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Shea hearr wall wallss • • 1 2 3 4 5 6 7
Resist lateral load in shear Resis istt loa load only paralle llell to wall Wood stu tud ds with ply lyw wood Meta tall stu stud ds wit ith h ply lyw wood Rein info forc rce ed Concre rete te wall Rein info forrced CMU wall Un-rein info forrced bric ick k wall (not allowed in seismic areas) Rein info forc rce ed 2-w -wy yth the e bric rick k wall Part rty y walls - double stu tud ds fo forr 65 65 STC (STC = Sound Transmission Coefficient)
Shea hearr wall wallss • • 1 2 3 4 5 6 7
Resist lateral load in shear Resis istt loa load only paralle llell to wall Wood stu tud ds with ply lyw wood Meta tall stu stud ds wit ith h ply lyw wood Rein info forc rce ed Concre rete te wall Rein info forrced CMU wall Un-rein info forrced bric ick k wall (not allowed in seismic areas) Rein info forc rce ed 2-w -wy yth the e bric rick k wall Part rty y walls - double stu tud ds fo forr 65 65 STC (STC = Sound Transmission Coefficient)
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Shear wa walls re res sis istt on only la late tera rall loa load para ralle llell to wall One-w -wa ay sh shear wa walls co colla llap pse @perp rpe endic icu ula larr loa load Eccentr tric ic shear wa walllls s cause to torrsio ion n Concentr tric ic shear walls resis istt to torrsio ion n
d e d i o v a e b d l u o h s d n a n o i s r o t e s u a c s l l a w r a e h s c i r t n e 1 c c 2 e 3 : e 4 t
X-direction concentric, Y-directi -direction on eccentric X-d -dir ire ectio tion n eccentr tric ic,, Y-d -dir ire ectio tion n eccentr tric ic X-d -dir ire ectio tion n co concentr tric ic,, Y-d Y-dir ire ectio tion n co concentr tric ic X-d -dir ire ectio tion n co concentr tric ic,, Y-d Y-dir ire ectio tion n co concentr tric ic
Plywood Shear Wall Plywood must be nailed to wood framing to resist lateral shear of wind and seismic forces.
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Plywood shear wall Plywood shear wall with joint Max. shear wall aspect ratio 1:3.5 (Los Angeles 1:2) Plywood nail spacing
A B C D E F
Blocking to transfer shear Nail Plywood sheathing Hold-down (essential for short walls) Nail spacing at panel edges (max. 5) Nail spacing at other studs (max. 12” )
Four Town Homes, Beverly Hills ••
Four two-story units over concrete garage 12” concrete slab on columns at 30’x30’ provides 3-hour fire separation between garage and residential units above • Concrete slab designed for of 300 psf allows wood framing anywhere regardless of column locations • Double stud party w alls for 65 STC sound rating (STC = Sound Transmission Coefficient = sound rating)
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Limitations of: • Height H • Floor Area A
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Terrace Homes Hermosa Beach Design concept: to minimized grading and retaining walls: adapt building to site instead of adapting site to building
A 14 x 22 ft module allows shear walls aligned vertically Each two-story unit has two terraces for outdoor living Terraces provide open space that allowed 33 units at a lot zoned for only 25 units by conventional planning Raised rear provides energy-saving cross ventilation
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Height limit 3-story from grade Length shear walls Width shear walls
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Terrace Housing Taipei, China Architect: G G Schierle Engineer: China Sincere
200 housing units Combined shear wall & concrete frame: • Shear walls provide stiffness • Concrete frames prov ide ductility for seismic safety
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Masonry shear reinforcing 1 2
Wall reinforcing for seismic areas Max. bar spacing for required cross-section areas (0.1% of wall cross-section area)
A Vertical bars (max. 4 ft or 6 x wall thickness B Horizontal bars (max. 4 ft in seismic areas) C Bars around wall openings, extending min. 24” or 40 bar diameters beyond opening D Horizontal bars @ wall base and top E Bars at structural floors and roof F Spacing of bar sizes # 3 to # 7 G Wall thickness Rebar Bar # #3 #4 #5 #6
diameter (in) 3/8 4/8 5/8 6/8
Cross-section (in 2) 0.11 0.20 0.31 0 44
Horizontal Diaphragms transfer lateral load to shear walls and other 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: (L3 = L13+L23+L33) R1 = WL13 / L3 R2 = WL23 / L3 R3 = WL33 / L3 where L = Lengths of walls
