Shear wall Prof Schierle 1Shear wallNarrow wallsmay overturnShear wall Prof Schierle 2Shear walls• Resist lateral load in shear• Resist load only parallel to wall1 Wood studs with plywood2 Metal studs with plywood3 Reinforced Concrete wall4 Reinforced CMU wall5 Un-reinforced brick wall(not allowed in seismic areas)6 Reinforced 2-wythe brick wall7 Party walls - double studs for 65 STC (STC = Sound Transmission Coefficient)Shear wall Prof Schierle 31 X-direction concentric, Y-direction eccentric2 X-direction eccentric, Y-direction eccentric3 X-direction concentric, Y-direction concentric4 X-direction concentric, Y-direction concentric5 X-direction concentric, Y-direction concentric6 X-direction concentric, Y-direction concentricNote: 5 is better than 6 to resist torsionConcentric & eccentric shear wallsNote: eccentric shear walls cause torsion and should be avoidedShear wall vs. lateral resistanceNote: shear walls resist lateral load only parallel to wall1 Shear walls resist only lateral load parallel to wall2 One-way shear walls collapse @ perpendicular load3 Eccentric shear walls cause torsion4 Concentric shear walls resist torsionNote: Walls in 4 are offset but provide concentric supportShear wall Prof Schierle 4tPlywood Shear WallPlywood must be nailed to wood framing to resist lateralshear of wind and seismic forces.1 Plywood shear wall 2 Plywood shear wall with joint3 Max. shear wall aspect ratio 1:3.5(Los Angeles 1:2)4 Plywood nail spacingA Blocking to transfer shearBNailC Plywood sheathingD Hold-down (essential for short walls)E Nail spacing at panel edges (max. 5)F Nail spacing at other studs (max. 12”)Shear wall Prof Schierle 5Four Town Homes, Beverly Hills• Four two-story units over concrete garage • 12” concrete slab on columns at 30’x30’ provides 3-hour fireseparation between garage and residential units above• Concrete slab designed for of 300 psf allows wood framinganywhere regardless of column locations• Double stud party walls for 65 STC sound rating(STC = Sound Transmission Coefficient = sound rating)Shear wall Prof Schierle 6Rear FrontShear wall Prof Schierle 7Limitations of:• Height H• Floor Area AShear wall Prof Schierle 8Terrace Housing Hermosa BeachThe project size required separation by 2-hr fire walls to comply with area limitsShear wall Prof Schierle 9 Terrace Homes Hermosa BeachDesign concept: to minimized grading and retaining walls: adapt building to site instead of adapting site to buildingA 14 x 22 ft module allows shear walls aligned verticallyEach two-story unit has two terraces for outdoor livingTerraces provide open space that allowed 33 units ata lot zoned for only 25 units by conventional planningRaised rear provides energy-saving cross ventilationShear wall Prof Schierle 10Height limit 3-story from gradeRaised rear provides cross ventilationSlanted party walls screen ocean clareSun shades, planters, and party walls provide privacy Length shear wallsWidth shear wallsCommunity space Terracing provides Residential scaleShear wall Prof Schierle 11Terrace Housing Taipei, ChinaArchitect: G G SchierleEngineer: China Sincere200 housing unitsCombined shear wall & concrete frame:• Shear walls provide stiffness• Concrete frames provide ductilityfor seismic safetyShear wall Prof Schierle 12Shear wall Prof Schierle 13Reinforced brick masonryCMU walls (Concrete Masonry Units)Shear wall Prof Schierle 14Reinforced concrete wallReinforced CMU wallShear wall Prof Schierle 15Masonry shear reinforcing1 Wall reinforcing for seismic areas2 Max. bar spacing for required cross-sectionareas (0.1% of wall cross-section area)A Vertical bars(max. 4 ft or 6 x wall thicknessB Horizontal bars (max. 4 ft in seismic areas) C Bars around wall openings, extending min. 24”or 40 bar diameters beyond openingD Horizontal bars @ wall base and topE Bars at structural floors and roofF Spacing of bar sizes # 3 to # 7G Wall thicknessRebar diameter Cross-sectionBar # (in) (in2)#3 3/8 0.11#4 4/8 0.20#5 5/8 0.31#6 6/8 0.44#7 7/8 0.60Shear wall Prof Schierle 16Horizontal Diaphragmstransfer lateral load to shear walls andother elements two ways 1 Flexible diaphragm (wood)transfers in proportion to tributary area.Wall reactions are: R = w (tributary area supported by wall)w = uniform load 2 Rigid diaphragm (concrete & steel)transfers in proportion to wall stiffness.Reactions for walls of equal material:R1 = WL13/ L3 (L3 = L13+L23+L33)R2 = WL23/ L3 R3 = WL33/ L3whereL = Lengths of wallsW = Total load supported by all wallsShear wall Prof Schierle 17Flexible diaphragm / plywood wallsAssume: DL= 24 psf, Seismic factor CS= 0.15Flexible floor and roof diaphragms transfer loads proportional to thetributary area supported by walls. This may be computed as follows: • Unit shear = shear per level / floor area per level • Shear per wall = unit shear x tributary area supported by wall• Shear per foot = shear per wall / wall lengthDead loadDL per level: W = 24 psf x 68’ x 150’/ 1000 W = 235 kDL at 3 Levels: 3 x 235 k W = 705 kBase shearV= CSW = 0.15 x705 V = 106 kArea per level A= 68 x 150 A = 10,200 ft2Shear per square foot per levelv0 = V0/A = 106 k x 1000 / 10200 v0 = 10.4 psfv1 = V1/A = 88 k x 1000 / 10200 v1 = 8.6 psfv2 = V2/A = 53 k x 1000 / 10200 v2 = 5.2 psfVertical force distributionFx= V wx hx /  (wi hi)Level wx hx= wx hxLevel 2: 235 k x 27’ = 6345 k’Level 1: 235 k x 18’ = 4230 k’Level 0: 235 k x 9’ = 2115 k’  wihI = 12690 k’/ (wi hi) V = FxVx =  Fx0.50 x 106 = 53 k V2= 53 k 0.33 x 106 = 35 k + 53 V1= 88 k0.17 x 106 = 18 k + 88 V0 = 106 k V = 106 k0.50 = 6345 / 126900.33 = 4230 / 126900.17 = 2115 / 12690Shear wall Prof Schierle 18Wall design (Use Structural I plywood)Level 0 (v0 = 10.4 psf) Wall A = 10.4 psf (15’) 30’/12’= 390 plf use 5/16, 6d @ 3” = 390 plfWall B = 10.4 psf (19’) 30’/24’= 247 plf use 7/16, 8d @ 6” = 255 plfWall C = 10.4 psf (34’) 15’/30’= 177 plf use 5/16, 6d @ 6” = 200 plfLevel 1 (v1 = 8.6 psf)Wall A = 8.6 psf (15’) 30’/12’= 323 plf use 15/32, 10d@6”= 340 plfWall B = 8.6 psf (19’) 30’/24’= 204 plf use 3/8, 8d @ 6” =