.42, 8d nails, 15/32 Structural sheathing, and nailing of 6 /12 and 4 /12 along the panel edges. 98

98 Traditional (Segmented) Shearwall Method 2884# 3360# Required Capacity = 2884lbs/8ft = 361 plf 15/32" WSP (8d at 6/12) SPF Framing (G = 0.42) Tabulated Capacity = 230(1.4) = 422 plf Shearwall Capacity = 422 plf * 8 ft = 3376 lbs Holddown Capacity = 422 plf * 8 ft = 3376 lbs Required Capacity = (2884lbs lbs)/16ft = 390 plf 6752 lbs 3376 lbs Base Shear = 6244 lbs 6752 lbs 15/32" WSP (8d at 6/12) SPF Framing (G = 0.42) Tabulated Capacity = 230(1.4) = 422 plf Shearwall Capacity = 422 plf * 16 ft = 6752 lbs Holddown Capacity = 422 plf * 8 ft = 3376 lbs summing dissimilar materials With increased shear capacities (40% increase) and summation of dissimilar materials (100 plf for gypsum) the required sheathing has been reduced, however there are still numerous interior holddowns required. 99

99 Perforated Shearwall Method 2884# 3360# 8152 lbs 8152 lbs Base Shear = 6244 lbs Required Capacity = 2884lbs/23.5 ft = 123 plf Percent FH Sheathing = 23.5'/36' = 65% Shear Capacity Adjustment (H/2) = /32" WSP (8d at 6/12) SPF Framing (G = 0.42) Tabulated Capacity = (230(1.4) + 100) * 0.85 = 359 plf Shearwall Capacity = 359 plf * 23.5 ft = 8430 lbs Holddown Capacity = 422 plf * 8 ft = 3376 lbs Required Capacity = (2884lbs lbs)/21ft = 297 plf Percent FH Sheathing = 21'/36' = 58% Shear Capacity Adjustment (5H/6) = /32" WSP (8d at 4/12) SPF Framing (G = 0.42) Tabulated Capacity = (355(1.4) + 100) * 0.62 = 370 plf Shearwall Capacity = 370 plf * 21 ft = 7770 lbs Holddown Capacity = 597 plf * 8 ft = 4776 lbs perforated shearwall capacity By using the perforated shearwall method the amount of sheathing has been increased, however holddowns are only required at each end of the shearwall. The WFCM uses 60% of the dead load to resist wind uplift. In most cases, the wind uplift is much greater than 60% of the dead load, and will require more than the dead load alone to offset the wind force component. For seismic loads, the holddowns are conservatively sized in the WFCM to meet the shear capacity of the shearwall. 100

100 Copyright 2001 American Forest & Paper Association, Inc. 221 Perforated Shearwall Method 8' Wall 10' Wall Percent Full-Height Sheathing 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Maximum Unrestrained Opening Height (Window or Door Height) 2'-8" 4'-0" 5'-4" 6'-8" 8'-0" 3'-4" 5'-0" 6'-8" 8'-4" 10'-0" Effective Shear Capacity Factor IBC Using the perforated shearwall method, shear capacity is reduced using effective shear capacity factors. Assuming an 8 wall height, window openings are H/2 or 4 and door openings are 5H/6 or 6-8. Interpolation is permitted based on percent full-height sheathing in the wall. 101

101 Shearwall Design Methodologies Safety Factor Adjustments Summing Dissimilar Materials Perforated Shearwall Method System Factors for Stud Walls 102

102 System Factors for Stud Walls Issues: Repetitive member factor, C r sheathed with minimum materials studs act alone C r underestimates system effects Solution: Develop factors based on structural design procedures which account for system effects The fourth design methodology was the incorporation of system factors for stud walls. Problems with current practice were: assumptions that walls were sheathed with minimum materials, that studs act alone as bare members, and the current repetitive member factor, C r, underestimates system effects. 103

103 System Factors for Stud Walls Components in the System Effect Partial Composite Action Interaction between structural elements providing increased stiffness and strength Load Sharing A characteristic of repetitive member assemblies where load is distributed according to relative member stiffness Structural Redundancy The reserve strength available in an assembly after failure of an individual member Textbook methods tend to over-predict composite action for wood assemblies because they assume full composite action. Wood assemblies demonstrate partial composite action due to nail slip. In general load sharing can be simply explained that the stiffer member will carry more load. If you had an infinitely stiff load sharing element, all joists would share load equally. Since this is not the case, the stiffer member picks up load first until it reaches its capacity and then "shares" that load with adjacent members. 104

104 System Factors for Stud Walls Bending design values, F b, for wood studs shall be permitted to be multiplied by the following factors in lieu of the 1.15 repetitive member factor 2x4 2x6 2x8 2x10 2x IBC The system factors are used in lieu of the 1.15 repetitive member factor, C r. Note that a value of 1.15 is retained for 2x12 s. 105

105 System Factors for Stud Walls Requirements for system factors for wall studs (IBC ): Resisting wind loads Exterior min 3/8" wood structural sheathing min 8d common nails max 6" o.c. edges and 12" o.c. field Interior min 1/2" gypsum wallboard sheathing min 5d cooler nails max 7" o.c. edges and 10" o.c. field W Example: Gable end walls L Gable endwalls are good example of type of wood system where use of new system factors for stud walls is applicable. 106

106 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Snow Shear walls Standard Wall Wind Seismic Design Examples Now with this background on shearwalls, let s look at load resistance behavior with WFCM provisions for each of wind and seismic loads. 107

107 Wind Issues Let s first look at wind issues. 108

108 High Winds & Consequences More damage is caused annually by wind in the United States than by fire. Wind damage is caused by: Hurricanes, Tropical Storms, Tornadoes, and Intense Thunderstorms. More damage is caused annually by wind in the United States than by fire. Wind damage is caused by: Hurricanes, Tropical Storms, Tornadoes, and Intense Thunderstorms. 109

109 Consequences This is an example of the consequences of poor design and construction. 110

110 High Winds & Consequences Each hurricane has a personality Some destroy though wind Some primarily through flooding No matter the personality of a storm, damage does not have to be significant! The application of sound engineering and diligence in construction will reduce losses dramatically! Each hurricane has a personality Some destroy though wind Some primarily through flooding No matter the personality of a storm, damage does not have to be significant! 111

111 Consequences F-3 Tornado OK! This is an example of damage in Central Florida resulting from an F-3 tornado. Neighboring buildings designed and constructed in accordance with the Florida Building Code suffered very little damage. 112

112 Consequences There is little evidence that the building material system matters. Concrete masonry, wood-frame, and steelframe buildings all suffer catastrophic damage. But, properly designed and constructed buildings of each material system fare quite well. Concrete-masonry construction, light-gauge steel construction and wood-frame construction are all good if properly designed and constructed. There is little evidence that the building material system matters in resisting damage. Concrete masonry, wood-frame, and steel-frame buildings suffer catastrophic damage. But, properly designed and constructed buildings of each material system fare quite well. 113

113 Frequently Observed Damage Damage common to many buildings: Loss of roof shingles and other roofing membranes resulting in water damage Loss of roof sheathing, especially at gable ends and along edge zones Loss of roof rafter systems Loss of windows and doors - resulting in pressurization of building Damage common to many buildings: Loss of roof shingles and other roofing membranes resulting in water damage Loss of roof sheathing, especially at gable ends and along edge zones Loss of roof rafter systems Loss of windows and doors - resulting in pressurization of building 114

