Chapter 4 Ductile Coupled Reinforced Concrete Shear Walls

3/30/22Chapter 4 Ductile CoupledReinforced Concrete Shear Walls2020 NEHRP Provisions Training MaterialsS. K. Ghosh and Prabuddha Dasgupta, S. K. Ghosh Associates LLCBSSC1Coupled WallsMLMRVLVRLATERAL LOADVCOUPLING BEAM,TYPICALM1WALL PIER,TYPICALM2LTC221

3/30/22Coupled WallsCourtesy: CaryKopczynski & Company,Bellevue, WA33Coupled WallsCourtesy: MagnussonKlemencic Associates,Seattle, WA42

3/30/22Coupled WallsCourtesy: CaryKopczynski & Company,Bellevue, WA55Coupled Walls663

3/30/22Coupled WallsCoupled shear wall systems are recognized as distinct fromisolated shear wall systems in Canadian and New Zealand codes;they are also accorded higher response modification factors inview of their superior seismic performance. ASCE/SEI 7, prior toits 2022 edition, made no such distinction.77Ductile Coupled Shear WallsBertero wrote in 1977: “Use of coupled walls in seismic-resistantdesign seems to have great potential. To realize this potential it wouldbe necessary to prove that it is possible to design and construct“ductile coupling girders” and “ductile walls” that can SUPPLY therequired strength, stiffness, and stability and dissipate significantamounts of energy through stable hysteretic behavior of their criticalregions.”Thus, discussion needs to focus not on just coupled walls, but ductilecoupled walls consisting of ductile shear walls and ductile couplingbeams.884

3/30/22Energy Dissipation in Coupling BeamsMKA Study:Non-linear response history analyses were conducted usingspectrally matched ground motion records on a variety of coupledshear wall archetypes. Archetypes ranged from 5 to 50 stories inheight and contained a range of longitudinal reinforcement ratiosin the coupling beams as well as the shear walls.99Energy Dissipation in Coupling BeamsCourtesy: MagnussonKlemencic Associates10105

3/30/22ACI 318-19 18.10.9 Ductile Coupled Walls18.10.9.1 Ductile coupled walls shall satisfy the requirements ofthis section.18.10.9.2 Individual walls shall satisfy hwcs/ℓw 2 and theapplicable provisions of 18.10 for special structural walls.18.10.9.3 Coupling beams shall satisfy 18.10.7 [Coupling beams]and (a) through (c) in the direction considered.(a) Coupling beams shall have ℓn/h 2 at all levels of the building.(b) All coupling beams at a floor level shall have ℓn/h 5 in at least90 percent of the levels of the building.(c) The requirements of 18.10.2.5 shall be satisfied at both ends ofcoupling beams [reinforcement developed for 1.25fy].1111Special Shear Walls12126

3/30/22Ductile Coupling Beams§ Aspect ratio ln/h 4Satisfy requirements of 18.6§ Aspect ratio ln/h 4 Permitted to be reinforced with two intersecting groups ofdiagonal bars§ Aspect ratio ln/h 2 and Vu 4 f cAcw Must be reinforced with two intersecting groups of diagonalbars1313Ductile Coupling BeamsSource: http://nees.seas.ucla.edu/pankow14147

3/30/22Ductile Coupling BeamsSource: http://nees.seas.ucla.edu/pankow15152020 NEHRP Provisions16168

3/30/222020 NEHRP Provisions§ Part 1: Modifications to ASCE/SEI 7-16§ Part 2: Commentary to the Modifications§ Part 3: Resource Papers1717BSSC PUC Issue Team 4§§§§§§§Richard Bennett, University of Tennessee, Knoxville, TNMichel Bruneau, University of Buffalo, Buffalo, NYKelly Cobeen, Wiss, Janney, Elstner, Emeryville, CADavid Fields, Magnusson Klemencic, Seattle, WAS. K. Ghosh, S. K. Ghosh Associates, Palatine, IL (Chair)Gino Kurama, University of Notre Dame, Notre Dame, INAndy Taylor, KPFF, Seattle, WA189

