Shear Wall Design Manual

Transcription

1 Shear Wall Design Manual IS 456:2000 & 13920:1993

2 Shear Wall Design Manual IS 456:2000 and IS 13920:1993 For ETABS 2016 ISO ETA122815M47 Rev. 0 Proudly developed in the United States of America December 2015

3 Copyright Copyright Computers & Structures, Inc., All rights reserved. The CSI Logo, SAP2000, ETABS, and SAFE are registered trademarks of Computers & Structures, Inc. Watch & Learn TM is a trademark of Computers & Structures, Inc. The computer programs SAP2000 and ETABS and all associated documentation are proprietary and copyrighted products. Worldwide rights of ownership rest with Computers & Structures, Inc. Unlicensed use of these programs or reproduction of documentation in any form, without prior written authorization from Computers & Structures, Inc., is explicitly prohibited. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior explicit written permission of the publisher. Further information and copies of this documentation may be obtained from: Computers & Structures, Inc. info@csiamerica.com (for general information) support@csiamerica.com (for technical support)

4 DISCLAIMER CONSIDERABLE TIME, EFFORT AND EXPENSE HAVE GONE INTO THE DEVELOPMENT AND TESTING OF THIS SOFTWARE. HOWEVER, THE USER ACCEPTS AND UNDERSTANDS THAT NO WARRANTY IS EXPRESSED OR IMPLIED BY THE DEVELOPERS OR THE DISTRIBUTORS ON THE ACCURACY OR THE RELIABILITY OF THIS PRODUCT. THIS PRODUCT IS A PRACTICAL AND POWERFUL TOOL FOR STRUCTURAL DESIGN. HOWEVER, THE USER MUST EXPLICITLY UNDERSTAND THE BASIC ASSUMPTIONS OF THE SOFTWARE MODELING, ANALYSIS, AND DESIGN ALGORITHMS AND COMPENSATE FOR THE ASPECTS THAT ARE NOT ADDRESSED. THE INFORMATION PRODUCED BY THE SOFTWARE MUST BE CHECKED BY A QUALIFIED AND EXPERIENCED ENGINEER. THE ENGINEER MUST INDEPENDENTLY VERIFY THE RESULTS AND TAKE PROFESSIONAL RESPONSIBILITY FOR THE INFORMATION THAT IS USED.

5 Contents Shear Wall Design 1 Introduction 1.1 Notation Design Station Locations Default Design Load Combinations Dead Load Component Live Load Component Wind Load Component Earthquake Load Component Combinations that Include a Response Spectrum Combinations that Include Time History Results Combinations that Include Static Nonlinear Results Design Strength Shear Wall Design Preferences Shear Wall Design Overwrites Choice of Units 1-16 Contents - i

6 Shear Wall Design IS 456:2000 and IS 13920: Pier Design 2.1 Wall Pier Flexural Design Checking a General or Uniform Reinforcing Pier Section Designing a Simplified T and C Pier Section Wall Pier Boundary Elements Details of Check for Boundary Element Requirements Transverse Reinforcement for Boundary Elements Wall Pier Shear Design Determine Factored Shear Force Determine the Concrete Shear Capacity Determine the Required Shear Reinforcing Spandrel Design 3.1 Spandrel Flexural Design Determine the Maximum Factored Moments Determine the Required Flexural Reinforcing Spandrel Shear Design Determine Factored Shear Force Determine Concrete Shear Capacity Determine Required Shear Reinforcement Spandrel Diagonal Reinforcement 3-17 Appendix A Shear Wall Design Preferences Appendix B Design Procedure Overwrites Appendix C Analysis Sections and Design Sections References ii - Contents

7 Chapter 1 Introduction This chapter describes in detail the various aspects of the shear wall design procedure that is used by the program when the user selects the Indian IS code option. This covers the basic design code IS 456:2000 Indian Standard Plain and Reinforced Concrete Code of Practice (IS 2000), the seismic code IS 13920:1993 (Reaffirmed 1998, Edition 1.2, ), Indian Standard Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces Code of Practice (IS 2002), and a part of the draft seismic code (Jain and Murty 2008). Various notation used in this chapter are listed in Section 1.1. For referencing to the pertinent sections of the Indian codes in this manual, a prefix IS followed by the section number is used. The relevant prefixes are IS, IS 13920, and IS Draft for the basic code IS 456:2000, the seismic code IS 13920:1993, and the draft seismic code, respectively. English as well as SI and MKS metric units can be used for input. The code is based on Millimeter-Newton-Second units. For simplicity, all equations and descriptions presented in this chapter correspond to Millimeter-Newton-Second units unless otherwise noted. The design is based on loading combinations specified by the user. To facilitate the design process, the program provides a set of default load combinations that should satisfy requirements for the design of most building type structures (Section 1.3). 1-1

8 Shear Wall Design IS 456:2000 and IS13920:1993 The program performs the following design, check, or analysis procedures in accordance with IS 456:2000 and IS 13920:1993 requirements: Design and check of concrete wall piers for flexural and axial loads (Chapter 2) Design of concrete wall piers for shear (Chapter 2) Design of concrete shear wall spandrels for flexure (Chapter 3) Design of concrete wall spandrels for shear (Chapter 3) Consideration of the boundary element requirements for concrete wall piers using an approach based on the requirements of Section 9.4 in IS 13920:1993 (Chapter 2) The program provides detailed output data for Simplified pier section design, Section Designer pier section design, Section Designer pier section check, and spandrel design (Chapter 4). 1.1 Notation This section provides the notations used in this manual. A cv Net area of a wall pier bounded by the length of the wall pier, L w, and the web thickness, t p, mm 2 A g Gross area of a wall pier, mm 2 A h-min Minimum required area of distributed horizontal reinforcing steel required for shear in a wall spandrel, mm 2 /mm A s Area of reinforcing steel, mm 2 A' s Area of compression reinforcement, mm 2 A sc Area of reinforcing steel required for compression in a pier edge member, or the required area of tension steel required to balance the compression steel force in a wall spandrel, mm Notation

9 Chapter 1 - Introduction A sc-max A sf A st A st-max A sv /S v A vd A v-min A sw Maximum area of compression reinforcing steel in a wall pier edge member, mm 2 The required area of tension reinforcing steel for balancing the concrete compression force in the extruding portion of the concrete flange of a T-beam, mm 2 Area of reinforcing steel required for tension in a pier edge member, mm 2 Maximum area of tension reinforcing steel in a wall pier edge member, mm 2 Area of reinforcing steel required for shear pier unit length, mm 2 /mm Area of diagonal shear reinforcement in a coupling beam, mm 2 Minimum required area of distributed vertical reinforcing steel required for shear in a wall spandrel, mm 2 /mm The required area of tension reinforcing steel for balancing the concrete compression force in a rectangular concrete beam, or for balancing the concrete compression force in the concrete web of a T-beam, mm 2 A' s Area of compression reinforcing steel in a spandrel, mm 2 B 1, B 2,... C c Length of a concrete edge member in a wall with uniform thickness, mm Concrete compression force in a wall pier or spandrel, Newton C f Concrete compression force in the extruding portion of a T- beam flange, Newton C s Compression force in wall pier or spandrel reinforcing steel, Newton Notation 1-3

10 Shear Wall Design IS 456:2000 and IS13920:1993 C w D D f D/C DB1 DB2 Concrete compression force in the web of a T-beam, Newton Overall depth of a spandrel, mm Flange thickness in a T-beam spandrel, mm Demand/capacity ratio as measured on an interaction curve for a wall pier, unitless Length of a user-defined wall pier edge member, mm. This can be different on the left and right sides of the pier, and it also can be different at the top and the bottom of the pier. Width of a user-defined wall pier edge member, mm. This can be different on the left and right sides of the pier, and it also can be different at the top and the bottom of the pier. E c Modulus of elasticity of concrete, N/mm 2 E s Modulus of elasticity of reinforcement, assumed as 200,000 N/mm 2 H w IP-max IP-min L BZ LL L s L w Height of a wall spandrel, mm. This can be different on the left and right ends of the spandrel. The maximum ratio of reinforcing considered in the design of a pier with a Section Designer section, unitless The minimum ratio of reinforcing considered in the design of a pier with a Section Designer section, unitless Horizontal length of the boundary zone at each end of a wall pier, mm Live load Horizontal length of wall spandrel, mm Horizontal length of wall pier, mm. This can be different at the top and the bottom of the pier 1-4 Notation

11 Chapter 1 - Introduction M n M single M u M uc M uf M us M uw OC OL P b PC max Nominal bending strength, N-mm Design moment resistance of a section as a singly reinforced section, N-mm Ultimate factored design moment at a section object, N-mm In a wall spandrel with compression reinforcing, the factored bending moment at a design section resisted by the couple between the concrete in compression and the tension steel, N-mm In a wall spandrel with a T-beam section and compression reinforcing, the factored bending moment at a design section resisted by the couple between the concrete in compression in the extruding portion of the flange and the tension steel, N-mm In a wall spandrel with compression reinforcing, the factored bending moment at a design section resisted by the couple between the compression steel and the tension steel, N-mm In a wall spandrel with a T-beam section and compression reinforcing, the factored bending moment at a design section resisted by the couple between the concrete in compression in the web and the tension steel, N-mm On a wall pier interaction curve the distance from the origin to the capacity associated with the point considered On a wall pier interaction curve the distance from the origin to the point considered The axial force in a wall pier at a balanced strain condition, Newton Maximum ratio of compression steel in an edge member of a wall pier, unitless Notation 1-5

12 Shear Wall Design IS 456:2000 and IS13920:1993 P left P max P max Factor P n P O P oc P ot P right P u PT max RLL T s V c V n V s Equivalent axial force in the left edge member of a wall pier used for design, pounds. This may be different at the top and the bottom of the wall pier. Limit on the maximum compressive design strength specified by IS 456:2000, Newton Factor used to reduce the allowable maximum compressive design strength, unitless. IS 13920:1993 specifies this factor to be This factor can be revised in the preferences. Nominal axial strength, Newton Nominal axial load strength of a wall pier, Newton The maximum compression force a wall pier can carry with strength reduction factors set equal to one, Newton The maximum tension force a wall pier can carry with strength reduction factors set equal to one, Newton Equivalent axial force in the right edge member of a wall pier used for design, pounds. This may be different at the top and the bottom of the wall pier. Factored axial force at a design section, Newton Maximum ratio of tension steel in an edge member of a wall pier, unitless Reduced live load Tension force in wall pier reinforcing steel, Newton The portion of the shear force carried by the concrete, Newton Nominal shear strength, Newton The portion of the shear force in a spandrel carried by the shear reinforcing steel, Newton 1-6 Notation