114 Dispelled Myths Continuing pattern of damage dispels several myths: Concrete-masonry and steel construction are superior to wood-frame construction in high wind regions. Wood-frame construction cannot withstand hurricane wind loads. Wind resistive construction is cost prohibitive. Continuing pattern of damage dispels several myths: Concrete-masonry and steel construction are superior to wood-frame construction in high wind regions. Wood-frame construction cannot withstand hurricane wind loads. Wind resistive construction is cost prohibitive. 115

115 Dispelled Myths Concretemasonry construction is superior? This type of damage should not have occurred! This type of damage dispelled the myth of the superiority of concrete-masonry construction. 116

116 Common Causes of Damage Masonry Buildings: Inadequate vertical and horizontal reinforcing Improper placement of bars in load bearing elements Inadequate coverage of bars by concrete grout Inadequate bond of mortar to masonry units Lack of mortar - end joints, bed joints Dehydration of mortar Masonry Buildings: Inadequate vertical and horizontal reinforcing Improper placement of bars in load bearing elements Inadequate coverage of bars by concrete grout Inadequate bond of mortar to masonry units Lack of mortar - end joints, bed joints Dehydration of mortar 117

117 Dispelled Myths Bad bond from dehydrated mortar on block lay-up This photo illustrates the problem with dehydrated mortar. The mortar stuck to the top of the block, but not to the block laid on top of it. This masonry was probably laid up on a hot Florida day. The block was probably very hot and dry and once the mortar bed was laid, the free moisture was sucked out preventing a good bond. Also, it is obvious that this wall had inadequate vertical reinforcing. 118

118 Dispelled Myths Inadequate reinforcing of masonry units This photo illustrates inadequate reinforcing of masonry units. 119

119 Dispelled Myths Inadequate consolidation of grout in reinforced cells Inadequate consolidation of the grout in the reinforced cells is also an all too common problem. Note the gap! Much of the reinforcing steel did not show evidence of a grout bond. This kind of problem can be easily prevented. 120

120 Common Causes of Damage Wood-frame Buildings: Inadequate nailing of built-up corners Inadequate nailing of wall sheathing Inadequate nailing of roof sheathing Inadequate fastening of roof to walls Inadequate fastening to foundation Lack of shear diaphragms to transfer loads Connections! What kind of problems do wood-frame buildings all too frequently have? Wood-frame Buildings: Inadequate nailing of built-up corners Inadequate nailing of wall sheathing Inadequate nailing of roof sheathing Inadequate fastening of roof to walls Inadequate fastening to foundation Lack of shear diaphragms to transfer loads 121

121 Hurricane Andrew 1992 Here are some examples of unnecessary damage caused by Hurricane Andrew in Similar damage was observed in Hurricane Hugo in 1988 and the hurricanes that struck Florida in

122 Hurricanes East Florida 2004 This damage occurred along the East coast of Florida in

123 Common Causes of Damage Steel-frame Buildings: Inadequate stud gauge (strength) Inadequate construction & fastening of corners Inadequate fastening of wall sheathing Inadequate fastening for roof sheathing Inadequate fastening of roof to walls Inadequate fastening to foundation Lack of shear diaphragms to transfer loads What about steel-frame buildings? Their problems are very similar to that of wood-frame: Inadequate stud gauge (strength) Inadequate construction & fastening of corners Inadequate fastening of wall sheathing Inadequate fastening for roof sheathing Inadequate fastening of roof to walls Inadequate fastening to foundation Lack of shear diaphragms to transfer loads 124

124 Hurricane Charley West Florida 2004 This is a photograph of a commercial building along Florida s Gulf Coast in 2004 following the passage of Hurricane Charley. 125

125 Hurricane Charley West Florida 2004 This is another picture from Hurricane Charley. Yet, the same type of damage was observed following the other three hurricanes that struck Florida in

126 Damage is Preventable Most damage is preventable through proper design and construction! Proper design and construction requires: Basic understanding of wind loads; Basic understanding of wind-resistive construction; Commitment to properly design and construct by each of the players in the construction process! Most damage is preventable through proper design and construction! Proper design and construction requires: Basic understanding of wind loads; Basic understanding of wind-resistive construction; Commitment to properly design and construct by each of the players in the construction process! 127

127 Hurricane Charley Eye northern tip Pine Island Florida 2004 This photo illustrates this point. This house on the Northern tip of Pine Island is virtually unscathed, yet the eye of Hurricane Charley went right through this area. 128

128 Hurricane Charley Eye northern tip Pine Island Florida 2004 This is another house that is virtually unscathed following Hurricane Charley. 129

129 Hurricane Charley Eye northern tip Pine Island Florida 2004 And, yet another example. This is one of several wood-frame apartment buildings that suffered very little, if any, damage. 130

130 Wind Design Proper design of wood structures to resist high wind loads requires the correct use of wind load provisions and member design properties. A thorough understanding of the interaction between wind loads and material properties is important in the design process. 131

131 Wind Basics LIFT WIND PRESSURE or SUCTION Reactions UPLIFT OVERTURNING SLIDING SHEAR Wind-structure interaction is highly complex. Wind can induce a variety of structural responses as a whole building, and on individual components and assemblies, as seen here. Each of these responses needs to be checked for structural integrity as part of the wind design process. 132

132 Building Code Requirements Generally, building codes require: Buildings to be designed for the 50-year wind event - that is - a 2% probability that design winds will be met or exceeded in any one year. For hurricane prone regions, the probability is based on a Class III storm. Wind speeds are measured at 33 ft. (10 meters) above ground for open terrain. Generally, building codes require buildings to be designed for the 50-year wind event - that is - a 2% probability that design winds will be met or exceeded in any one year. For hurricane prone regions, the probability is based on a Class III storm. Wind speeds are measured at 33 ft. (10 meters) above ground for open terrain. 133

133 Wind Design For 1- and 2-family dwellings, wind resistive design is usually based on: Simplified or analytical procedures of ASCE 7-98, or Low rise wind load provisions of the IBC (2000 IBC and 1997 NDS) or ANSI/AF&PA 2001 WFCM engineered and prescriptive. The NDS provides factors to adjust design values for wood members and connections for specific conditions frequently encountered in service. It does not set forth general requirements for adjusting design values for all possible applications and related conditions of use, particularly those involving extreme loading and service exposures (see 1991 Commentary for example). To include all conditions in this manner would require use of overly conservative and economically prohibitive adjustment factors not required for most applications. However, it is the designer's responsibility to determine the design value adjustment factors that are appropriate for each application. 134

134 Wind Design Analysis of low rise wood frame buildings review wind load provisions in accordance with the IBC reference: 2000 IBC and ASCE 7-98 design examples for designing a low rise wood structure to resist IBC wind loads reference: AF&PA 2001 WFCM The NDS provides factors to adjust design values for wood members and connections for specific conditions frequently encountered in service. It does not set forth general requirements for adjusting design values for all possible applications and related conditions of use, particularly those involving extreme loading and service exposures (see 1991 Commentary for example). To include all conditions in this manner would require use of overly conservative and economically prohibitive adjustment factors not required for most applications. However, it is the designer's responsibility to determine the design value adjustment factors that are appropriate for each application. 135