3/30/22BSSC PUC Issue Team 4Jeffrey W. Berman, University of Washington, Seattle, WALarry Fahnestock, University of Illinois, Urbana-Champaign, ILJoe Ferzli, Cary Kopczynski & Company, Bellevue, WAJohn Hooper, Magnusson Klemencic, Seattle, WADawn Lehman, University of Washington, Seattle, WAPhil Line, American Wood Council, Washington, D.C.Laura Lowes, University of Washington, Seattle, WARafael Sabelli, Walter P. Moore, San Francisco, CAJohn Wallace, University of California, Los Angeles, CAAmit Varma, Purdue University, West Lafayette, INJon-Paul Cardin, American Institute of Steel Construction, Coeur d’Alene, ID19P695 Study202010

3/30/22P-695 StudyForty-one ductile coupled shear wall buildings were designedusing a range of variables expected to influence the collapsemargin ratio; the primary variables were building height (i.e., 6, 8,12, 18, 24, and 30 stories), wall cross section (i.e., planar andflanged walls), coupling beam aspect ratio (ℓ! /ℎ) ranging from2.0 to 5.0, and coupling beam reinforcement arrangement (i.e.,diagonally and conventionally reinforced).21P-695 Study – Plan Views of Archetype Buildings2211

3/30/22P-695 Study – Elevation View of Archetype Buildings23P-695 Study – Design ParametersThe designs were for Risk Category II structures with an importancefactor 𝐼! 1.0. It incorporated provisions of ASCE/SEI 7-16 and ACI318-19 as well as the seismic design parameters specified in FEMAP695 (importance factor, redundancy factor, and site class and spectralvalues). The redundancy factor ρ was taken equal to 1.0. The seismicspectral acceleration values used are summarized below for seismichazard Dmax as specified in FEMA P695.§SS 1.5g§S1 0.6gFa 1.0Fv 1.5SDS 1.00 gSD1 0.60g2412

3/30/22Additional ACI 318-19 Changes in Special Shear Wall DesignThere have been four significant ACI 318-19 code changes, alladopted in our FEMA P695 study, to address the flexuralcompression wall failure issue.(1) 18.10.3.1 (shear amplification) - would typically require designshear (required shear strength) Vu to be amplified by a factor ofup to 3 (similar to New Zealand, Canada).25Additional ACI 318-19 Changes in Special Shear Wall Design(2) 18.10.6.4 - requires improved wall boundary and wall webdetailing, i.e, overlapping hoops if the boundary zone dimensionsexceed 2:1, crossties with 135-135 hooks on both ends, and 135135 crossties on web vertical bars.(3) 18.10.6.2(b) (Wall drift or deformation capacity check) requires a low probability of lateral strength loss at MCE levelhazard (you can think of it as requiring a minimum wallcompression zone thickness), and2613

3/30/22Additional ACI 318-19 Changes in Special Shear Wall Design(4) 18.10.2.4 - Minimum wall boundary longitudinal reinforcement,to limit the potential of brittle tension failures for walls that arelightly-reinforced.27Shear Amplification: Concrete Shear Walls282814

3/30/22Shear Amplification: Concrete Shear Walls2929Shear Amplification: Concrete Shear Walls303015

3/30/22Earthquake Force-Resisting Structural Systems of Concrete —ASCE/SEI 7-22DetailingReferenceSectionR1. Special reinforced concreteshear walls14.2521/22. Ductile Coupled reinforcedconcrete shear wallsq14.283. Ordinary reinforced concreteshear walls14.24Basic Seismic Force-resistingSystemΩ0CdSystem Limitations And Building HeightLimitations (Ft) By Seismic Design NLNLNPNPNPA. Bearing Wall SystemqStructural height, hn, shall not be less than 60 ft (18.3 m).Minimum height is intended to ensure adequate degree of coupling and significant energy dissipation provided bythe coupling beams.3131Earthquake Force-Resisting Structural Systems of Concrete —ASCE/SEI 7-22DetailingReferenceSectionR4. Special reinforced concreteshear walls14.2621/25. Ductile Coupled reinforcedconcrete shear wallsq14.286. Ordinary reinforced concreteshear walls14.25Basic Seismic Force-resistingSystemΩ0CdSystem Limitations And Building HeightLimitations (Ft) By Seismic Design 1/2NLNLNPNPNPB. Building Frame SystemqStructural height, hn, shall not be less than 60 ft (18.3 m).323216