13 Chapter 1 - Introduction V u WL b f b s d d' d compression d r-bot d r-top d s d spandrel Shear force of ultimate design load, Newton Wind load Width or effective width of flange in a flanged spandrel beam, mm Width of the compression flange in a T-beam, mm. This can be different on the left and right end of the T-beam. Effective depth of tension reinforcement in a spandrel, mm Effective depth of compression reinforcement, mm Depth of center of compression block from most compressed face, mm Distance from bottom of spandrel beam to centroid of the bottom reinforcing steel, inches. This can be different on the left and right ends of the beam. Distance from top of spandrel beam to centroid of the top reinforcing steel, mm. This can be different on the left and right ends of the beam. Depth of the compression flange in a T-beam, mm. This can be different on the left and right ends of the T-beam. Depth of spandrel beam minus cover to centroid of reinforcing, mm f cd Design concrete strength = f ck/γ c, N/mm 2 f ck Characteristic compressive strength of concrete, N/mm 2 f s Stress in compression steel of a wall spandrel, N/mm 2 f y Characteristic strength of reinforcement, N/mm 2 f yd Design yield strength of reinforcing steel = f y /γ s, N/mm 2 f ys Characteristic strength of shear reinforcement, N/mm 2 Notation 1-7

14 Shear Wall Design IS 456:2000 and IS13920:1993 k Enhancement factor of shear strength for depth of the beam m Normalized design moment, M u /αf ckdb 2 p max p min sv tp ts x u x u,max z α β δ ε Maximum ratio of reinforcing steel in a wall pier with a Section Designer section that is designed (not checked), unitless. Minimum ratio of reinforcing steel in a wall pier with a Section Designer section that is designed (not checked), unitless. Spacing of the shear reinforcement along the length of the spandrel beam, mm Thickness of a wall pier, mm. This can be different at the top and bottom of the pier. Thickness of a wall spandrel, mm. This can be different on the left and right ends of the spandrel. Depth of neutral axis, mm Maximum permitted depth of neutral axis, mm Lever arm, mm Concrete strength reduction factor for sustained loading Factor for the depth of compressive force resultant of the concrete stress block Enhancement factor of shear strength for compression Reinforcing steel strain, unitless ε c,max Maximum concrete strain in the beam and slab (= ) ε s ε s' Strain in tension steel Strain in compression steel 1-8 Notation

15 Chapter 1 - Introduction γ c γ f γ m γ s Partial safety factor for concrete strength Partial safety factor for load Partial safety factor for material strength Partial safety factor for steel strength σ s Reinforcing steel stress in a wall pier, N/mm 2 ρ Tension reinforcement ratio, A s /bd τ c Basic design shear stress resisted by concrete, N/mm 2 τ c,max Maximum possible design shear stress permitted at a section, MPa τ cd Design shear stress resisted by concrete, N/mm 2 τ v Average design shear stress resisted by the section, N/mm Design Station Locations The program designs wall piers at stations located at the top and bottom of the pier only. To design at the mid-height of a pier, break the pier into two separate half-height piers. The program designs wall spandrels at stations located at the left and right ends of the spandrel only. To design at the mid-length of a spandrel, break the spandrel into two separate half-length piers. Note that if you break a spandrel into pieces, the program will calculate the seismic diagonal shear reinforcing separately for each piece. The angle used to calculate the seismic diagonal shear reinforcing of each piece is based on the length of the piece, not the length of the entire spandrel. This can cause the required area of diagonal reinforcing to be significantly underestimated. Thus if you break a spandrel into pieces, calculate the seismic diagonal shear reinforcing separately by hand. Design Station Locations 1-9

16 Shear Wall Design IS 456:2000 and IS13920: Default Design Load Combinations The design loading combinations are the various combinations of the prescribed response cases for which the structure is to be checked/designed. The program creates a number of default design load combinations for a concrete frame design. Users can add their own design load combinations as well as modify or delete the program default design load combinations. An unlimited number of design load combinations can be specified. To define a design load combination, simply specify one or more response cases, each with its own scale factor. The scale factors are applied to the forces and moments from the analysis cases to form the factored design forces and moments for each design load combination. There is one exception to the preceding. For spectral analysis model combinations, any correspondence between the signs of the moments and axial loads is lost. The program uses eight design load combinations for each such loading combination specified, reversing the sign of axial loads and moments in major and minor directions. As an example, if a structure is subjected to dead load, D, and live load, L, only, the IS 456:2000 design check may need one design load combination only, namely, 1.5 D+1.5 L. However, if the structure is subjected to wind, earthquake or other loads, numerous additional design load combinations may be required. For the IS 456:2000 code, if a structure is subjected to dead (D), live (L), pattern live (PL), wind (W), and earthquake (E) loads, and considering that wind and earthquake forces are reversible, the following load combinations may need to be defined (IS , Table 18): 1.5D (IS ) 1.5D + 1.5L (IS ) 1.5D + 1.5(0.75PL) (IS ) 1.5D ± 1.5W 0.9D ± 1.5W (IS ) 1.2D ± 1.2L ± 1.2W 1.5D ± 1.5E 0.9D ± 1.5E (IS ) 1.2D + 1.2L ± 1.2E 1-10 Default Design Load Combinations

17 Chapter 1 - Introduction In the preceding equations, D = L = W = the sum of all dead load (DL) cases defined for the model. The sum of all live load (LL) and reducible live load (RLL) cases defined for the model. Note that this includes roof live loads as well as floor live loads. Any single wind load (WL) case defined for the model. E = Any single earthquake load (E) case defined for the model. These are also the default load combinations in the program whenever the Indian IS code is used. The user should use other appropriate design load combinations if roof live load is separately treated, or if other types of loads are present. The pattern loading is approximately, but conservatively, performed in the program automatically. Here PL is the approximate pattern load that is the live load multiplied by the Pattern Live Load Factor. The Pattern Live Load Factor can be specified in the Preferences. While calculating forces for the specified pattern load combination, the program adds forces for the dead load, assuming that the member geometry and continuity are unchanged from the model, and the forces for the pattern live load, assuming the beam is simply supported at the two ends. The Pattern Live Load Factor normally should be taken as 0.75 (IS ). If the Pattern Live Load Factor is specified to be zero, the program does not generate pattern loading. Live load reduction factors can be applied to the member forces of the load case that has a live load on a member-by-member basis to reduce the contribution of the live load to the factored loading. However such a live load must be specified as type Reducible Live Load. For slender compression members, the code recommends the use of a second order frame analysis, also called a P- analysis, which includes the effect of sway deflections on the axial loads and moments in a frame. For an adequate and rational analysis, realistic moment curvature or moment rotation relationships should be used to provide accurate values of deflections and forces. The analysis also should include the effect of foundation rotation and sustained loads. Because of the complexity in the general second order analysis of frames, the code provides an approximate design method that takes into account the additional moments due to lateral deflections in columns (IS 39.7). See also Clause 38.7 of SP (IS 1993) for details. Default Design Load Combinations 1-11

18 Shear Wall Design IS 456:2000 and IS13920:1993 Hence, when using the Indian IS code, it is recommended that the user include the P-delta analysis. With this option, the program can capture the lateral drift effect, i.e., the global effect or P- effect, very nicely. But the program does not capture the local effect (P-δ effect) to its entirety because most often the column members are not meshed. To capture the local effects in columns, the program uses the approximate formula for additional moments as specified in the code (IS ). Two major parameters in calculating the additional moments are the effective length factors for major and minor axis bending. The effective length factors for columns are computed using a codespecified procedure (IS 25.2, Annex E, Wood 1974). If P- analysis is not included, the program calculates effective length factors, k, assuming the frame is a sway frame (sway unrestrained) (IS Annex E, Figure 27). However, if the P- analysis is included, the program assumes the member is prevented from further sway and assumes that the frame can be considered non-sway where k < 1 (IS Annex E, Figure 26). In that case, the program takes k equal to 1 conservatively. For piers, k is taken as Dead Load Component The dead load component of the default design load combinations consists of the sum of all dead loads multiplied by the specified factor. Individual dead load cases are not considered separately in the default design load combinations Live Load Component The live load component of the default design load combinations consists of the sum of all live loads, both reducible and nonreducible, multiplied by the specified factor. Individual live load cases are not considered separately in the default design load combinations Wind Load Component The wind load component of the default design load combinations consists of the contribution from a single wind load case. Thus, if multiple wind load cases are defined in the program model, each case will contribute multiple design load combinations, as given in section Default Design Load Combinations

19 Chapter 1 - Introduction Earthquake Load Component The earthquake load component of the default design load combinations consists of the contribution from a single earthquake load case. Thus, if multiple earthquake load cases are defined in the program model, each case will contribute multiple design load combinations, as given in Section 1.3. The earthquake load cases considered when creating the default design load combinations include all static load cases that are defined as earthquake loads and all response spectrum cases. Default design load combinations are not created for time history cases or for static nonlinear cases Combinations That Include a Response Spectrum In the program all response spectrum cases are assumed to be earthquake load cases. Default design load combinations are created that include the response spectrum cases. The output from a response spectrum is all positive. Any shear wall design load combination that includes a response spectrum load case is checked for all possible combinations of signs on the response spectrum values. Thus, when checking shear in a wall pier or a wall spandrel, the response spectrum contribution of shear to the design load combination is considered once as a positive shear and then a second time as a negative shear. Similarly, when checking moment in a wall spandrel, the response spectrum contribution of moment to the design load combination is considered once as a positive moment and then a second time as a negative moment. When checking the flexural behavior of a two-dimensional wall pier or spandrel, four possible combinations are considered for the contribution of response spectrum load to the design load combination. They are: +P and +M +P and M P and +M P and M Default Design Load Combinations 1-13

20 Shear Wall Design IS 456:2000 and IS13920:1993 where P is the axial load in the pier and M is the moment in the pier. Similarly, eight possible combinations of P, M2 and M3 are considered for threedimensional wall piers. Note that based on the preceding, equations with negative signs with earthquake load cases in Section 1.3 are redundant for a load combination with a response spectrum. For this reason, the program creates only default design load combinations based on the equations with positive factors with earthquake load cases. Default design load combinations using equations with negative factors with earthquake load cases are not created for response spectra Combinations that Include Time History Results The default shear wall design load combinations do not include any time history results. To include time history forces in a design load combination, define the load combination yourself. When a design load combination includes time history results, the design is performed for each step of the time history. If a single design load combination has more than one time history case in it, that design load combination is designed for the envelopes of the time histories Combinations That Include Static Nonlinear Results The default shear wall design load combinations do not include any static nonlinear results. To include static nonlinear results in a design load combination, define the load combination yourself. If a design load combination includes a single static nonlinear case and nothing else, the design is performed for each step of the static nonlinear analysis. Otherwise, the design is only performed for the last step of the static nonlinear analysis Default Design Load Combinations