135 ASCE 7-98 Wind based on 3 Second Gust measurement. hurricane wind speed contours based on 500- year recurrence on Atlantic/Gulf coast. hurricane wind speeds adjusted from 500-year to 50-year recurrence for use with ASD. divide 500 year values by 1.6 to get 50 year value Hurricane Importance Factor built into map. There are varying wind load provisions in local, state and model building codes currently used in the United States. Most of these provisions are based on wind engineering research conducted over the last 50 years. Proposals to change current code provisions are the result of interpretations of new state-of-the-art wind engineering research. The wind load provisions of the national load standard ASCE 7-98 Minimum Design Loads for Buildings and Other Structures include general wind load provisions which, in turn, are used as the basis for wind load requirements in most U.S. building codes. For the purposes of this paper, the references to wind loads in this article have been limited to the provisions found in ASCE Wind Load Provisions Design wind load provisions in ASCE 7-98 are based on wind speed data collected during severe wind events in the United States. The wind speed contours provided in ASCE 7-98 are presented in terms of three second gust. Three second gust wind speed is based on the peak wind speed at a given height and exposure averaged over 3 seconds. The three second gust wind speed data has been statistically adjusted to a 50-year recurrence interval with an average annual probability of occurrence of 2 percent. The data has also been adjusted to a reference height of 33 feet and Exposure Category B, which assumes a flat, open terrain with scattered obstructions. The wind load provisions of ASCE 7-98 provide adjustments for variations from reference conditions such as increased wind speeds during hurricane events, different exposure conditions, different elevations, and localized peak gusts. 136

136 Design Gust Wind Speeds (mph) ASCE 7-98 / IBC 3-second Gust Wind Speeds Batts, M. E., Cordes, M. R., Russell, L. R., Shaver, J. R. and Simiu, E. (1980). Hurricane Wind Speeds in the United States, National Bureau of Standards, Report Number BSS-124, U.S. Department of Commerce. Durst, C. S. (1960) Wind Speeds over Short Periods of Time, Metorological Magazine, Vol. 89, pp ESDU (1983). Strong Winds in the Atmospheric Boundary Layer, Part 2: Discrete Gust Speeds, Engineering Sciences Data Unit Item No , London, England. Georgiou, P. N., Davenport, A. G. and Vickery, B. J. (1983). Design Wind Speeds in Regions Dominated by Tropical Cyclones, 6 th International Conference on Wind Engineering, Gold Coast, Australia, March and Auckland, New Zealand, 6-7 April. Georgiou, P. N. (1985). Design Windspeeds in Tropical Cyclone-Prone Regions, Ph.D. Thesis, Faculty of Engineering Science, University of Western Ontario, London, Ontario, Canada. Krayer, W. R., and Marshall, R. D. (1992). Gust Factors Applied to Hurricane Winds, Bulletin of the American Meteorological Society, Vol. 73, No. 5, pp Vickery, P.J., and Twisdale, L. A. (1995a). Wind-Field and Filling Models for Hurricane Wind-Speed Predictions, Journal of Structural Engineering, Vol. 121, No. 11, pp Vickery, P.J., and Twisdale, L. A. (1995b). Prediction of Hurricane Wind Speeds in The United States, Journal of Structural Engineering, Vol. 121, No. 11, pp Vickery, P.J., and Skerlj, P. F. (1999). Hurricane Gust Factors Re-Visited, Submitted to Journal of Structural Engineering Vickery, P.J., Skerlj, P. F. and Twisdale, L. A.. (1999). Simulation of Hurricane in the United States Using an Empirical Storm Track Modeling Technique, Accepted for publication in Journal of Structural Engineering 137

137 ASCE 7-98 Overview of Wind Loads Three design method options Method 1 - Simplified Procedure Method 2 - Analytical Procedure Method 3 Wind Tunnel Procedure WFCM Ch 3 Prescriptive WFCM Ch 2 Engineered ASCE 7 contains three methods for determining wind loads for design. Prescriptive design requirements in the 2001 WFCM make use of the Simplified Procedure. However, engineered design typically uses Method 2, the Analytical Procedure. 138

138 Wind Speeds Historically, wind speed data was in fastestmile wind speeds 1-minute mean. Inherent flaw due to variable averaging time Beginning in the 1970 s the collection of fastest-mile data was phased out in favor of 3-second peak gust data. Constant averaging time of 3-seconds Historically, wind speed data was in fastest-mile wind speeds 1-minute mean. This is an inherent flaw due to variable averaging time. Beginning in the 1970 s the collection of fastest-mile data was phased out in favor of 3- second peak gust data which is a constant averaging of wind speed over a time interval of 3- seconds. 139

139 Wind Speeds Vary with Time This printout of a anemometer shows the variance that occurs in a wind event. 140

140 Wind Speeds Different wind speed methodologies based on different duration of measurements. Fastest-mile wind speeds include gust factors. New codes include conversion tables for determining equivalencies V-3s V-fm The different wind speed methodologies that have been used in the building codes over the years are based on different duration of measurements. Current code provisions are based on 3-second gust wind speeds. Fastest-mile wind speeds included gust factors. Codes commonly include conversion tables for determining equivalencies of the two methods as a means by which to continue the use of various prescriptive design and construction standards. 141

141 ASCE 7-98 Exposures A Center of large cities (not for Simplified Method) B Suburban, use as DEFAULT >60% to 80% of all buildings are in this category C Open country, 1500 ft transition zone D Over water, EXCEPT on hurricane coast due to surface roughness of the water surface Here are the exposure categories as identified in ASCE Suburban exposure B is the DEFAULT. Other categories are used where special condition warrant. WFCM 2001 tables are based on exposure B. However, tables are provided for exposure C in an Appendix. 142

142 ASCE 7-98 Exposures Exposure A Exposure B Urban Exposure C (<1500 of B) Exposure D Exposure A is rare and should be used with extreme caution. Consideration is being given to elimination of this category completely. Exposure B is the default for the WFCM 2001, and an appendix provides tables for Exposure C conditions. 143

143 ASCE 7-98 Exposures Exposure A Large city center with at least 50% of the buildings having a height in excess of 70 ft. The subject building must have this terrain upwind for at least 1/2 mile or 10 times the height of the building, whichever is greater. Exposure A is rare and should be used with extreme caution. Consideration is being given to elimination of this category completely. 144

144 Exposure B Urban Exposure B Urban Urban area with numerous closely spaced obstructions having the size of single family dwellings or larger. For all structures shown Exposure B extends more than 1500 ft. or 10 times the height of the structure, whichever is greater, in any wind direction. 145

145 Exposure B Suburban Suburban residential area with mostly single family dwellings. Structures in the center of photograph have an Exposure B terrain greater than 1500 ft. or 10 times the height of the structure, whichever is greater, in any wind direction. Exposure B Suburban 146

146 Exposure B Urban w/ Hole Exposure B with a Hole Structures in the foreground are subjected to an Exposure B terrain. Structures in the center top adjacent to the clearing on the left, which is greater than 1500 ft. in length, are subjected to an Exposure C when wind comes from the left over the clearing. 147

147 Exposure C Exposure C (<1500 of B) Open terrain with scattered obstructions having heights generally less than 30 ft. For most wind directions, all structures in the photo are less than 1500 ft. or 10 times the height of the structure from an open field, preventing the use of Exposure B. 148

148 Exposure C Classic Flat open grassland with scattered obstructions having heights generally less than 30 ft. Exposure C 149

149 Exposure D A building at the shoreline (excluding shorelines in hurricane prone regions) with wind flowing over open water for a distance of at least one mile. Included in Exposure D are inland waterways, lakes and coastal areas in CA, OR, WA, AK. Exposure D 150

150 WFCM 2001 Provisions - Wind per 2000 IBC provisions mph wind speed (3 second gust) Exposure B & C Exceptions: Main Wind Force Resisting System (MWFRS) not checked for 10 psf minimum load on building vertical projected area (under review by ASCE 7) shearwall and diaphragm designs shall not be less than tabulated requirements for 100 mph wind speeds Wind provisions for the 2001 WFCM are per IBC 2000 provisions: mph based on 3 second gust. Note that in the WFCM 2001, the main wind force resisting system (MWFRS) in not checked for a 10 psf minimum load on a building vertical projected area as required by IBC This is currently under review by ASCE 7 Committee with the expectation that the 10 psf requirement will drop to a much lower magnitude. Further, shearwall and diaphragm designs must resist 100 mph wind speeds according to the WFCM