3/30/22Earthquake Force-Resisting Structural Systems of Concrete —ASCE/SEI 7-22Basic Seismic 0CdSystem Limitations And Building HeightLimitations (Ft) By Seismic Design CategoryBCDEFD. Dual Systems with Special Moment Frames3. Special reinforced concreteshear walls14.2721/251/2NLNLNLNLNL4. Ductile Coupled reinforcedconcrete shear wallsq14.2821/28NLNLNLNLNL5. Ordinary reinforced concreteshear walls14.2621/25NLNLNPNPNPqStructural height, hn, shall not be less than 60 ft (18.3 m).3333FEMA Publication3417

3/30/22Example ProblemDesign of a Special ReinforcedConcrete Ductile Coupled WallFederal Emergency Management Agency353535IntroductionA 22-story reinforced concrete residential building is designedfollowing the requirements of ASCE/SEI 7-22, and ACI 318-19.The building consists of a flat plate-column gravity system with acentral core, formed by four reinforced concrete coupled structuralwalls, which acts as the seismic force-resisting system. Thestructural walls are designed as Ductile Coupled ReinforcedConcrete Shear (Structural) Walls.A computer rendering of the building framing is shown on the nexttwo slides. The plan view of the building changes from one floor toanother. A plan view of the second floor of the building is shown.363618

3/30/22Example Building Configuration3D View37Example Building ConfigurationSecond Floor Plan View383819

3/30/22Design Criteria§ Member Sizes: Shear walls: 26 in. thickSlabs (2nd and 3rd floors): 8 in. thick(4th floor and higher): 7.5 in. thickGravity columns: Various sizes§ Material properties: Concrete (used in structural walls and columns): fc’ 8000 psi (all floors) Concrete (used in slabs): fc’ 6000 psi (floors) All members are constructed of normal weight concrete (wc 150 pcf) Reinforcement (used in all structural members): fy 60,000 psi3939Design Criteria§ Service Loads: Superimposed dead load: 25 psf (includes SDL on the floor plus theweight of cladding distributed over the floor slab.) Live load: Based on the 40 psf live load prescribed in ASCE/SEI 7-22Table 4.3-1 for residential buildings (private rooms and corridors servingthem), a reduced live load of 20 psf is used in the example. Reduced roof Live load: 20 psf§ Seismic Design Data: Risk Category: II Seismic importance factor, Ie 1.0 Site Class: D404020

3/30/22Design Criteria§ Seismic Design Data (contd.): The maximum considered earthquake spectral response acceleration:At short periods, SS 1.65g, andAt 1-sec period, S1 0.65g.The maximum considered earthquake spectral response acceleration(site modified):At short periods, SMS 1.65g, andAt 1-sec period, SM1 0.98g.Design Spectral Response Acceleration Parameters (at 5% damping):At short periods: SDS 2/3 SMS /g 2/3 1.65 1.10At 1-sec period: SD1 2/3 SM1 /g 2/3 0.98 0.654141Design Criteria§ Seismic Design Data (contd.): Long-period transition period, TL 8 secDuctile Coupled Reinforced Concrete Structural Walls . R 8; Cd 8.0,Ω0 2.5(ASCE/SEI 7-22 Table 12.2-1)Seismic Design Category: Based on both SDS (ASCE/SEI 7-22 Table11.6-1) and SD1 (ASCE/SEI 7-22 Table 11.6-2), the Seismic DesignCategory (SDC) for the example building is D.424221

3/30/22Design ProcedureAlthough ASCE/SEI 7-22 permits the Equivalent Lateral Forceprocedure to be used in all situations, the modal responsespectrum analysis (MRSA) procedure (ASCE/SEI 7-22 Section12.9.1) is used in this example. However, as part of the MRSAprocedure, base shear is also determined using Equivalent LateralForce (ELF) procedure. This is because ASCE/SEI 7-22 requiresthat the base shear obtained from MRSA be scaled up to matchthe ELF base shear.The building was modeled in ETABS 2016, and the total seismicweight was obtained from the program as 43,099 kips.4343Modal Response Spectrum AnalysisA 3-D modal response spectrum analysis (MRSA) is performed using ETABS(v2016).§ Semi-rigid diaphragms are assigned at each level.§ The effective cracked member stiffnesses used in the analyses are asfollows: Columns and shear walls, Ieff 0.7Ig Coupling beams, Ieff 0.25Ig Gravity columns, Ieff 0.1Ig (with pinned connections at the base)§ Adequate number of modes are considered in the modal analysis toincorporate 100% of the modal mass in each of x- and y-directions. Also,appropriate scale factors are applied to the base shears calculated in the xand y-directions to amplify them to those calculated in the ELF procedure.444422