21 Chapter 1 - Introduction 1.4 Design Strength The design strengths for concrete and steel are obtained by dividing the characteristic strength of the material by a partial factor of safety, γ m. The values of γ m used in the program are as follows: Partial safety factor for steel, γ s = 1.15, and (IS ) Partial safety factor for concrete, γ c = (IS ) These factors are already incorporated in the design equations and tables in the code. Although not recommended, the program allows the defaults to be overwritten. If the defaults are overwritten, the program uses the revised values consistently by modifying the code mandated equations in every relevant place. 1.5 Shear Wall Design Preferences The shear wall design preferences are basic properties that apply to all wall pier and spandrel elements. Appendix B identifies shear wall design preferences for Indian IS For other codes, design preferences are set in a similar fashion. Default values are provided for all shear wall design preference items. Thus, it is not required that preferences be specified. However, at least review the default values for the preference items to make sure they are acceptable. Refer to Appendix A for details. 1.6 Shear Wall Design Overwrites The shear wall design overwrites are basic assignments that apply only to those piers or spandrels to which they are assigned. The overwrites for piers and spandrels are separate. Appendix C identifies the shear wall overwrites for Indian IS For other codes design preferences are set in a similar fashion. Note that the available overwrites change depending on the pier section type (Uniform Reinforcing, General Reinforcing, or Simplified T and C). Default values are provided for all pier and spandrel overwrite items. Thus, it is not necessary to specify or change any of the overwrites. However, at least review the default values for the overwrite items to make sure they are acceptable. When changes are made to overwrite items, the program applies the changes only to the elements to which they are specifically assigned; that is, to Design Strength 1-15

22 Shear Wall Design IS 456:2000 and IS13920:1993 the elements that are selected when the overwrites are changed. Refer to Appendix B for details. 1.7 Choice of Units For shear wall design in this program, any set of consistent units can be used for input. Also, the system of units being used can be changed at any time. Typically, design codes are based on one specific set of units. The IS 456:2000 and IS 13920:1993 codes are based on Newton-mm-Second units. For simplicity, all equations and descriptions presented in this manual correspond to Newton-mm-Second units unless otherwise noted. The shear wall design preferences allow the user to specify special units for concentrated and distributed areas of reinforcement. These units are then used for reinforcement in the model, regardless of the current model units displayed in the drop-down list on the status bar (or within a specific form). The special units specified for concentrated and distributed areas of reinforcing can only be changed in the shear wall design preferences. The choices available in the shear wall design preferences for the units associated with an area of concentrated reinforcing are in 2, cm 2, mm 2, and current units. The choices available for the units associated with an area per unit length of distributed reinforcing are in 2 /ft, cm 2 /m, mm 2 /m, and current units. The current units option uses whatever units are currently displayed in the drop-down list on the status bar (or within a specific form). If the current length units are cm, this option means concentrated areas of reinforcing are in cm 2 and distributed areas of reinforcing are in cm 2 /cm. Note that when using the current option, areas of distributed reinforcing are specified in Length 2 /Length units, where Length is the currently active length unit. For example, if you are working in KN and cm units, the area of distributed reinforcing is specified in cm 2 /cm. If you are in KN and mm, the area of distributed reinforcing is specified in mm 2 /mm. For details on general use of the program, refer to the CSi Analysis Reference Manual (CSI 2009) Choice of Units

23 Chapter 2 Pier Design This chapter describes how the program designs each leg of concrete wall piers for shear using the Indian IS code. It should be noted that in the program you cannot specify shear reinforcing and then have the program check it. The program only designs the pier for shear and reports how much shear reinforcing is required. The shear design is performed at stations at the top and bottom of the pier. This chapter also describes how the program designs and checks concrete wall piers for flexural and axial loads using the Indian IS code. First we describe how the program designs piers that are specified by a Simplified section. Next we describe how the program checks piers that are specified by a Section Designer section. Then we describe how the program designs piers that are specified by a Section Designer section. The program designs/checks only seismic or non-seismic reinforced concrete wall pier sections. Currently, other concrete wall pier design is not in the scope of the program. 2-1

24 Shear Wall Design IS 456:2000 and IS 13920: Wall Pier Flexural Design ETABS can design the pier sections that are defined as "General Reinforcing Pier sections or "Uniform Reinforcing Pier sections when reinforcing layout is given and "Design Reinforcement" is requested. The program can check those two types of sections when reinforcements are given and "Check Reinforcement" is requested. The program can design the pier sections that are defined as "Simplified T and C Pier sections. In all cases, P-M-M interaction is used for the overall section. For Simplified T and C sections, approximations are used to perform simple design. For the design problems, design reinforcement is reported. For the check problems, the P-M-M interaction ratio is reported. For flexural design/check of piers, the factored forces axial force P u, and the bending moments M u2 and M u3 for a particular design load combination at a particular design section (top or bottom) are obtained by factoring the associated forces and moments with the corresponding design load combination factors. The piers are designed for minimum eccentricity moment, P ue min, where e min = e min L = L L 30 w t 30 w (IS 25.4) where L w = t w = L 33 = Overall horizontal length of the wall, The thickness of the wall, Unbraced length of the wall in the major direction, = Story height, L 22 = Unbraced length of the wall in the minor direction, = Story height. The minimum eccentricity is applied in only one direction at a time (IS 25.4). 2-2 Wall Pier Flexural Design

25 Chapter 2 - Pier Design The program computes the slenderness ratios as L 33/L w and L 22/t w where L 33 and L 22 are effective lengths of column about local axes 3 and 2. If the slenderness ratio is greater than 12, the pier is considered as slender in that plane (IS ). Effectively, the pier may be slender in one or both planes. If a column is slender in a plane, additional slenderness moments M a2 and M a3 are computed using the following formula: M 2 PD u L33 a3 = k 2000 Lw (IS , ) M 2 Pb u L22 a2 = k 2000 tw (IS , ) where k Puz Pu = 1 P P uz b (IS ) P uz = 0.45 f cka c f ya sc (IS 39.6) M a2, M a3 = Additional moment t accounts for the column slenderness about the column local 2 and 3 axes, respectively P u = Factored axial force in the column for a particular load combination P uz = Theoretical axial capacity of the column P b = Axial load corresponding to the condition of maximum compressive strain of in concrete and tensile strain of in the outermost layer of tensile steel L 33, L 22 = Effective length of the column about the local 3 and 2 axes, respectively L 22 = k 22L 22 L 33 = k 33L 33 D, b = Lateral column dimension perpendicular to the local 3 and 2 axes, respectively Wall Pier Flexural Design 2-3

26 Shear Wall Design IS 456:2000 and IS 13920:1993 k = Reduction factor for reducing additional moments Other variables are described in Section 1.1 Notation in Chapter 1. When designing the pier, A sc is not known in advance, and thus P uz and P b are not known. In such cases, k is conservatively taken as 1. k = 1 The program assumes the effective length factors k 33 = 1 and k 22 = 1. The use of code-specified additional moment (IS 39.7) is an approximate procedure (IS SP-24, 1993, Clause 38.7). It is recommended that the user include P-Delta analysis. With this option, the program can capture the lateral drift effect (i.e., global effect or P- effect), but the program does not capture local effect (i.e., P-δ effect) to its entirety through analysis. To capture the local effect correctly, the program uses the approximate design formula for additional moments with the assumption that k = 1. It should be noted that the minimum eccentricity is enforced and additional moment is employed for a planar wall, as stated previously. However for multi-legged 3D piers, the minimum eccentricity is enforced based on equivalent thickness. Similar slenderness effects are calculated based on equivalent thickness Checking a General or Uniform Reinforcing Pier Section When you specify that a General Reinforcing or Uniform Reinforcing pier section is to be checked, the program creates an interaction surface for that pier and uses that interaction surface to determine the critical flexural demand/ capacity ratio for the pier. This section describes how the program generates the interaction surface for the pier and how it determines the demand/capacity ratio for a given design load combination. Note: In this program, the interaction surface is defined by a series of P-M-M interaction curves that are equally spaced around a 360-degree circle. 2-4 Wall Pier Flexural Design

27 Chapter 2 - Pier Design Interaction Surface In this program, a three-dimensional interaction surface is defined with reference to the P, M 2 and M 3 axes. The surface is developed using a series of interaction curves that are created by rotating the direction of the pier neutral axis in equally spaced increments around a 360-degree circle. For example, if 24 P- M-M curves are specified (the default), there is one curve every 15 degrees (360 /24 curves = 15 ). Figure 2-1 illustrates the assumed orientation of the pier neutral axis and the associated sides of the neutral axis where the section is in tension (designated T in the figure) or compression (designated C in the figure) for various angles. T C 3 Interaction curve is for a neutral axis parallel to this axis Pier section T C 3 Interaction curve is for a neutral axis parallel to this axis Pier section 2 2 a) Angle is 0 degrees b) Angle is 45 degrees 45 3 Interaction curve is for a neutral axis parallel to this axis Pier section 3 Interaction curve is for a neutral axis parallel to this axis Pier section 2 2 C T a) Angle is 180 degrees 225 b) Angle is 225 degrees C T Figure 2-1: Orientation of the Pier Neutral Axis for Various Angles Note that the orientation of the neutral axis is the same for an angle of θ and θ Only the side of the neutral axis where the section is in tension or compression changes. We recommend that you use 24 interaction curves (or more) to define a three-dimensional interaction surface. Wall Pier Flexural Design 2-5

28 Shear Wall Design IS 456:2000 and IS 13920:1993 Each P-M-M interaction curve that makes up the interaction surface is numerically described by a series of discrete points connected by straight lines. The coordinates of these points are determined by rotating a plane of linear strain about the neutral axis on the section of the pier. Details of this process are described in the next section, Generation of the Biaxial Interaction Surface. By default, 11 points are used to define a P-M-M interaction curve. This number can be changed in the preferences; any odd number of points greater than or equal to 11 can be specified, to be used in creating the interaction curve. If an even number is specified for this item in the preferences, the program will increment up to the next higher odd number. Note that when creating an interaction surface for a two-dimensional wall pier, the program considers only two interaction curves the 0 curve and the 180 curve regardless of the number of curves specified in the preferences. Furthermore, only moments about the M3 axis are considered for two-dimensional walls Generation of the Biaxial Interaction Surface The column capacity interaction volume is numerically described by a series of discrete points that are generated on the three-dimensional interaction failure surface. In addition to axial compression and biaxial bending, the formulation allows for axial tension and biaxial bending considerations. A typical interaction diagram is shown in Figure 2-2. The coordinates of these points are determined by rotating a plane of linear strain in three dimensions on the section of the column, as shown in Figure 2-3. The linear strain diagram limits the maximum concrete strain, ε c, at the extremity of the section, as given by the following equations: (a) When there is any tensile strain in the section, the maximum strain in concrete at the outermost compression fiber is taken as (IS 38.1(b)). ε c = , when tensile strain is present (IS 38.1(b)) (b) When the section is uniformly compressed, the maximum compression strain in concrete is taken as (IS 39.1(a)). 2-6 Wall Pier Flexural Design