151 Wind Load Resolution Load Path Remember this? This is a graphical illustration of how wind load moves through various building assemblies and gets transferred into the ground. Note the important components: the windward wall, the roof diaphragm, and the side shear walls with associated shear and hold-down anchorage devices. 152

152 WFCM 2001 Provisions - Wind Components and Cladding (C&C) Main Wind Force Resisting Systems (MWFRS) Found in: lateral provision tables in Chapters 2 (engineered) and 3 (prescriptive) There are two systems that are considered in wind design: components and cladding (C&C), and Main Wind Force Resisting System (MWFRS), with correspondingly different design approaches. Applicable provisions for each are found in both prescriptive and engineering provisions of the WFCM. 153

153 WFCM 2001 Provisions - Wind components and cladding Table 2.4 Example: roof and wall sheathing (out of plane) Under C&C design, Table 2.4 governs for components such as roof and wall sheathing subjected to out-of-plane wind loading. 154

154 WFCM 2001 Provisions - Wind Main Wind Force Resisting systems Table 2.5 a, b Example: studs, beams, sheathing (primary structural skeleton) However, MFWRS provisions are manifested in Tables 2.5 A and B for much larger primary structural skeleton assemblies such as roof or floor diaphragms. 155

155 WFCM 2001 Provisions - Wind Roof and Wall Sheathing / Cladding for Panels are found in Chapter 3 Tables 3.12A, 3.13A & B For panels, wall sheathing and cladding data is found in Chapter

156 WFCM 2001 Provisions - Wind From 1.3 Definitions: Cladding Exterior structural elements that receive loads normal to their surface. (i.e. exterior finish materials) Sheathing The structural covering used directly over framing members such as studs, joists, or rafters, which transfers perpendicular loads to the framing material. The difference between cladding and wall sheathing is subtle here are the WFCM 2001 definitions. 157

157 WFCM & Wind Behavior LIFT WIND PRESSURE or SUCTION Reactions UPLIFT OVERTURNING SLIDING SHEAR The Wood Frame Construction Manual takes these wind basics fully into consideration to provide an engineered design of wood-frame buildings for wind speeds up to 150 mph. 158

158 Concrete-masonry residence Hurricane Charley Burnt Shore Road, south of Punta Gorda, FL Properly designed and constructed This is a concrete-masonry building under construction along Burnt Store Road south of Punta Gorda where Hurricane Charley caused extensive damage. Except for severely twisted interior steel studs and the loss of dry-in felt, no damage occurred. This building is properly designed and constructed. 159

159 Wood frame residence Hurricane Charley Bokeelia, FL Properly designed and constructed using WFCM This wood-frame building in Bokeelia under construction only suffered loss of building paper and dry-in felt. This building complies with the design provisions of our Wood Frame Construction Manual. 160

160 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Snow Shear walls Standard Wall Wind Seismic Design Examples Now let s discuss load resistance behavior with WFCM provisions for seismic loads. 161

161 Seismic Issues Properly designed buildings can also withstand most seismic forces. Seismic loads arise from ground shaking which can be a result of many causes. Earthquakes by far are the most serious and unpredictable seismic load type. Other more predictable seismic loads arise from human-induced activities. 162

162 Seismic Loads ground shaking: earthquake railway tracks/trains heavy machinery manufacturing (punch presses) foot steps Seismic loads arise from ground shaking which can be a result of many causes. Earthquakes by far are the most serious and unpredictable seismic load type. Other more predictable seismic loads arise from human-induced activities. 163

163 Seismic Loads time-varying ground motion distance time f(x,t) how does this translate to a load? The primary feature of seismic motion is that its magnitude varies with time. The time variation can be very short, such as a sharp jolt, or longer, such as a slow rumble. Moreover, the motion direction is typically random and constantly changing. Such a behavior can be described in terms of a wave. Using recorded seismic data, we can describe a seismic motion mathematically in terms of a wave function of distance and time. 164

164 Wave Characteristics amplitude frequency / period duration acceleration amplitude time Period (1 cycle) Waves have three primary characteristics: amplitude (the magnitude of the wave), frequency (the number of complete wave cycles per second) or inversely its period (the number of seconds per complete wave cycle), and duration (the time lapse of the wave). 165

165 Wave Characteristics damping (wave decay) acceleration damping ratio (%) time Damping describes the decay rate of the wave amplitude as the wave dies out. Friction in the wave generating system is an example that causes waves to damp. 166

166 Building Characteristics mass stiffness damping natural frequency of vibration displacement x mass stiffness time damping 2 x x m + c + kx 2 t t With respect to dynamic response, buildings offer three primary characteristics: mass of the building or sub-assemblies, stiffness of the building structural system, and damping inherent in the building construction. These can be simply modeled as the lollypop shown here. If the stick of the lollypop is sufficiently thin (low stiffness), and the mass is pulled back and released, the mass will swing back and forth in free motion. The free sway motion can be described by the mass displacement wave shown here, with measurable frequency. This simple sway mode is known as the natural frequency of vibration. Mathematically, the sway motion equation takes the form of a second order differential equation with respect to time. 167

167 Building Response Equation of motion response m &&+ x cx& + kx = demand f ( x, t) mass inertia system damping system stiffness disturbance In the motion equation, all the components of the dynamic structural behavior are evident. The equation here is written in terms of linear displacement, x, although angular displacement terms (not shown) and other directional displacements may be present. Solution techniques for this equation exist mathematically. 168

168 Building Response Motion Modes fundamental / natural / 1st mode 2nd mode 3rd mode etc Solution of the motion equation can lead to a modal result: a series of frequencies at which the structure will freely vibrate if disturbed. An example of this solution can be heard when a guitarist uses fret harmonics (octave pitches) to tune a guitar. In a building, the sway shape takes different forms that correspond to the modal frequencies in the solution. Thus, a structure can have a number of sway modes with associated frequencies of vibration. 169

169 Force Demand (Load) inertial force = mass x acceleration F = m a = m ẋ. x mass stiffness damping acceleration a = ẋ. Let s put the whole seismic problem together now. Ground shaking occurs with a certain acceleration, a, moving the soil under the building. As the soil moves, the building mass wants to stay put due to its inertia, putting a force on the structure equal to the mass times the exciting acceleration. Eventually the mass moves, lagging the exciting acceleration, causing further inertial forces to develop on the structure. This gets even more problematic when the exciting acceleration changes direction, as the mass wants to keep moving (through inertia) in the the original direction of mass movement. This is sometimes referred to as the whipping force. 170

170 Resonance seismic frequency = building frequency DESTRUCTION = If the exciting wave characteristics match any of the building s modal wave characteristics, then resonance results when the exciting and response systems vibrate in unison. Resonance is very dangerous since the response system normally self-destructs due to its inability to cope materially with the exciting wave. Hence, it is very desirable from a building design perspective to separate building modal response frequencies from any potential exciting frequencies. 171

171 Building Response Motions planar sway (racking) torsional twist center of stiffness racking twist Buildings move under dynamic conditions. Two principle movements are: racking and twist. We ll talk more on twist in a minute. 172

172 Resisting Elements - Diaphragms horizontal force transfer in-plane shear V max at edges Structures have horizontal surfaces that can be used to transfer loads applied laterally to the structure. These surfaces, transferring in-plane loads are commonly called diaphragms, and can be characterized as a wide, flat deep beam. An inertial mass load can originate in the surface/diaphragm and transfer the same way. Resulting shear forces develop across the surface, with maximum values occurring at the supported edges of the surface. These maximum reaction forces are the lateral forces that are transferred into the vertical building elements below, causing them to rack.. 173