Flexible diaphragm / plywood walls Assu me: DL= 24 psf, Seismic factor CS = 0.15 Flexible floor and roof diaphragms tr ansfer l oads proportional to the tribu tary area supported by walls. This may be computed as follows: • Unit shear = shear per level / floo r area per level • Shear per wall = unit shear x trib utary area supported by wall • Shear per foot = shear per wall / wall length Dead load DL per level: W = 24 psf x 68’ x 150’/ 1000 DL at 3 Levels: 3 x 235 k Base shear V= CS W = 0.15 x705
Vertical force distribution Fx = V w x h x / (w i h i ) Level wx h x = w x h x/ Level 2: 235 k x 27’ = 6345 k’ Level 1: 235 k x 18’ = 4230 k’ Level 0: 235 k x 9’ = 2115 k’ w i h I = 12690 k’
W = 235 k W = 705 k V = 106 k
0.50 = 6345 / 12690 0.33 = 4230 / 12690 0.17 = 2115 / 12690 (w i h i ) V = Fx 0.50 x 106 = 53 k 0.33 x 106 = 35 k 0.17 x 106 = 18 k
+ 53 + 88
Vx = Fx V2 = 53 k V1 = 88 k V0 = 106 k V = 106 k
Area per level A= 68 x 150 Shear per square foot per l evel
A = 10,200 ft 2
v 0 = V0/A = 106 k x 1000 / 10200
v 0 = 10.4 psf
Wall design (Use Structural I plywood) Level 0 (v 0 = 10.4 psf) Wall A = 10.4 psf (15’) 30’/12’= 390 plf
use 5/16, 6d @ 3” = 390 plf
Wall B = 10.4 psf (19’) 30’/24’= 247 plf
use 7/16, 8d @ 6” = 255 plf
Wall C = 10.4 psf (34’) 15’/30’= 177 plf
use 5/16, 6d @ 6” = 200 plf
Wall D = 10.4 psf (34’) 30’/30’= 354 plf
use 3/8, 8d @ 4” = 360 plf
Level 1 (v 1 = 8.6 psf) Wall A = 8.6 psf (15’) 30’/12’= 323 plf
use 15/32, 10d@6” = 340 plf
Wall B = 8.6 psf (19’) 30’/24’= 204 plf Wall C = 8.6 psf (34’) 15’/30’= 146 plf
use 3/8, 8d @ 6” = 230 plf use 5/16, 6d @ 6” = 200 plf
Wall D = 8.6 psf (34’) 30’/30’= 292 plf
use 5/16, 6d @ 4” = 300 plf
Level 2 (v 2 = 5.2 psf) Wall A = 5.2 psf (15’) 30’/12’ =195 plf
use 5/16, 6d @ 6” = 200 plf
Wall B = 5.2 psf (19’) 30’/24’ =124 plf
use 5/16, 6d @ 6” = 200 plf
s e p y t l l a w o w t y l n o t c e l e s , y f i l p m i s o t
Rigid diaphragm / masonry shear walls Assume: Seismic factor CS =0.17 Al lo wabl e maso nr y shear stress Structural walls DL Length of walls 12 (30’)+14 (12)+8 (24) DL = (720’) 8’(7.625” /12” ) 120 pcf/[(68) 150] Floor/roof (12” slab) Miscellaneous DL
Fv = 85 ps i L = 720’ DL = 43 psf 150 psf 7 psf DL = 200 psf
Dead l oad DL / level: W = 200 psf x 68’ x 150’/ 1000 DL at 3 Levels: W = 3 x 2040 k
W = 2040 k W = 6120 k
Base shear (CS times 1.5 for ASD masonry shear per IBC 2106.5.1) V=1.5 CS W V = 1.5 x 0.17 W = 0.26 x 6120
V = 1591 k
Vertical force distribution Fx= (V - Ft ) w x h x / (w i h i )
0.50 = 55080 / 110160 0.33 = 36720 / 110160 0.17 = 18360 / 110160
= Fx Level wx h x = w x h x / (w i h i ) V Level 2: 2040 k x 27’ = 55080 k’ 0.50 x 1591 = 796 k Level 1: 2040 k x 18’ = 36720 k’ 0.33 x 1591 = 525 k Level 0: 2040 k x 9’ = 18360 k’ 0.17 x 1591 = 270 k
Vx = Fx 796 k + 796 = 1321 k + 1321 = 1591 k
Rigid diaphragm / masonry shear walls Assume allowable masonry shear stress
Fv = 85 psi
Rigid diaphragms resist lateral load in proporti on to wall stiffn ess. For walls of constant height and material, relative stiffn ess is con stant. In width d irection all walls are equal and, thus, have constant stiffn ess. In length direction relative wall stiffness is:
R = L x3 /
From last slide: Level 2 V2 = 796 k Level 1 V1 = 1321 k Level 0 V0 = 1591 k Base shear V = 1591 k
L i3
B walls R = (12)3 / [(12)3 +(24)3] C walls R = (24)3 / [(12)3 +(24)3]
R= 0.11 R= 0.89
Wall cross section areas: A walls = 12(30’)12” (7.625” ) B wall s = 14(12’)12” (7.625” ) C wall s = 8(24’)12” (7.625” )
A = 32940 in2 B = 15372 in 2 C = 17568 in 2
Level 0 (V0 = 1591 k) Wall A = (1591) 1000 / 32940 Wall B = (1591) 1000 (0.11) / 15372 Wall C = (1591) 1000 (0.89) / 17568
48 psi < 85 19 psi < 85 81 psi < 85
Level 1 (V1 = 1321 k) Wall A = (1321) 1000 / 32940 Wall B = (1321) 1000 (0.11) / 15372 Wall C = (1321) 1000 (0.89) / 17568
40 psi < 85 10 psi < 85 67 psi < 85
Level 2 (V2 = 796 k) Wall A = (796) 1000 / 32940 Wall B = (796) 1000 (0.11) / 15372
24 psi < 85 6 psi < 85
My projects at Google earth
Senior Housing San Francisco - concrete shear walls
Stanford University Escondido Village Student Housing Concrete shear walls
Roxbury Condos, Beverley Hills
wood shear walls
Terrace Homes Hermosa Beach - wood shear walls
Terrace Homes Hermosa Beach - wood shear walls
Park City Village 1981 (Olympic Village 2002) wood shear walls
Park City Village 1981 (Olympic Village 2002) wood shear walls
2 0 0 2 e g a l l i V c i p m y l O a k a e g a l l i V y t i C k r
Level ski access
Park City Village Olympic Village 2002