29 Chapter 2 - Pier Design Figure 2-2 A typical column interaction surface ε c = 0.002, when the section in uniformly compressed (IS 39.1(a)) (c) When the entire section is under non-uniform compression, the maximum compressive strain at the highly compressed extreme fiber is taken as minus 0.75 times the strain at the least compressed extreme fiber (IS 39.1(b)). ε c,max = ε c,min, when the section is nonuniformly compressed (IS 39.1(b)) The formulation is based consistently on the basic principles of limit state of collapse under compression and bending (IS 38, 39). The stress in the steel is given by the product of the steel strain and the steel modulus of elasticity, ε se s, and is limited to the design strength of the steel, f y / γ s (IS 38.1(e)). The area associated with each reinforcing bar is assumed to be placed at the actual location of the center of the bar, and the algorithm does Wall Pier Flexural Design 2-7

30 Shear Wall Design IS 456:2000 and IS 13920:1993 not assume any further simplifications with respect to distributing the area of steel over the cross-section of the column, as shown in Figure 2-3. Figure 2-3 Idealized strain distribution for generation of interaction surface The concrete compression stress block is assumed to be parabolic, with a stress value of 0.67 f ck γ m (IS 38.1.c). See Figure 2-4. The interaction algorithm provides corrections to account for the concrete area that is displaced by the reinforcement in the compression zone. 2-8 Wall Pier Flexural Design

31 Chapter 2 - Pier Design 0.67 f cu γ m x u d ε = c. ε s 2 ε 1 s 1 c s c 2 c s x u c = f ck x u f ck ε s 3 3 T s ε s 4 4 T s Concrete Section Strain Diagram Stress Diagram Figure 2-4 Idealization of stress and strain distribution in a column section The equivalent concrete compression stress block is assumed to be rectangular, with a stress value of 0.36 f ck [IS 38.1(c), Figure 22], as shown in Figure 2-4. The depth of the equivalent rectangular block, a, is taken as: a = β 1 x u (IS 38.1(c), Figure 22) where c is the depth of the stress block in compression strain, and β 1 = = (IS 38.1(c), Figure 22) The maximum compressive axial strength is limited to P u, where P u = [0.4f cka c f ya sc]. (IS 39.3) However, the preceding limit is not normally reached unless the section is heavily reinforced. Note: The number of points to be used in creating interaction diagrams can be specified in the shear wall preferences and overwrites. As previously mentioned, by default, 11 points are used to define a single interaction curve. When creating a single interaction curve, the program includes the points at P b, P oc and P ot on the interaction curve. Half of the remaining Wall Pier Flexural Design 2-9

32 Shear Wall Design IS 456:2000 and IS 13920:1993 number of specified points on the interaction curve occur between P b and P oc at approximately equal spacing along the P u axis. The other half of the remaining number of specified points on the interaction curve occur between P b and P ot at approximately equal spacing along the P u axis Wall Pier Demand/Capacity Ratio Refer to Figure 2-5, which shows a typical two-dimensional wall pier interaction diagram. The forces obtained from a given design load combination are P u and M u3. Point L, defined by (P u, M u3), is placed on the interaction diagram, as shown in the figure. If the point lies within the interaction curve, the wall pier capacity is adequate. If the point lies outside of the interaction curve, the wall pier is overstressed. P u C P u L Axial Compression Axial Tension O M u3 M u3 Figure 2-5: Two-Dimensional Wall Pier Demand/Capacity Ratio As a measure of the stress condition in the wall pier, the program calculates a stress ratio. The ratio is achieved by plotting the point L and determining the location of point C. Point C is defined as the point where the line OL (extended outward if needed) intersects the interaction curve. The demand/capacity ratio, D/C, is given by D/C = OL / OC where OL is the "distance" from point O (the origin) to point L and OC is the "distance" from point O to point C. Note the following about the D/C ratio: If OL = OC (or D/C = 1), the point (P u, M u3) lies on the interaction curve and the wall pier is stressed to capacity Wall Pier Flexural Design

33 Chapter 2 - Pier Design If OL < OC (or D/C < 1), the point (P u, M u3) lies within the interaction curve and the wall pier capacity is adequate. If OL > OC (or D/C > 1), the point (P u, M3 u) lies outside of the interaction curve and the wall pier is overstressed. The wall pier D/C ratio is a factor that gives an indication of the stress condition of the wall with respect to the capacity of the wall. The D/C ratio for a three-dimensional wall pier is determined in a similar manner to that described here for two-dimensional piers. The maximum of all the D/C ratios calculated for each design load combination is reported for each check station of the pier along with the controlling (P u, M u2, M u3) set and the associated load combination name Designing a General or Uniform Reinforcing Pier Section When a General Reinforcing pier section is specified to be designed, the program creates a series of interaction surfaces for the pier based on the following items: The size of the pier as specified in Section Designer. The location of the reinforcing specified in Section Designer. The size of each reinforcing bar specified in Section Designer relative to the size of the other bars. The interaction surfaces are developed for eight different ratios of reinforcingsteel-area-to-pier-area. The pier area is held constant and the rebar area is modified to obtain these different ratios; however, the relative size (area) of each rebar compared to the other bars is always kept constant. The smallest of the eight reinforcing ratios used is that specified in the shear wall design preferences as Section Design IP-Min. Similarly, the largest of the eight reinforcing ratios used is that specified in the shear wall design preferences as Section Design IP-Max. The eight reinforcing ratios used are the maximum and the minimum ratios plus six more ratios. The spacing between the reinforcing ratios is calculated as Wall Pier Flexural Design 2-11

34 Shear Wall Design IS 456:2000 and IS 13920:1993 an increasing arithmetic series in which the space between the first two ratios is equal to one-third of the space between the last two ratios. Table 1 illustrates the spacing, both in general terms and for a specific example, when the minimum reinforcing ratio, IP-Min, is and the maximum, IP-Max, is After the eight reinforcing ratios have been determined, the program develops interaction surfaces for all eight of the ratios using the process described earlier in this section. Next, for a given design load combination, the program generates a D/C ratio associated with each of the eight interaction surfaces. The program then uses linear interpolation between the eight interaction surfaces to determine the reinforcing ratio that gives a D/C ratio of 1 (actually the program uses the Utilization Factor Limits instead of 1; the Utilization Factor Limit is 0.95 by default, but it can be overwritten by the user in the preferences). This process is repeated for all design load combinations and the largest required reinforcing ratio is reported. Design of a Uniform Reinforcing pier section is similar to that described herein for the General Reinforcing section. Table 2-1 The Eight Reinforcing Ratios Used by the Program Curve Ratio, e Example, e 1 IPmin IPmax IPmin IPmin IPmax IPmin IPmin IPmax IPmin IPmin IPmax IPmin IPmin IPmax IPmin IPmin IPmax IPmin IPmin IPmax Wall Pier Flexural Design

35 Chapter 2 - Pier Design Designing a Simplified T and C Pier Section This section describes how the program designs a pier that is assigned a simplified section. The geometry associated with the simplified section is illustrated in Figure 2-6. The pier geometry is defined by a length, thickness and size of the edge members at each end of the pier (if any). The central idea behind simplified T and C pier section design is that the axial forces and moments are carried by only the wall pier end zones known as Boundary Elements, located at wall edges, which provide the moment of resistance by developing a tension-compression couple, under combined action of axial force and moment. The central part of the wall is ignored in strength computation and is provided with minimum throwaway reinforcement. This method results in a conservative design of the wall pier for axial force and flexure. A simplified T and C pier section is always planar (not three-dimensional). The dimensions shown in the figure include the following: The length of the wall pier is designated L w. This is the horizontal length of the wall pier in plan. The thickness of the wall pier is designated t p. The thickness specified for left and right edge members (DB2 left and DB2 right) may be different from this wall thickness. DB1 represents the horizontal length of the pier edge member. DB1 can be different at the left and right sides of the pier. However in symmetrical walls it is preferred to have them of same length. DB2 represents the horizontal width (or thickness) of the pier edge member. DB2 can be different at the left and right sides of the pier. The dimensions illustrated are specified in the shear wall overwrites (Appendix C), and can be specified differently at the top and bottom of the wall pier. Wall Pier Flexural Design 2-13

36 Shear Wall Design IS 456:2000 and IS 13920:1993 Figure 2-6: Typical Wall Pier Dimensions Used for Simplified Design If no specific edge member dimensions have been specified by the user, the program assumes that the edge member is the same width as the wall, and the program determines the required length of the edge member. In all cases, whether the edge member size is user-specified or program-determined, the program reports the required area of reinforcing steel at the center of the edge member. This section describes how the program-determined length of the edge member is determined and how the program calculates the required reinforcing at the center of the edge member. Three design conditions are possible for a simplified T and C wall pier. These conditions, illustrated in Figure 2-7, are as follows: The wall pier has program-determined (variable length and fixed width) edge members on each end. The wall pier has user-defined (fixed length and width) edge members on each end Wall Pier Flexural Design

37 Chapter 2 - Pier Design The wall pier has a program-determined (variable length and fixed width) edge member on one end and a user-defined (fixed length and width) edge member on the other end. Design Condition 1 Wall pier with uniform thickness and ETABS-determined (variable length) edge members Design Condition 2 Wall pier with user-defined edge members Design Condition 3 Wall pier with a user-defined edge member on one end and an ETABSdetermined (variable length) edge member on the other end Note: In all three conditions, the only reinforcing designed by ETABS is that required at the center of the edge members Figure 2-7: Design Conditions for Simplified Wall Piers Design Condition 1 Design condition 1 applies to a wall pier with uniform design thickness and program-determined edge member length. For this design condition, the design algorithm focuses on determining the required size (length) of the edge members, while limiting the compression and tension reinforcing located at the center of the edge members to user-specified maximum ratios. The maximum ratios are specified in the shear wall design preferences and the pier design overwrites as Edge Design PC-Max and Edge Design PT-Max. Consider the wall pier shown in Figure 2-8. For a given design section, for example the top of the wall pier, the wall pier for a given design load combination is designed for a factored axial force P u-top and a factored moment M u-top. The program initiates the design procedure by assuming an edge member at the left end of the wall of thickness t p and width B 1-left, and an edge member at the right end of the wall of thickness t p and width B 1-right. Initially B 1-left = B 1-right = t p. Wall Pier Flexural Design 2-15