173 Resisting Elements - Shearwalls racking resistance perimeter nailing sliding resistance These lateral racking forces applied at the top of the wall can be picked up by shearwalls. In a wood shearwall, the panel perimeter nails provide the bulk of the racking resistance through wood bearing and nail deformation when the lateral external force is applied. Horizontal wall sliding is resisted by nailing or other anchorage installed along the bottom of the shearwall sufficient to resist the external lateral force. 174

174 Resisting Elements - Shearwalls panel aspect ratio racking action cantilever beam action In order to make this concept work, panels must have a height-to-width aspect ratio of less than 3.5 to 1. This ratio is sufficient to develop racking action in the shearwall panel. Aspect ratio s greater than this produce cantilever beam action - a completely different behavior that is much less effective in resisting lateral forces, as mentioned previously. 175

175 Resisting Elements - Hold Downs overturning Finally, overturning may be a problem, especially for high aspect ratios. These skinny panels usually develop high overturning forces at the bottom corners of the walls that need to be resisted with the installation of special hold-down hardware. 176

176 Resisting Elements - Diaphragms twist mass center stiffness center mass center stiffness center eccentricity Building forms impact how lateral forces get transferred into the vertical supporting elements. Here s an example. A floor has a center of mass located somewhere in it. The structural system below provides a torsional stiffness that can also be centered somewhere within the floor plane. If the stiffness and mass centers coincide, then the building will simply rack in the direction of the applied lateral load. If however, the mass and stiffness centers are displaced, the building frame will twist. The greater the displacement, the greater the twist. The diaphragm reactions transferred to the top of the shearwalls can also become very large. Thus, good design for lateral performance would suggest that centers of mass and stiffness be kept in as close proximity to each other as possible. This subject is important for a rigid analysis where the stiffnesses of the system components are known. The WFCM 2001 assumes a flexible analysis: flexible components that lend to a tributary area approach for the loads. 177

177 Building Response The theory of light and strong... There is another way to resist lateral forces - a technique that dates back to early human inhabitation some 10,000 years ago. Archaeological findings prove the theory of light and strong in known seismically active areas of the earth. The theory holds that humans discovered early that heavy things fall down easily when disturbed with catastrophic results. Light things are not disturbed nearly as easily, and are much easier to support and be made strong. Thus, the simple tent has become a common domestic structure to many peoples of the earth in regions that are seismically active, even to this day. Wood frame structures tend to fit this philosophy, mainly because of wood s very high strength-to-weight ratio. 178

178 Load Provisions - ASCE 7-98 The seismic problem statement: seismic event site conditions building type and use ASCE 7-98 provides the data and methodology to determine loads for buildings - seismic loads in this case. The parameters to do this include: data on the design seismicity, site sub-surface conditions, and building type and intended use. 179

179 Load Provisions seismic maps & ground accelerations examine for short periods S s and 1 second period S 1 ASCE 7-98 provides seismic maps of the US contoured in terms of %g (% gravity at 32.3 ft/s 2 ) ground acceleration. Two such maps provide for short period seismicity, and 1 second period seismicity, respectively. Both will be needed to determine which governs later on. 180

180 Load Provisions site conditions Sub-terrainean site conditions are presented in terms of a site class letter. Characteristics of each site class are given in terms of soil bearing capacity, penetration number, or sonic velocity criteria - basically to assess underlying soil density. 181

181 Load Provisions site conditions coefficients F a and F v The acceleration-based site coefficient (at 0.3s period), F a, and velocity-based site coefficient (at 1.0s period) are determined from these ASCE 7-98 tables. 182

182 Load Provisions building type and use These ASCE 7-98 tables arrive at the determination of the building class for seismic design purposes. The building class sets out which method is to be used for determining the respective loading. 183

183 Load Provisions seismic design category S 2 3 DS = Fa S S s D 1 = Fv S1 2 3 The design 5% damped spectral response acceleration at short periods, and the corresponding one for 1 second periods is determined from these formulae, using site accelerations and site conditions coefficients as input. Using the spectral acceleration numbers with the seismic use group for the building in the tables, yields the seismic design category for our structure, on our site. The seismic design category is important as it is used widely in the AF&PA 2001 Wood Frame Construction Manual. 184

184 Load Provisions seismic design category or you can go to the USGS website and use their calculator to find a seismic design category for any building by longitude/latitude or by zip code. 185

185 WFCM 2001 Provisions - Seismic per 2000 IBC provisions seismic design categories A - D WFCM considers seismic loads for design categories A to D. 186

186 WFCM 2001 Seismic Provisions Chapter 2 Engineered use with seismic design categories A to E Chapter 3 Prescriptive use with seismic design categories A to D The 2001 WFCM Engineering and Prescriptive provisions make use of the seismic design categories from ASCE Note that prescriptive provisions only apply up to category D, and engineered provisions up to category E. Categories above E are beyond the scope of the WFCM. 187

187 Load Provisions Story shears distribution (Equivalent Lateral Force) ASCE 7-98 roof W RD F RD V wall1 floor1 W FD1 F FD1 V wall2 floor2 W TOT building masses V base shear story forces story shears WFCM Chapter 2 Engineering provisions are based on the ASCE 7-98 Equivalent Lateral Force procedure. Building masses/weights are calculated and collected at floor plane levels. The seismic event base shear is calculated from the seismic loads and distributed on the basis of weights at each story as story forces. Finally, story shears are determined for each floor by adding all the story forces above the floor of interest. The story shears are the forces applied to the top of the lateral force resisting system at each floor level. 188

188 WFCM 2001 Provisions - Seismic Engineered seismic provisions includes: vertical distribution of shear, consistent with 2000 IBC requirements WFCM engineering provisions include vertical distribution of shear that is consistent with IBC 2000 requirements. 189

189 WFCM 2001 Provisions - Seismic Prescriptive seismic provisions based on IBC Simplified Design Method seismic loads are increased by factor of 1.2 vertical distribution of shear, redundancy, etc. included through 1.2 factor The prescriptive provisions are based on the IBC Simplified Design Method. Seismic loads are increased by a factor of 1.2 to include the effects of vertical shear distribution, redundancy, etc. 190

190 WFCM Provisions - Seismic Here s how the 2001 WFCM does this in detail: Chapter 2 Engineered Chapter 3 Prescriptive Let s take a look at how the WFCM provisions for seismic are presented, both for engineered and prescriptive design processes. 191

191 WFCM Chapter 2 Engineered obtain acceleration data from maps, enter this chart extract C s Chapter 2 facilitates the determination of story shears. First, enter Table 2.5C at the bottom with the seismic design category, and the spectral response accelerations S DS and S D1. Extract the pertinent value of the seismic response coefficient, C S. Consider the notes in the bottom of the table if they apply. 192

192 WFCM Chapter 2 Engineered extract weights and adjustments for vertical distribution of forces for walls and horizontal assemblies On the same table in the cells above, calculate heights h i and weights W i at each level using the formulae provided, and the vertical distribution factor C v for each level. 193

193 WFCM Chapter 2 Engineered determine total shear capacity required at each level for direction 1 Table ASCE 7-98 instructs the designer to consider seismic forces from two orthogonal directions. Table helps the designer determine the story shears for loads applied perpendicular to the ridge from the data just previously calculated from Table 2.5c. 194