38 Shear Wall Design IS 456:2000 and IS 13920: L w t p 0.5t p 0.5t p t p t p B 1-left B 1-right B2-left B 3-left B 2-right B 3-right L w C L Wall Pier Plan P left-top P u-top Mu-top P right-top Top of pier Left edge member Right edge member M u-bot Bottom of pier P left-bot P u-bot Wall Pier Elevation P right-bot Figure 2-8: Wall Pier for Design Condition Wall Pier Flexural Design

39 Chapter 2 - Pier Design The moment and axial force are converted to an equivalent force set P left-top and P right-top using the equations that follow. (Similar equations apply at the bottom of the pier.) P P left-top right-top Pu-top Mu-top = + 2 L 0.5B 0.5B w 1-left Pu-top Mu-top = 2 L 0.5B 0.5B w 1-left 1-right 1-right For any given loading combination, the net values for P left-top and P right-top could be tension or compression. Note that for dynamic loads, P left-top and P right-top are obtained at the modal level and the modal combinations are made, before combining with other loads. Also for design loading combinations involving SRSS, the P left-top and P right-top forces are obtained first for each load case before the combinations are made. If any value of P left-top or P right-top is tension, the area of steel required for tension, A st, is calculated as: A st = P. f γ y s (IS 38) If any value of P left-top or P right-top is compression, for section adequacy, the area of steel required for compression, A sc, must satisfy the following relationship. P= Pmax,factor[0.4 f ( A A ) f A ] (IS 39.3) ck g sc y sc where P is either P left-top or P right-top, A g = t pb 1 and the P max,factor is defined in the shear wall design preferences (the default is 0.80). In general, we recommend that you use the default value. Area of compression rebar is calculated as follows: A sc ( ) P Pmax,factor 0.4 fck A = 0.67 f 0.4 f y If A sc calculates as negative, no compression reinforcing is needed. ck g Wall Pier Flexural Design 2-17

40 Shear Wall Design IS 456:2000 and IS 13920:1993 The maximum tensile reinforcing to be packed within the t p times B 1 concrete edge member is limited by: A = PT t B st-max max p 1. Similarly, the compression reinforcing is limited by: A PC t B sc-max = max p 1. If A st is less than or equal to A st-max and A sc is less than or equal to A sc-max, the program will proceed to check the next loading combination; otherwise the program will increment the appropriate B 1 dimension (left, right or both, depending on which edge member is inadequate) by one-half of the wall thickness to B 2 (i.e., 0.5t p) and calculate new values for P left-top and P right-top resulting in new values of A st and A sc. This iterative procedure continues until A st and A sc are within the allowed steel ratios for all design load combinations. If the value of the width of the edge member B increments to where it reaches a value larger than or equal to L p /2, the iteration is terminated and a failure condition is reported. This design algorithm is an approximate, but convenient, algorithm. Wall piers that are declared overstressed using this algorithm could be found to be adequate if the reinforcing steel is user-specified and the wall pier is accurately evaluated using interaction diagrams Design Condition 2 Design condition 2 applies to a wall pier with user-specified edge members at each end of the pier. The size of the edge members is assumed to be fixed; that is, the program does not modify them. For this design condition, the design algorithm determines the area of steel required in the center edge members and checks if that area gives reinforcing ratios less than the user-specified maximum ratios. The design algorithm used is the same as described for condition 1; however, no iteration is required Design Condition 3 Design condition 3 applies to a wall pier with a user-specified (fixed dimension) edge member at one end of the pier and a variable length (program Wall Pier Flexural Design

41 Chapter 2 - Pier Design determined) edge member at the other end. The width of the variable length edge member is equal to the width of the wall. The design is similar to that which has previously been described for design conditions 1 and 2. The size of the user-specified edge member is not changed. Iteration occurs only on the size of the variable length edge member. 2.2 Wall Pier Boundary Elements Boundary elements are portions along the wall edges that are strengthened by longitudinal and transverse reinforcement. The wall pier boundary element requirement is checked when the design load combination involves only seismic load. Each planar leg of multi-legged wall piers is checked. Both edges of each planar leg are checked separately. The basis for boundary element calculation is Section 9.4 of IS The boundary element calculation is similar to the design of a pier leg assuming a Simplified C-T wall pier, as described earlier in this chapter. The program reports the horizontal extents of the boundary, suggested longitudinal rebar area, and the required transverse reinforcement Details of Check for Boundary Element Requirements The following procedure is used for checking the required boundary elements, and if needed, for designing the boundary elements: Calculate the factored forces P u, V u, and M u for the pier planar leg section. Retrieve the geometric properties of the leg: the height of the wall segment (story height) h w; length of the wall pier planar leg, L w; the thickness of the pier leg t p. Refer to Figure 2-6 earlier in this chapter for an illustration of the dimensions. Retrieve the material properties of the pier leg, f ck and f y. Calculate the stress at the two extreme ends. Assume linearized elastic stress distribution and gross section properties. Ignore rebar area A s and M uz. Wall Pier Boundary Elements 2-19

42 Shear Wall Design IS 456:2000 and IS 13920:1993 σ P Mu A t L u = ± w ( L 2) w 3 w 12 (IS ) If any of the stresses at the two ends are compressive and exceed the following limit σ > 0.2f ck, (IS ) boundary elements are required (IS ) If boundary elements are needed at any edge of the pier leg, calculate the length of the required boundary element, the required longitudinal rebar, and the required transverse rebar from the following procedure. If boundary elements are required for any edge of a pier leg, as determined by the previous steps, the determination of the horizontal length of the boundary and the required longitudinal rebar is similar to the procedure that has been described in Section Designing a Simplified T and C Pier Section (IS ). Refer to that section for the details. However the following points should be noted. The boundary width determination is based on the maximum rebar density as described by PT max and PT min. The boundary width determination is an iterative procedure. The boundary element axial compressive capacity is based on the "short column," for which the capacity is given in IS Section The P max factor is taken as 1 for boundary element calculation. The moment of resistance provided by the distributed vertical reinforcement across the wall section is ignored Transverse Reinforcement for Boundary Elements Where special boundary elements are required by IS:13920 Section 9.4, the program computes and reports the total cross-sectional area of rectangular hoop reinforcement as follows: 2-20 Wall Pier Boundary Elements

43 Chapter 2 - Pier Design A s sh f A ck g = 0.18h (IS ) f y Ak 2.3 Wall Pier Shear Design The wall pier shear reinforcing is designed for each of the design load combinations. The required area of reinforcing for in-plane horizontal shear is calculated for each planar leg of the pier and only at the ends of the pier (i.e., at the story level). In this program, wall pier legs are designed for major (in-plane) direction shear force only. Effects caused by minor direction shear (out-of-plane) force that may exist in the pier planar legs must be investigated by the user independent of the program. The following steps are involved in designing the shear reinforcing for a particular wall pier leg section for a particular design loading combination. Determine the factored forces P u and V u that are acting on the wall pier section. Note that P u is required for the calculation of τ cd. Determine the shear stress, τ cd, that can be carried by the concrete alone. Determine the required shear reinforcing, A sv/s v, to carry the balance of the shear force. The following two sections describe in detail the algorithms associated with the this process. The assumptions in designing the shear reinforcement are as follows: The pier planar leg section can be considered to be prismatic. The program does not adjust the shear force for non-prismatic pier legs (IS ). The effect on the concrete shear capacity of any concentrated or distributed load in the span of the pier leg between two diaphragms is ignored. Also, the effect of the direct support on the piers provided by the diaphragms is ignored. Wall Pier Shear Design 2-21

44 Shear Wall Design IS 456:2000 and IS 13920:1993 All shear reinforcement is assumed to be perpendicular to the longitudinal reinforcement. The effect of axial force is considered (IS ) Determine Factored Shear Force In the design of the shear reinforcement for pier planar legs, the shear forces and axial forces for a particular design load combination at a particular beam section are obtained by factoring the associated shear force and axial force with the corresponding design load combination factors. The section is essentially considered to be prismatic. If the section is nonprismatic and the depth varies with length, the program does not adjust the design shear force as recommended by the code (IS ). In that case, the user is expected to check the shear independently of the program Determine the Concrete Shear Capacity Given the design force V u and P u, the design shear stress that can be carried by concrete alone, τ cd, and the maximum limit of nominal shear stress in the wall, τ c,max, are calculated differently when the design load combination does not involve any seismic loading and when it does. When the design load combination does not involve any seismic load, the shear force carried by the concrete, V c, by planar legs of wall piers is calculated as follows (IS , ): Vc = τ cd A cv, where (IS ; IS 40.2) K1 fck (3.0 Hw / Lw ) for Hw Lw 1 τ cd = ( Hw Lw + 1) K2 fck K3 fck for Hw Lw > 1 ( Hw Lw 1) τ cd = Design shear strength of concrete in walls (IS ) A cv = Effective area of wall pier section under shear, taken as b wd w (IS ) b w = Thickness of wall pier planar leg, 2-22 Wall Pier Shear Design

45 Chapter 2 - Pier Design d w = Effective depth of wall pier taken as 0.8L w, (IS ) L w = Overall horizontal length of the wall, (IS ) K 1 = 0.2 (IS ) K 2 = (IS ) K 3 = 0.15 (IS ) For non-seismic load combinations, the absolute maximum limit on the nominal shear stress, τ c,max, is calculated as follows (IS ): τ c,max = 0.17 f ck. (IS ) When the design load combination involves any seismic load, the shear force carried by the concrete, V c, by planar legs of the wall piers is calculated as follows (IS ; IS 40.2): V c = τ A (IS ; IS 40.2) cd c v where : A cv = Effective area of wall pier section under shear, taken as t wd w b w = Thickness of wall pier planar leg, (IS ) d w = Effective depth of wall pier taken as 0.8L w, (IS ; IS ) L w = Overall horizontal length of the wall (IS ) τ cd = kδτ c, (IS 40.2 and IS ) Pu if Pu > 0, Under Compression δ= Ag fck 1 if Pu 0, Under Tension (IS ) k is always taken as 1, and (IS ) τ c is the basic design shear strength for concrete, which is given by IS Table 19. It should be mentioned that the value of γ c has already Wall Pier Shear Design 2-23

46 Shear Wall Design IS 456:2000 and IS 13920:1993 been incorporated in IS Table 19 (see Note in IS ). The following limitations are enforced in the determination of the design shear strength as is done in the Table A s 3 bd f ck 40 N/mm 2 (for calculation purposes only) The determination of τ c from Table 19 of the code requires two parameters: 100 s A A and fck. If 100 s become more than 3.0, τc is bd bd A calculated based on 100 s A = 3.0. If 100 s becomes less than bd bd A 0.15, τ c is calculated based on 100 s = Similarly, if fck is bd larger than 40 N/mm 2, τ c is calculated based on f ck = 40 N/mm 2. However, if f ck is less than 15 N/mm 2, τ c is reduced by a factor of f ck with a factor of ( ) If γ c is chosen to be different from 1.5, τ c is adjusted c 1.5 γ. For seismic load combinations, the absolute maximum limit on nominal shear stress, τ c,max is calculated in accordance with IS Table 20, which is reproduced in the table that follows (IS , Table 20): Maximum Shear Stress, τ c,max (N/mm 2 ) Concrete Grade M15 M20 M25 M30 M35 M40 τ c,max (N/mm 2 ) If f ck is between the limits, linear interpolation is used Wall Pier Shear Design

47 Chapter 2 - Pier Design 2.5 if fck < 15 fck if 15 fck < 20 5 fck if 20 fck 25 5 fck 25 τ c,max = if 25 fck < 30 5 fck if 30 fck < 35 5 fck if 35 fck < if fck 40 (IS ) Determine the Required Shear Reinforcing Given V u, the required shear reinforcing in the form of area within a spacing, s v, is given by the following: Calculate the design nominal shear stress as V u τ v = (IS ; IS ) twdw where, t w = Thickness of the wall pier planar leg, d w = Effective depth of the wall pier planar leg, = 8 L w (IS ; IS ) L w = Overall horizontal length of the wall pier planar leg. Calculate the design permissible nominal shear stress, τ cd, following the procedure described in the previous section (IS , Table 19, 40.2; IS : IS ). Wall Pier Shear Design 2-25

48 Shear Wall Design IS 456:2000 and IS 13920:1993 Calculate the absolute maximum permissible nominal shear stress, τ c,max, following the procedure described in the previous section (IS , Table 20, IS ). Compute the horizontal shear reinforcement as follows: If τ v < τ cd, provide minimum links defined by the minimum horizontal shear rebar in accordance with code (IS 32.5; IS , 9.14), else if τ cd < τ v < τ c,max, A s sh v ( τ τ ) v cd tw = (IS 40.4, ; IS ) 0.87 f ys else if τ v > τ c,max, a failure condition is declared. (IS ; IS ) In calculating the horizontal shear reinforcement, a limit is imposed on the f ys as f ys 415 N/mm 2. (IS ; IS 40.4) The minimum ratio of horizontal shear reinforcement to gross concrete area is taken as follows: If there is any load combination involving seismic load present (seismic design), the minimum horizontal shear reinforcing in the wall pier planar leg is taken as A s sh v = t. (IS ) w If there is no load combination involving seismic load present (non-seismic design), the minimum horizontal shear reinforcing in the wall pier planar leg is taken as: 2 A tw if f 415N/mm, sh ys = s 2 v tw if fys > 415N/mm. (IS 32.5.c) 2-26 Wall Pier Shear Design

49 Chapter 2 - Pier Design The maximum of all the calculated A sh /s values, obtained from each design load combination, are reported for the major direction of the wall pier, along with the controlling combination name. The wall pier planar leg shear reinforcement requirements reported by the program are based purely on shear strength consideration. Any other requirements to satisfy spacing considerations or transverse reinforcement volumetric considerations must be investigated independently of the program by the user. Wall Pier Shear Design 2-27

50 Chapter 3 Spandrel Design This chapter describes how the program designs concrete shear wall spandrels for flexure and shear when the "Indian IS " code is selected. The program allows consideration of Rectangular sections and T-beam sections for shear wall spandrels. Note that the program designs spandrels at stations located at the ends of the spandrel. No design is performed at center (midlength) of the spandrel. To compute steel reinforcement at stations located between the two ends, either specify auto mesh options or do a manual meshing of the spandrel and then assign different spandrel labels. The program designs the spandrel for flexure and shear only and reports how much flexural and shear reinforcing is required. The program does not allow reinforcing to be specified or checked. 3.1 Spandrel Flexural Design In this program, wall spandrels are designed for major direction flexure and shear only. Effects caused by any axial forces, minor direction bending, torsion or minor direction shear that may exist in the spandrel must be investigated by the user independent of the program. Spandrel flexural reinforcing is designed for each of the design load combinations. The required area of reinforcing for flexure is calculated and reported at the ends of the spandrel beam. 3-1

51 Shear Wall Design IS 456:2000 and IS 13920:1993 The following steps are involved in designing the flexural reinforcing for a particular wall spandrel section for a particular design loading combination at a particular station. Determine the maximum factored moment M u. Determine the required flexural reinforcing, A s and A s. These steps are described in the following sections Determine the Maximum Factored Moments In the design of flexural reinforcing for spandrels, the factored moments for each design load combination at a particular beam station are obtained first. Then the beam section is designed for the maximum positive and the maximum negative factored moments obtained from all of the design load combinations Determine the Required Flexural Reinforcing In this program, negative beam moments produce top steel. In such cases, the beam is always designed as a rectangular section. In this program, positive beam moments produce bottom steel. In such cases, the beam may be designed as a rectangular section, or as a T-beam section. Indicate that a spandrel is to be designed as a T-beam by specifying the appropriate slab width and depth dimensions, which are provided in the spandrel design overwrites (Appendix B). The flexural design procedure is based on the simplified parabolic stress block, as shown in Figure 3-1 (IS 38.1, Figures 21 and 22). The area of the stress block, C, and the depth of the center of the compressive force from the most compressive fiber, d compression, are taken as C = af ckx u and d compression =βx u (IS 28.1.b) (IS 38.1.c) where x u is the depth of the compression block, and a and β are taken respectively as 3-2 Spandrel Flexural Design

52 Chapter 3 - Spandrel Design a = 0.36, and β = (IS 38.1.c) (IS 38.1.c) a is the reduction factor to account for sustained compression and the partial safety factor for concrete. a is taken as 0.36 for the assumed parabolic stress block (IS 38.1). The β factor establishes the location of the resultant compressive force in concrete in terms of the neutral axis depth. Furthermore, it is assumed that moment redistribution in the member does not exceed the code specified limiting value. The code also places a limit on the neutral axis depth as given below, to safeguard against non-ductile failures (IS 38.1.f). f y x u,max/d The program uses interpolation between the three discrete points given in the code. x u,max d 0.53 if fy 250 fy if 250 < f y = fy if 415 < fy if fy > 500 (IS 38.1.f) The preceding table and the interpolating equation are a manifestation of Clause 38.1(f), which states that the maximum strain in the tension reinforcement in the section at failure should not be less than f y/(1.15e s) (IS 38.1.f). This leads to the following limit: x u,max d = ε ε c,max c,min + ε s,min (IS 38.1.f) Spandrel Flexural Design 3-3

53 Shear Wall Design IS 456:2000 and IS 13920:1993 where ε c,max = fy ε s,min = E s (IS 38.1.b) (IS 38.1.f) If the spandrel satisfies the deep beam criterion, a limit on the depth of the lever arm, z, is enforced based on the assumption that the spandrel is a continuous beam. z max 0.5ls for 0 < ls D< 1 = 0.2( ls + 1.5D) for 1 ls D 2.5 (IS ) The spandrel is considered to be a deep beam if the following condition is satisfied: l D 2.5 (IS 29.1.a) s where D is the total depth of the spandrel and l s is the effective span, which is taken as 1.15 times the clear span (IS 29.2). When the applied moment exceeds the capacity of the beam as a singly reinforced beam, the area of compression reinforcement is calculated on the assumption that the neutral axis depth remains at the maximum permitted value. The maximum fiber compression is taken as ε c,max = (IS 38.1.b) and the modulus of elasticity of steel is taken to be E s = 200,000 N/mm 2. (IS 5.63, 38.1.e, Figure 23) It is assumed that the design ultimate axial force can be neglected. The effect of torsion is neglected. The design procedure used by the program for both rectangular and flanged sections (L-beams and T-beams) is summarized in the sections that follow. 3-4 Spandrel Flexural Design

54 Chapter 3 - Spandrel Design Design for Rectangular Spandrel Beam For rectangular spandrel beams, the limiting depth of neutral axis, x u,max, and the moment capacity as a singly reinforced beam, M single, are obtained first for the section. The reinforcing steel area is determined based on whether M u is greater than, less than, or equal to M single. (See Figure 3-1.) b ε = f ck γ m A s d 0.84 x u x u f s C s 0.42 x u C d T s T c A s ε s Beam Section Strain Diagram Stress Diagram Figure 3-1 Rectangular Spandrel beam design, Positive Moment Calculate the limiting depth of the neutral axis. x u,max d 0.53 if fy 250 fy if 250 < fy = fy if 415 < fy if fy 500 (IS 38.1.f) Calculate the limiting ultimate moment of resistance as a singly reinforced beam. Spandrel Flexural Design 3-5

55 Shear Wall Design IS 456:2000 and IS 13920:1993 M single = αf ckbd x x 1 β d 2 u,max u,max d, where (IS G-1.1.c) α = 0.36, and β = (IS G-1.1.c, 38.1.c) (IS G-1.1.c, 38.1.c) Calculate the depth of neutral axis x u as x u 1 1 4βm =, d 2β where the normalized design moment, m, is given by Mu m = α f bd ck 2. If M u M single the area of tension reinforcement, A s, is obtained from A = M u ( fy γs), z x u z = d 1 β. d where (IS G-1.1) (IS 38.1) If the spandrel is a deep beam, z is limited by the following limit: z z max. (IS ) This is the top steel if the section is under negative moment and the bottom steel if the section is under positive moment. If M u > M single, the area of compression reinforcement, A ' s, is given by Mu M A s = f ( d d ) s single, (IS G-1.2) where d' is the depth of the compression steel from the concrete compression face, and 3-6 Spandrel Flexural Design

56 Chapter 3 - Spandrel Design d f y f s =εc,max Es 1. x u,max γs (IS G-1.2) This is the bottom steel if the section is under negative moment and top steel if the section is under positive moment. From equilibrium, the area of tension reinforcement is calculated as Msingle Mu M A = + s single ( f ) ( )( ) y γs z fy γs d d, where (IS G-1.2) x u,max z = d 1 β. d (IS 38.1) If the spandrel is a deep beam, z is limited by the following limit: z z max. (IS ) A s is to be placed at the bottom and A s is to be placed at the top if M u is positive, and A s is to be placed at the bottom and A s is to be placed at the top if M u is negative Design of Spandrel with T-Beam Section In designing a T-beam spandrel, a simplified stress block, as shown in Figure 3-2, is assumed if the flange is under compression, i.e., if the moment is positive. If the moment is negative, the flange comes under tension, and the flange is ignored. In that case, a simplified stress block similar to that shown in Figure 3-1 is assumed in the compression side Flanged Spandrel Under Negative Moment In designing for a factored negative moment, M u (i.e., designing top steel), the calculation of the steel area is exactly the same as described for a rectangular beam, i.e., no T-beam data is used. The width of the web, b w, is used as the width of the beam. Spandrel Flexural Design 3-7