194 WFCM Chapter 2 Engineered determine total shear capacity required at each level for the orthogonal direction 2 Table Table calculates the story shears in the other direction parallel to the ridge. Observe the notes in the bottom of each table. Proceed now to select assemblies to meet these load demands. 195

195 WFCM Chapter 3 Prescriptive applies to Chapter 3 buildings only table comes up with minimum length of sheathing required for a given wall for seismic load based on ASCE/IBC Simplified Design Procedure This Chapter 3 table applies to Chapter 3 buildings and gives the minimum length of sheathing required for a given wall for seismic load in a particular seismic design category. The C 2 is a geometry coefficient that accounts for non-square buildings. The seismic base shear is increased by 20% to account for vertical distribution of seismic forces, according to the ASCE/IBC Simplified Design Procedure. 196

196 WFCM Chapter 3 Prescriptive Prescriptive seismic provisions tables based on assumed structure dead load adjustments provided for roof, wall, and floor loads alternative to dead load assumptions WFCM tables are based on a presumed dead load, but if this varies, then adjustment equations are included to adapt the tabled values. The footnotes amend table data for masses other that those assumed in the Table. The roof and floor loads must be higher than 15 psf for dead load and the adjustment factors only increase this value. The wall loads begin at 15 psf and only go down in adjusted value. Knowing now the percent of full height sheathing, simply allocate the same amount to the shearwall lines in each direction of the building. 197

197 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Wind Snow Seismic Design Examples Snow Design Wind shearwall design Seismic shearwall design Let s look now at a few examples in depth for snow, wind and seismic design using the provisions of the 2001 WFCM. 198

198 Design Example 1 Snow Design Given: Geometry: 2x8 16 OC Materials: SPF #2 Loads: Dead 10 psf ceiling not attached to rafter Live 30 psf Performance: Δ LL L / 180 Find the maximum permissible span, L. Find the maximum permissible span for these 2x8 rafters on 16 OC. Loads and response criteria are given above. We ll resolve this design two ways: by direct calculation, and by using WFCM tables. 199

199 Design Example 1 Snow Design Solution (by calculation): Design Values NDS Supplement or 2001 WFCM Table 4A SPF #2 F b = 875 psi E = 1.4 million psi Adjustment Factors 2x8 Rafters C D = 1.15 (snow) C F = 1.2 C r = 1.15 A first step is to determine the design values for #2 SPF rafters. Using Table 4A of the Supplement chapter, the base values for F b and E are determined. Also referencing Table 4A, the adjustment factors for 2x8 rafters is determined. Table 4A of the Supplement chapter is the same as Table 4A of the NDS Supplement. 200

200 Design Example 1 Snow Design Solution (by calculation - ASCE 7-98): w total = w dead + w snow w snow = C s p f = (1.5)[(0.7) C e C t I p g ] where C s = roof slope factor = 1.5 p f = flat roof snow load C e = exposure factor = 1.0 C t = thermal factor = 1.1 I = importance factor = 1.0 p g = ground snow load Now determine the tributary load for a rafter due to the pressure loads. Here is the basic snow load equation from ASCE 7-98, that converts ground snow load to roof snow load. Note that this equation is used for balanced snow loads. Other unbalanced cases may need to be considered if drifting is an issue. 201

201 Design Example 1 Snow Design Solution (by calculation - ASCE 7-98): Loads: w dead = 10 psf (16in. / 12) = plf w snow = C s p f = (1.5)[(0.7) C e C t I p g ] = (1.5)(0.7)(1.0)(1.1)(1.0)(30 psf)(16 in. / 12) = 46.2 plf w total = = 59.5 plf Placing the numbers in the equation and adding in the dead load leaves us with 59.5 plf total load on a rafter. 202

202 Design Example 1 Snow Design Solution (by calculation): Strength: F b = F b C D C F C r where C D = load duration factor = 1.15 (NDS 2.3.2) C F = size factor = 1.2 (NDS Tables 4A & 4B) C r = repetitive member factor = 1.15 (NDS 4.3.9) F ' b w totall 8S 2 where S = section modulus = (NDS Table1B) L = length of span Check rafter strength first. Here are the basic equations we use to do this. The first equation calculates the design material stress in bending for the case we have at hand. The second equation is the capacity-demand relation in terms of material stress in bending. In the next slide, we ll re-arrange this equation to solve for the unknown length, L. Note that tables from the NDS Supplement are included in the Supplement chapter of the Wood Frame Construction Manual. Table 1B of the NDS Supplement presents Section properties of standard dressed (S4S) sawn lumber; while Table 4A of the NDS Supplement presents adjustment factors and base design values for bending design value, F b. 203

203 Design Example 1 Snow Design Solution (by calculation): Strength: calculate the moment-limited span: F b = F b C D C F C r = 875 psi (1.15)(1.2)(1.15) = 1,389 psi F 2 ' ' b b L = = = in. w totall 8S 8SF w total 8(13.14)(1389) (59.5 /12) = 14 ft. 4 in. Setting in the numbers, we adjust the wood bending stress for on-site conditions. Now, work the strength capacity-demand relation to isolate and solve for span, L. This is the maximum span limited by member strength. 204

204 Design Example 1 Snow Design Solution (by calculation): Stiffness: calculate the deflection-limited span: 4 Δ 5w livel LL 384EI 384EIΔ 5w 6 384( 1. 4x10 )( ) 5( 180)( 46. 2/ 12) LL L = 4 = 3 = live 194 in. = 16 ft. 3 in. Strength governs at 14 ft. 4 in. Now check stiffness. Again, isolate span L in the displacement relation. This answer is higher than the strength result, so the problem is strength-constrained: use the lower of the two values. Because these spans are long, and loading relatively light, shear should not constrain the design further. In almost all circumstances, lumber beam deflections are calculated using the conventional deflection formulas found in general engineering handbooks. For spans with uniformly distributed loads the deflection equation is δ = 5wL 4 /384EI, where w = uniformly distributed load in pounds per inch of span, L = span in inches, E = modulus of elasticity, I = moment of inertia in inches (Table 1B or bd 3 /12 for rectangular sections), and δ = deflection in inches. 205

205 Design Example 1 Snow Design Solution (by WFCM Table): L = 14 ft. 4 in. Here s another approach that you can use without a calculator or inverting equations. Go to WFCM 2001 Table 3.26c for Rafter Spans for 10 psf DL and 30 psf LL. Enter the table from the top with the cross-section size at 2x8 (green), and the left side of the table with the rafter spacing at 16 inches. After rafter spacing, select the appropriate species and grade: SPF #2. Read across the table row (yellow) intersecting the 2x8 column (green) and read a span of 14 ft. 4 in. 206

206 Design Example 1 Snow Design Solution (by WFCM Table 3.12B) - Panel: Any of these panel products will work since the actual rafter spacing is 16 OC Roof panel selection is most easily obtained from Table 3.12B for snow, and it is easily seen that with the loads in this example, any of the listed panel products will work since the actual rafter spacing is 16 inches OC. 207

207 Outline Purpose & Background Development process Code Acceptance Document layout Design provisions: Wind Snow Seismic Design Examples Snow Design Wind shearwall design Seismic shearwall design Let s continue with a final example on seismic and shearwall design using the provisions of the 2001 WFCM. First, a little background on seismic design methodology. 208

208 Design Example 2 - Prescriptive 2nd Level Wall of this home: Seismic SDC D1 Wind 120 mph Here s a design example right out of the WFCM Workbook - the second level wall of this house that is in Seismic Design Category D1 and a 120 mph wind load. We ll design the north (back) level 2 wall for seismic and wind respectively, then compare results. We ll consider both segmented and perforated shearwall variations in the solution. And we ll use the Chapter 3 Prescriptive provisions of the 2001 Wood Frame Construction Manual. 209