57 Shear Wall Design IS 456:2000 and IS 13920: Flanged Spandrel Under Positive Moment With the flange in compression, the program analyzes the section by considering alternative locations of the neutral axis. Initially the neutral axis is assumed to be located within the flange. Based on this assumption, the program calculates the depth of the neutral axis. If the stress block does not extend beyond the flange thickness, the section is designed as a rectangular beam of width b f. If the stress block extends beyond the flange, additional calculation is required. See Figure 3-2. b f D f ε = f ck γ m 0.67 f cu γ m A s x u d f s C s 0.42 x u C C f d C w A s ε s T s T w T f b w Beam Section Strain Diagram Stress Diagram Figure 3-2 Design of Wall Spandrel with a T-Beam Section, Positive Moment Assuming the neutral axis to lie in the flange, calculate the depth of neutral axis, x u, as x u 1 1 4βm =, d 2β where the normalized design moment, m, is given by Mu m = α f bd ck f Spandrel Flexural Design

58 Chapter 3 - Spandrel Design x If u D f, the neutral axis lies within the flange. The subsequent calculations for A s are exactly the same as previously defined for the Rectangu- d d lar section design (IS G-2.1). However, in this case, the width of the compression flange, b f, is taken as the width of the beam, b. Compression reinforcement is required when M u > M single. x If u D f >, the neutral axis lies below the flange. Then calculation for d d A s has two parts. The first part is for balancing the compressive force from the flange, C f, and the second part is for balancing the compressive force from the web, C w, as shown in Figure 3-2. Calculate the ultimate resistance moment of the flange as M f = 0.45 f ck (b f b w)y f (d 0.5 y f), (IS G-2.2) where y f is taken as follows: y f Df if Df 0.2 d, = 0.15xu Df if Df > 0.2 d. (IS G-2.2) Calculate the moment taken by the web as M w = M u M f. Calculate the limiting ultimate moment resistance of the web for tension reinforcement only. M w,single = αf ckb wd x x 1 β d 2 u,max u,max d where (IS G-1.1) Spandrel Flexural Design 3-9

59 Shear Wall Design IS 456:2000 and IS 13920:1993 x u,max d 0.53 if fy 250 fy if 250 < f y = fy if 415 < fy if fy > 500 (IS 38.1.f) α = 0.36, and β = (IS G-1.1.c, 38.1.c) (IS G-1.1.c, 38.1.c) If M w M w,single, the spandrel is designed as a singly reinforced concrete beam. The area of steel is calculated as the sum of two parts: one to balance compression in the flange and one to balance compression in the web. M f M w As = +, f d y f z ( y γs)( 0.5 f ) ( y γs) where x u z = d 1 β. d x u 1 1 4βm =, d 2β and Mw m = α f bd ck w 2. If the spandrel is a deep beam, z is limited by the following limit: z z max (IS 29.2.b) If M w > M w,single, the area of compression reinforcement, A s, is given by M M A s = f ( d d ) w w,single, s 3-10 Spandrel Flexural Design

60 Chapter 3 - Spandrel Design where d' is the depth of the compression steel from the concrete compression face, and d f y f s =εc,max Es 1. x u,max γs (IS G-1.2) From equilibrium, the area of tension reinforcement is calculated as where M M M M A = + + s f w,single w w,single ( f )( 0.5 ) ( ) ( )( ) y γs d yf fy γs z fy γs d d x u,max z = d 1 β. d If the spandrel is a deep beam, z is limited by the following limit:, z z max. (IS 29.2.b) A s is to be placed at the bottom and A s is to be placed at the top for positive moment. 3.2 Spandrel Shear Design The program allows consideration of Rectangular sections and T-Beam sections for wall spandrels. The shear design for both of these types of spandrel sections is identical. The wall spandrel shear reinforcing is designed for each of the design load combinations. The required area of reinforcing for vertical shear is calculated only at the ends of the spandrel beam. In this program, wall spandrels are designed for major direction flexure and shear forces only. Effects caused by any minor direction bending, torsion or minor direction shear that may exist in the spandrels must be investigated by the user independent of the program. Spandrel Shear Design 3-11

61 Shear Wall Design IS 456:2000 and IS 13920:1993 The assumptions in designing the shear reinforcement are as follows: The spandrel beam sections are considered to be prismatic. The program does not adjust the shear force for non-prismatic spandrel beam (IS ). The effect on the concrete shear capacity of any concentrated or distributed load in the span of the spandrel beam between two walls or columns is ignored. Also, the effect of the direction support on the beams provided by the columns or walls is ignored. All shear reinforcement is assumed to be perpendicular to the longitudinal reinforcement. The effect of axial force is considered (IS ). The effect of torsion is ignored (IS ). The following steps are involved in designing the shear reinforcement for a particular wall spandrel section for a particular design loading combination at a particular station. Determine the factored shear force V u. Determine the shear stress, τ cd, that can be carried by the concrete. Determine the required shear reinforcing, A sv/s v, to carry the balance of the shear force. The following three sections describe in detail the algorithms associated with this process Determine Factored Shear Force In the design of spandrel beam shear reinforcement, the shear forces and axial force for a particular design load combination at a particular beam section are obtained by factoring the associated shear forces and axial force with the corresponding design load combination factors. The section is essentially considered to be prismatic. If the section is nonprismatic and the depth varies with length, the program does not adjust the 3-12 Spandrel Shear Design

62 Chapter 3 - Spandrel Design design shear force as recommended by code (IS ). In that case, the user is expected to check the shear independently of the program. The program ignores any torsion that might be present. If the spandrel encounters any torsion, the program does not adjust the design shear force as recommended by the code (IS ). In that case, the user is expected to check the shear independently of the program Determine Concrete Shear Capacity Given the design set forces P u and V u, the shear force carried by the concrete, V c, is calculated as follows: where, V c = τ cda cv A cv = b wd (IS 40.1) { r,top r,bot} d = min h d, h d. (IS 40.2) τ cd = kδτ c (IS 40.2) P u if Pu > 0, under compression δ= Ag fck 1 if Pu 0, under tension (IS ) k is always taken as 1, and (IS ) τ c is the basic design shear strength for concrete, which is given by IS Table 19. It should be mentioned that the value of γ c has already been incorporated in IS Table 19 (see Note in IS ). The following limitations are enforced in the determination of the design shear strength as is done in Table 19. A s bd f ck 40 N/mm 2 (for calculation purposes only) Spandrel Shear Design 3-13

63 Shear Wall Design IS 456:2000 and IS 13920:1993 The determination of τ c from Table 19 of the code requires two parameters: 100 s A A and fck. If 100 s becomes more than 3.0, τc is bd bd A calculated based on 100 s A = 3.0. If 100 s becomes less than 0.15, bd bd A s τ c is calculated based on 100 = Similarly, if fck is larger than bd 40 N/mm 2, τ c is calculated based on f ck = 40 N/mm 2. However, if f ck is less than 15 N/mm 2, τ c is reduced by a factor of f ck If γ c is chosen to be different from 1.5, τ c is adjusted with a factor of ( ) 1.5 γ. The absolute maximum limit on nominal shear stress, τ c,max c is calculated in accordance with IS Table 20, which is reproduced in the table that follows (IS , Table 20): Maximum Shear Stress, τ c,max (N/mm 2 ) Concrete Grade M15 M20 M25 M30 M35 M40 τ c,max (N/mm 2 ) If f ck is between the limits, linear interpolation is used. 2.5 if fck < 15 fck if 15 fck < 20 5 fck if 20 fck < 25 5 fck 25 τ c,max = if 25 fck < 30 5 fck if 30 fck < 35 5 fck if 35 fck < if fck 40 (IS ) 3-14 Spandrel Shear Design

64 Chapter 3 - Spandrel Design Determine Required Shear Reinforcement Given V u, the required shear reinforcement in the form of stirrups within a spacing, s v, is given for Rectangular or T-beams by the following: Calculate the design nominal shear stress as V bd u τ v = (IS 40.1) where b is the width of the Rectangular beam or the width of the T-beam web, i.e., (b = b w). Calculate the basic permissible nominal shear stress, τ c, and the design permissible nominal shear stress, τ cd, following the procedure described in the previous section (IS , Table 19, 40.2). Calculate the absolute maximum permissible nominal shear stress, τ c,max, following the procedure described in the previous section (IS , Table 20). Compute the shear reinforcement as follows: If τ v τ cd, provide minimum links defined by A s sv v 0.4bw = (IS 40.3, ) 0.87 f ys else if τ cd <τ v τ c, max, provide links given by ( τ τ ) b 0.46 Asv v cd w bw =, (IS 40.4) s 0.87 f 0.87 f v ys ys else if τ v > τ c, max, a failure condition is declared. (IS ) The following additional checks are performed for spandrels involving seismic load or spandrels satisfying the deep beam criterion. Spandrel Shear Design 3-15

65 Shear Wall Design IS 456:2000 and IS 13920:1993 If any load combination involving seismic load is present (seismic design), the minimum areas of vertical and horizontal shear reinforcing in the spandrel are as follows (IS ): A sv/s v = b w (IS ) A sh/s h = b w (IS ) If the spandrel beam satisfies the deep beam criterion, the minimum areas of vertical and horizontal shear reinforcing in the spandrel are as follows (IS 32.5a): A s sv v A s sh h = b (IS 32.5.c) w = b. (IS 32.5.a) w A spandrel beam is considered to be a deep beam if the following condition is satisfied. Lh 2.5. (IS 29.1) The length L is taken as 1.15 times the clear span (IS 29.2). In calculating the shear reinforcement, a limit is imposed on the f ys as f ys 415 N/mm 2. (IS 39.4) The maximum of all of the calculated A sv / s v and A sh / s h values, obtained from each load combination, is reported along with the controlling shear force and associated load combination number. The shear reinforcement requirements displayed by the program are based purely on shear strength considerations. Any minimum stirrup requirements to satisfy spacing and volumetric considerations must be investigated independently of the program by the user Spandrel Shear Design

66 Chapter 3 - Spandrel Design 3.3 Spandrel Diagonal Reinforcement If seismic load is not present, diagonal reinforcement is not required. If seismic load is present, diagonal reinforcement may or may not be required. If or if l D 3, (IS Draft 9.5.1) s ( ) τ > 0.1 f l D, (IS ), v ck s diagonal reinforcement is required. The area of reinforcement to be provided along each diagonal in a diagonally reinforced spandrel beam is computed as follows: A sd Vu = 2 sin α ( f ys λs ) (IS ) where sinα = 2 s l 0.8D + ( 0.8D) 2 where D is the total depth of the spandrel and l s is the length of the spandrel. In the output, the program reports the diagonal shear reinforcing as required or not required (i.e., optional). The diagonal shear reinforcing is reported as required if ls D 3 or if earthquake-induced shear stress exceeds 0.1 l f D. s ck Spandrel Diagonal Reinforcement 3-17

67 Chapter 4 Design Output 4.1 Overview The program has the capacity to create design output in four major ways graphical display, file output, tabular display, and member specific detailed design information. The graphical display includes input and output design information for members visible in the active window; the display can be sent directly to a printer or saved to a file. The file output includes both summary and detail design data that can be saved in plain text formats. The tabular display output includes both summary and detail design data that can be displayed or saved in many formats, including Excel, Access, and plain text. The member specific detailed design information shows the details of the calculation. The following sections describe some of the typical graphical display, file output, tabular display output, and member specific detailed design information. Some of the design information is very specific to the chosen shear wall design code. This manual addresses "Indian IS " design code related output information only. 4-1

68 Shear Wall Design Manual IS 456:2000 and IS 13920: Display Design Information on the Model The graphical display of design output includes input and output design information for all shear wall members that are visible in the active window. The graphical output can be produced in color or in gray-scaled screen display. The active screen display can be sent directly to the printer or saved to a file in several formats. The on-screen display data is organized into two main groups, as follows. Design Input Material Pier Section Information Design Output Simplified pier longitudinal reinforcing Simplified pier edge members Section Designer pier reinforcing ratios Section Designer pier D/C ratios Spandrel longitudinal reinforcing Shear reinforcing Pier demand/capacity ratios Pier boundary zones Pier longitudinal reinforcing Pier reinforcing ratios Pier D/C ratios Simple pier edge members Pier bounding zones Pier/spandrel shear reinforcing Spandrel diagonal reinforcing Identify failures Note that only one of the listed items can be displayed on the model at a time. Use the Design menu > Shear Wall Design > Display Design Info command to plot design input and output values directly on the model. The Display Design Results form shown in Figures 4-1 and 4-2 will display. Choose the Design Output or Design Input option. One item can be selected from the dropdown list at a time. Click the OK button to display the selected information in the active window. A typical graphical display of longitudinal reinforcing is shown in Figure Display Design Information on the Model

69 Chapter 4 - Design Output Figure 4-1 Choice of design input data for display on the model in the active window Figure 4-2 Choice of design output data for display on the model in the active window Figure 4-3 A typical graphical display Display Design Information on the Model 4-3

70 Shear Wall Design Manual IS 456:2000 and IS 13920:1993 The output shown directly on piers is plotted along an invisible line that extends from the centroid of the pier section at the bottom of the pier to the centroid of the pier section at the top of the pier. Similarly, the output shown directly on spandrels is plotted along an invisible line that extends from the centroid of the spandrel section at the left end of the spandrel to the centroid of the spandrel section at the top of the spandrel. The standard view transformations are available for all shear wall design information displays. Several buttons on the toolbar can be used to switch between 3D and 2D views. Alternatively, click the View menu and the Set 3D View or Set 2D View commands. The onscreen graphical display can be sent to printer using any of the following commands. Use the File menu > Print Graphics command to print the active window. To capture the graphical display in a file for printing through another application, use the File menu > Capture Enhanced Metafile command to create an.emf file, or use the File menu > Capture Picture command to create a bitmap (.bmp) file. Create a screen capture of the active window using the Alt+ Print Screen keyboard keys or create a screen capture of the entire window using the Ctrl + Print Screen keyboard keys. Then use the Ctrl+V keyboard keys to paste the saved image into Paint or other graphical program. By default the graphical displays are in color. It may be advantageous to view or present the display in gray-scale graphics or using a white background. Use the Options menu > Color command to set these options. 4.3 Display Design Information in Tables In addition to model definition and analysis results, the design information for all piers and spandrels or for only selected piers and spandrels can be displayed in tabular spreadsheet format. Currently, the program generates design pier location data, pier basic overwrite data, uniform reinforcing sections, general reinforcing sections, simplified T and C sections, spandrel location data, spandrel basic overwrite data, and spandrel geometry data. The tabular spreadsheet output can be displayed by selecting the Display menu > Show Tables command to access the Choose Tables for Display form, an example of which is shown in Figure 4-4. That form can be used to choose which tables or sets of tables are to be displayed. 4-4 Display Design Information in Tables

71 Chapter 4 - Design Output Figure 4-4 Choice of design data tables for tabular display The names of the tables are displayed in a tree structure, which can be collapsed or expanded by clicking on an item in the tree. Click on the small check boxes preceding the items to select those tables for display. If a branch of the tree is selected, all of the tables under that branch are selected. The selected set of tables can be saved as a Named Set using the Save Named Set button. This named set can be used in the future for quick selection. If one or more frame members were selected on the structural model before accessing the Choose Tables for Display form, the Selection Only check box will be checked when the form displays and, the program will display information for the selected members only; uncheck the check box to display information for all applicable "unselected" members in the model. Use the other buttons on the form to tailor the data display. For example, click the Select Load Cases button to specify which load cases are to be included in Display Design Information in Tables 4-5

72 Shear Wall Design Manual IS 456:2000 and IS 13920:1993 the display of model definition data; click the Select Analysis Case and Modify/Show Options to specify which analysis cases are to be included and how analysis results are to be displayed. After selecting all of the tables for shear wall design and the display options, click the OK button to display a form showing one of the selected design tables, with a drop-down list in the upper right-hand corner of the form that can be used to select other tables for display. A typical design table in shown in Figure 4-5. Figure 4-5 A typical tabular display of design data. Use the scroll bars on the bottom and right side of the tables to scroll right and left or up and down if portions of the data table can not be displayed in the form's display area. The columns can be resized by clicking the left mouse button on the separator of the headers, holding down the left mouse button and then dragging the mouse to the left or right. Reset the column widths to their default values by selecting the View menu > Reset Default Column Widths command on the form. The table can be split into two or more tables by clicking on the small black rectangular area near the bottom-left corner of the table, holding down the left mouse button, and then dragging the mouse button to the 4-6 Display Design Information in Tables

73 Chapter 4 - Design Output left or right. Repeat this process to add more splits. Use the split and horizontal scroll bar to put two columns side by side for easier comparison. The splits can be removed by selecting the View menu > Remove Splits command on the form. Alternatively, remove the split by clicking, holding and dragging the left mouse button to merge the split key to its original location. Select multiple consecutive columns by putting the cursor on the header, holding down the mouse button, and then dragging the mouse button left or right. Alternatively, depress the Shift key and click the left mouse button to select a range of columns. Each of the individual fields (columns) can be formatted. Fields with text information can be set for specific types of alignment (center, left, right) and to specific widths. The current table (i.e., the table in the active window) can be exported to the Windows Clipboard. Many other features of the design tables are left for the user to discover by using the program. 4.4 Display Detailed Member Specific Information The program has the capability to display shear wall design details for specific piers or spandrels. When the design results are displayed on the model in the active window, the detailed design information can be accessed by right clicking on the desired frame member to display the detailed design output. If the design result is not displayed, click the Design menu > Shear Wall Design > Interactive Wall Design command and then right click on the frame member. An example of that form is shown in Figure 4-6. The Overwrites and Combos buttons allow the user to access the interactive mode for design. For both piers and spandrels, the program reports the spandrel or pier identification by Story ID and Pier ID or Spandrel ID, and the pier/spandrel midpoint location. Additional information reported depends on the type of member. For spandrels, the program reports the detailed flexural and shear design information for the two ends of the spandrel. The program also reports the envelope information for the design rebar for flexure and shear with the associated load combination names, design forces, and some intermediate data. In addition, the program reports diagonal rebar design envelope data. Display Detailed Member Specific Information 4-7

74 Shear Wall Design Manual IS 456:2000 and IS 13920:1993 Figure 4-6 A typical member specific shear wall design information summary For piers, the program reports the detailed P-M-M flexural design information, the detailed shear design information, and boundary element check information. The P-M-M flexural design/check information is reported for the overall design/check section. If the section is a Uniformly Reinforced pier section or a General Reinforcing pier section (SD Section), and designated as a Design problem, the program reports rebar area, or if it is designated as a Check problem, the program reports the D/C ratio. Simplified T and C sections are always considered to be design sections. Shear design information is computed for each planar leg and only the most critical leg is reported. A boundary check also is performed for each planar leg and only the most critical leg is reported. All information is reported at two sections: top and bottom of the story. The program reports the envelope information for P-M-M flexural rebar and D/C ratio, shear rebar, and boundary check with associated load combination names, the design forces, and some intermediate data. For information about all other legs, the user should look into Tabular Display Design Information (the 4-8 Display Detailed Member Specific Information

75 Chapter 4 - Design Output previous section) or Tabular Text Output of Design Information (the next section). The design detailed information is always reported for the design sections. The forces are always calculated based on analysis section. For spandrels, the design section is always the same as the analysis section. For piers, the design sections can differ from the analysis section, especially if the pier section is a General Reinforcing section (SD Section) or a Simplified T and C section. See Appendix E for details. The design sections for piers are used only for P-M-M flexural rebar design or check. However for shear design and bounding element checks, the program identifies individual planar legs of the analysis section and design/check is based on the individual legs of the analysis section. The detailed design information window provides an Overwrites button and a Combos button near the bottom of the window. The Overwrites button can be used to access the Pier/Spandrel Design Overwrites form, which allows the user to edit the overwrites. An example of the form is shown in Figure 4-7. The Combos button can be used to access the Design Load Combinations Selection form, which allows the user to modify the selection of load combinations for design. An example of the form is shown in Figure 4.8. Figure 4-7 A typical Overwrites form Display Detailed Member Specific Information 4-9

76 Shear Wall Design Manual IS 456:2000 and IS 13920:1993 Figure 4-8 A typical Design Load Combination Selection form Interactive Shear Wall Design Interactive design is a powerful mode that allows quick, on-screen review of design results for a specific pier or spandrel. This mode allows easy modification to design parameters (overwrites) and design load combinations, and immediate review of the new results. Note that a design must have been run for the interactive design mode to be available. To run a design, click the Design menu > Shear Wall Design > Start Design/Check of Structure command. To enter the interactive design and review mode, right click on a wall pier or spandrel while the design results are displayed. If design results are not currently displayed (and the design has been run), click the Design menu > Shear Wall Design > Interactive Wall Design command and then right click a pier or spandrel to enter the interactive design and review mode for that pier or spandrel. Note that if both a pier and a spandrel label are assigned to the right-clicked object, a pop-up box offers the choice to enter the interactive design and review mode for the pier or for the spandrel. Appendix D provides additional information about interactive shear wall design Display Detailed Member Specific Information