209 Design Example 2 - Level 2 Plan Walls on this floor are 9 ft tall Roof slope 12:12 so roof space is considered an additional story (front of Chapter 3) Here is the dimensioned second floor plan. 210

210 Design Example 2 - Level 1 Plan and the first floor plan. We ll be needing these dimensions. The second level wall is 9 feet tall. 211

211 Design Example 2 - Wall 40 9 Exterior Type I Shearwalls (segmented) (WFCM ) north elevation shaded areas show potential eligible shearwall panels Length of perpendicular wall 32 ft Perimeter edge nail spacing 6 Length of full height sheathing (L full height ) 28 ft The roof has a steep pitch - steep enough to warrant it being considered a story unto itself. The shaded areas shown on this level 2 north wall elevation represent the potentially available shearwall panels since their aspect ratios are less than 3.5 to 1. Their lengths along the bottom of the wall sum to 28 ft. 212

212 Design Example 2a - Seismic D1 Two stories braced (roof and level 2) Building Level 2 L min = 32 L max = 40 In seismic design, these overall level 2 floor dimensions are important. We assign the the biggest dimension to L max, and the smaller to L min. 213

213 Design Example 2a - Seismic D1 Two stories braced (roof and level 2) Table 3.17C C 1 = 57 C 2 = 15 Using Table 3.17C from the 2001 WFCM, we extract the coefficients C 1 and C 2. Do this by first locating the wall in the drawings in the left side of the table. Since the roof in our example is a story, we choose the diagram corresponding to Roof plus 1 story. The intersection of L max (left) and the seismic design class (top) yields C 1. C 2 is found at the bottom in the SDC column. 214

214 Design Example 2a - Seismic D1 L SheathingRequired = C1 + L MAX MIN LMIN C = = 19.4 ft < shearwall panels provided (28 ft) OK Using the extracted coefficient values from the table, perform the calculation of the formula at the top of the table to get the length of required full-height sheathing for a Type I segmented shearwall design. Our wall is sufficiently long, thanks to all the shearwall panels between the windows. 215

215 Design Example 2b - Wind 9 Exterior Type I Shearwalls (segmented) (WFCM ) north elevation shaded areas show potential eligible shearwall panels Length of perpendicular wall 32 ft Perimeter edge nail spacing 6 Length of full height sheathing (L full height ) 28 ft Wall height adjustment factor (C WH ) 9 /8 = Now let s consider the same segmented wall, but subject to the 120 mph wind load. The house is situated in Exposure B site conditions. Since our wall height is 9ft, we must adjust our solution from the standard 8 ft height by using the C WH factor. 216

216 Design Example 2b - Wind Building Level 2 W = 32 Two stories braced (roof and level 2) 120 mph Exposure B parallel to ridge L = 40 The wind table assigns the overall floor dimensions to different variables: L for the length of the wall of interest, and W to the width of the building perpendicular to it. Our wall is parallel to the ridge line of the roof. This criteria helps us select the right wind table. 217

217 Design Example 2b - Wind Two stories braced (roof and level 2) Table 3.17B L = 10.6 ft Table 3.17B in this case. Locate on the left hand drawings of the table where the wall of interest with respect to the building. The intersection of the building width W and the design wind speed gives the required length of shearwall, L. This L is for a shearwall 8 ft high. 218

218 Design Example 2b - Wind Minimum Length Full Height Sheathing - Type I Wall L Type1 = L C WH = (10.6) (1.125) = ft < 28 ft shearwall panels provided OK Now we adjust L by multiplying it by C WH for the 9ft wall height, to get the length of shearwall required. 219

219 Design Example 2a & b - Type II Walls 6 9 Exterior Type II Shearwalls (perforated) (WFCM ) north elevation Length of wall (L wall ) 40 ft Length of full height sheathing (L full height ) 28 ft % Full Height Sheathing (L wall /L full height ) 70% Maximum unrestrained opening height 6 ft shaded areas show potential eligible shearwall panels If it is desired to use perforated shearwalls as a solution, the additional design steps are minimal. You must determine Type I length requirements first. From the wall elevation, determine the % of full wall sheathing, and the maximum unrestrained opening height (window or door). This data is needed to enter

220 Design Example 2a & b - Type II Walls Table 3.17E Type II increase factor = 1.18.Table 3.17E to calculate the Type II wall increase factor. At the top left of the table, from the intersection of the shearwall height and maximum unrestrained opening, read down to the intersection of the % full height sheathing value (blue). Read off the increase factor. 221

221 Design Example 2a & b - Type II Wall Minimum Length Full Height Sheathing (ft) - Type II Wall L TypeII = L TypeI C L Wind Seismic L TypeI C L L TypeII ft ft Table 3.17E Multiply the increase factor by the required Type I wall lengths from before to get required wall lengths for Type II perforated shearwalls. 222

222 Design Example 2a & b - Summary Minimum Length Full Height Sheathing Level 2 Wall North Elevation Type I segmented Type II perforated Seismic Wind Seismic Wind 19.4 ft ft ft ft The longest wall here will drive the lateral design which in this case is caused by seismic forces. Once we collect all this data, we see that we have sufficient wall length (28 ft) to accommodate all these possibilities. This design appears to be seismically-driven (largest required length) with Type II length requirements slightly higher than Type I. 223

223 Design Example 2a & b - Solution Assembly details for these panels as described in 2001 WFCM d common 6 OC on panel perimeter 8d common 12 OC in field 7/16 wood structural panel continuous height over wall plates panel exterior 5d cooler 7 OC on panel perimeter 5d cooler 10 OC in field 1/2 gypsum wallboard on interior panel interior Remember, here are the wall assembly assumptions used for the development of our solution so far based on the standard shear wall the default wall design. A cooler nail is also known as a drywall nail. It s quite unlikely this wall will ever be built this way in the field. 224

224 Wall Design Modification Want a different shearwall design? Choose one from Table 3.17 D and modify the capacity accordingly If you don t want the default wall, other walls are available with associated wall length modification factors for wind and seismic loads from Table 3.17D. Application of this information is as easy as multiplying the calculated required default wall length by the length modification factor for your wall of interest from the Table. 225

225 Wall Design Modification Alternative assembly details for these panels are available from Table 3.17D which modify the wall lengths with factors accordingly. 8d common 6 OC on panel perimeter 8d common 12 OC in field 7/16 wood structural panel continuous height over wall plates panel exterior Modified wall length = standard wall length x Table 3.17D factor (wind or seismic).and we can modify them through the use of Table 3.17D (see WFCM Workbook for a detailed example). 226

226 Design Example 2a & b - Solution and don t forget the holdowns from 2001 WFCM and don t forget the holdowns. You ll find a handy table in 2001 WFCM Table 3.17F. 227

227 Design Example 2a & b - Solution A selection of sliding/uplift anchorage design aids are found here: Wind (Exposure B) Table 3.2 Sill or Bottom Plate Connections (plf capacity) Table 3.2A Wind Shear Loads - 1/2 & 5/8 Anchor Bolts (numbers of bolts in shearwall line) Table 3.2B Wind Shear Loads - 1/2 & 5/8 Anchor Bolts (bolt spacing) Table 3.2C Wind Uplift Loads (bolt spacing) Table 3.4 Rafter/Truss Connections (lbs. capacity) Seismic Table 3.3 Sill or Bottom Plate Connections (lbs. capacity) Table 3.3A Seismic Shear Loads - 1/2 & 5/8 Anchor Bolts (bolt spacing) Here s a handy list for referencing design aids for anchorage against wall sliding and/or uplift. Roof/truss anchorage are also included in the Table 3.x list, among other assembly connections. Many of these tables will give a connector capacity, or a connector spacing as a result. 228

228 Presentation Summary Purpose & Background Development process Code Acceptance Document layout Design provisions: Wind Snow Seismic Design Examples Snow Design Wind shearwall design Seismic shearwall design This concludes all the topics presented here. 229

229 More information... Wood Frame Construction Manual 2001 Edition detailed calculations design examples graphics available now! The new 2001 WFCM Provisions and Commentary is available now. If you tend to design one- and two-family housing, this is a design resource that should be on your reference desk. 230

230 More information... Design of Wood Frame Buildings for High Wind, Snow and Seismic Loadings (workbook) real design example detailed calculations checklists blank worksheets for your use download free! This Wood Frame Construction Manual Workbook (WFCM Workbook) provides a design example, typical checklist, and background information related to design of a wood-frame structure in accordance with AF&PA s Wood Frame Construction Manual (WFCM) for One and Two-Family Dwellings, 2001 Edition. The design example uses plans from a 2-story residence designed to resist wind, seismic and snow loads. Typically, these load conditions do not all apply to the same structure (e.g., usually only 2 of these conditions are evaluated depending on the geographic location and local building code requirements). However, all three load conditions are evaluated in this example to show the broader range of applicability of the WFCM. The authority having jurisdiction should be consulted for applicable load conditions. The design example is based primarily on prescriptive provisions found in Chapter 3 of the WFCM. References to page numbers, tables and section numbers are for those found in the 2001 WFCM, unless noted otherwise. Additional engineering provisions or alternate solutions are provided where necessary. 231

231 3 Prescriptive Design Here is an isometric view of the house designed in the WFCM Workbook. 232

232 3 Prescriptive Design The WFCM Workbook is filled with very useful tables, checklists, and instructional aids. All tables are fully referenced to the standard. Blank worksheets are provided for future use. 233

233 3 Prescriptive Design The checklists are complete so that nothing is left out of the design 234

234 3 Prescriptive Design and are arranged by system 235

235 3 Prescriptive Design the same way the WFCM is laid out. 236

236 3 Prescriptive Design Full documentation aids are included, for loads 237

237 3 Prescriptive Design and displacement limits. 238

238 3 Prescriptive Design Assembly plan and elevation views are shown. 239

239 3 Prescriptive Design Blank Tables are included for rafter design 240

240 3 Prescriptive Design as well as a completed table example. 241

241 3 Prescriptive Design Same for ceiling/floor framing blank 242

242 3 Prescriptive Design and completed. 243

243 3 Prescriptive Design Table for floor sheathing design. 244

244 3 Prescriptive Design Table for load-bearing wall stud design blank

245 3 Prescriptive Design and completed. 246

246 3 Prescriptive Design Table for top plate design, including splicing points blank 247

247 3 Prescriptive Design and completed. 248

248 WFCM-2001 Header Example: 60 psf ground snow load 90 mph wind speed (3-second gust) bldg width 36 feet exterior load bearing wall header, supporting roof, ceiling, and one center-bearing wall header span of 6 feet Here is a short header design example taken out of the WFCM Workbook. Design info is as displayed in the slide. 249

249 WFCM-2001 Section Headers, p.113- Maximum spans for common species of lumber headers... shall not exceed the lesser of... spans in Tables 3.22A-E and Table 3.23A The number of jack studs at each end given in Table 3.22F The number of full height studs at each end of header given in Table 3.23C Here is the WFCM verbage on header design, and how to proceed. 250

250 3 Prescriptive Design The WFCM Workbook makes it easy by consolidated the design process into a handy table. 251

251 WFCM-2001, p.187 First, we determine the gravity load resistance of the header from Table 3.22B. Using the blue inputs, we come out of the Table with the solution in orange: 3-2x12 s. 252

252 WFCM-2001, p.192 Now we check out-of-plane loading (wind) in Table 3.23A, again using the blue inputs to the table. The solution (in orange) is: 3 2x12 s, same as before. If a results are different between the two tables, the larger result will govern the design. 253

253 WFCM-2001 Section Headers- Maximum spans for common species of lumber headers... shall not exceed the lesser of... spans in Tables 3.22A-E and Table 3.23A The number of jack studs at each end given in Table 3.22F The number of full height studs at each end of header given in Table 3.23C Now we need to determine the framing needed to support the header. WFCM shows us where to go 254

254 WFCM-2001 and illustrations clearly identify all the needed parts. 255

255 WFCM-2001 Gravity The Jack Studs support the header carrying gravity load, and these studs are continuous from the underside of the header to the bottom plate of the wall. Using the blue inputs to Table 3.22F, the solution in orange requires: 3 Jack Studs at each end of the header. 256

256 WFCM-2001 Lateral Out-of-Plane Out-of-plane loads on the header (from wind) need to transfer from the header into the wall framing. Full height (King) studs next to the header ends, and Jack Studs, are used to do this. The King Studs act like a point loaded (from the header) beam. Using the inputs in blue to the King Stud Table 3.23C gives: 6 King Studs required at each end of the header. While this might seem excessive, consider the load: 120 MPH wind!!! The design gets even more interesting if the header is dropped in height from the wall top plate! 257

257 Wall Header Solution All of this information is summarized neatly in the WFCM Workbook header table. Additions to this table include sill plate design due to out-of-plane loading (wind). 258

258 New! - Hot off the press!!! Guide(s) to Wood Construction in High Wind Areas AF&PA s newest design standard has just been developed (2006). By request, AF&PA developed five handy Guides to Wood Construction in High Wind Areas, one for each wind speed from 90 to 130 mph. These Guides fully illustrated in full color provide simplified extractions of design information right out of the 2001 WFCM. 259

259 Engineering Standards Guide(s) to Wood Construction in High Wind Areas Individual, easy-to-use Guides addressing wind design in 90, 100, 110, 120, and 130 mph wind zones. Based on provisions contained in AF&PA's Wood Frame Construction Manual (WFCM) for One- and Two-Family Dwellings, 2001 Edition. Use of the high wind provisions of these Guides will result in designs that meet the requirements of the WFCM and the IRC. Guides are free for downloading from These Guides fully illustrated in full color provide simplified extractions of design information right out of the 2001 WFCM. They are completely free of charge and downloadable from 260

260 Guide - Layout 1. General Provisions 2. Foundation Anchorage 3. Floors 4. Walls 5. Roofs Glossary of Terms Checklist Each Guide is laid out in in the same fashion as the 2001 WFCM: by system assembly. 261

261 Guide General Provisions Verbal and graphical presentations Color illustrations and large text add to the user-friendly nature of these design tools. 262

262 Guide General Provisions Tables delineate building aspect ratios and widths. Tables are easy to read and interpret. 263

263 Guide Foundation Anchorage In some cases, tables are tied to explanatory graphics. 264

264 Guide - Floors Figures illustrate cantilever limits and floor bracing. Another example. 265

265 Guide - Walls Illustrations and tables explain wall construction. Wall design tables are straight forward 266

266 Guide - Walls and sheathing attachment for lateral resistance. following in the same fashion as the 2001 WFCM. 267

267 Guide - Roofs Illustration explains forces and spans The emphasis on complete load path is apparent. 268

268 Guide - Checklist Checklist is included to assist in code compliance. Handy checklists complete each Guide. 269

269 More information... For more information on this and other subjects, and how to order WFCM, see the AWC website at or call the AWC publications department toll-free at

270 Questions? Online ecourses FAQ s HelpDesk AWCinfo@afandpa.org (202) or (800) Comments AWC_education@afandpa.org This concludes this approved continuing education program. 271