Transcript
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Braced frame Copyright Prof Schierle 2011 1
Brac ed f ram eA ColumnB Beam
D Brace
E Gusset plate
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Eight-story steel braced frame
Assume
High strength steel (yield strength Fy = 50 ksi ) Fy = 50 ksi
Average wind pressure P = 30 psfGravity load = 50 psf Column (psf) Beam (psf) Brace (psf)
DL 70 70 70
Column load (per foot on beam)
w = 90 psf x 30/1000 w = 2.7 klf
Beam load
w = 95 psf x 30/1000 w = 2.85 klf
Base shearV = 30 psf x 45 x 90/1000 V = 122 k
Overturn moment M
M = 122 k x 51 M = 6222 k
Column Plateral = M/30 Pgravity = n w Atributary Pa + d P = 0 P = 8x2.7x15 = 324 k 324 k
h=96-6=
90
51
Brace force (see vectors) P = 78 k
Note: brace alters from tension to compressiondesign for compression, due to buckling
3045
V=122 k
LL 50x0.4 = 20 50x0.5 = 25 50
Total 90 95 120
b + c P=6222 k/30= 207 k P = 8x2.7x30 = 648 k 855 k
V=122 k
P=78 kP=78 k
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Column P KL length Use Pall vs. P
a + d 324 k 12 W14x61 410 > 324
Brace 78 k 20 W14x43 117 > 78b + c 855 k 12 W14x120 919 > 855
Column and brace design (use AISC column table)
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Bending moment
M = wL2/8 = 2.85 klf x 302/8 M = 321 k
Section Modulus
S = M/Fb = 321 kx12/ 30 ksi S = 128 in3
Use W18x76 146 > 128Deflection = (5/384) W L3/ (E I)
= (5/384) (2.85x30) (30x12)3/ (30,000x1330) = 1.3
allowable = L/240 = (30x12)/240 = 1.5 1.5 > 1.3, ok
Note: while the center bay beams are supported by braces,
UBC requires such beams to be designed without brace supportB
m
d
g
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Design 4th story columnsAssume
High strength steel (yield strength Fy = 50 ksi ) Fy = 50 ksi
Average wind pressure P = 30 psfGravity load = 50 psf Column (psf) Beam (psf) Brace (psf)
DL 70 70 70
Column load (per foot on beam)
w = 90 psf x 30/1000 w = 2.7 klf
Beam load
w = 95 psf x 30/1000 w = 2.85 klf
4th floor shear VV = 30 psf x 45 x 3.5 x 12/1000 V = 56.7 k
Overturn moment M
Lever arm = 3.5x12/2+6 = 27
M = 56.7 k x 27 M = 1531 kColumn Plateral = M/30 Pgravity = n w Atributary P
27
Brace force (use vectors) P = 36 k
LL 50x0.4 = 20 50x0.5 = 25 50
Total 90 95 120
b + c P=1531 k/30= 51 k P = 4x2.7x30 = 324 k 375 kV=56.7 k
P=36 kP=36 k
a + d P = 0 P = 4x2.7x15 = 162 k 162 k
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Column P KL length Use Pall vs. P
b + c 375 k 12 W14x61 410 > 375
Column and brace design (use AISC column table)
Brace 36 k 20 W8x31 97 > 36
a + d 162 k 12 W8x31 189 > 162
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First interstate Bank Los Angeles
Architect: I M Pei
Engineer: CBM
Combines framed tube exteriorwith braced core
Moment frame Braced frame Combined
drift drift drift
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1 IBM bui lding PittsburghArchitect: Curtis and Davis
Engineer: Worthington & Skilling
2 Alcoa bui ld ing San Francisco
Architect/Engineer: SOM
3 Federal Reserve Banc Boston
Architect: Hugh StubbinsEngineer: Le Messurier
1 Onterie Center Chicago
Architect/Engineer: SOM
2 Proposed 142 story tower ChicagoArchitect: Kay Vierk Janis
Ex
pres
sed
brac
ing
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John Hancock tower Chicago
Architect/Engineer: SOM
Braced tube
AT&T tower, Seattle
Architect: Basetti et all
Engineer: Skilling et all
Braced superstructure with4 columns of 12 ksi high strength
concrete in 10 steel tubes
Bank of China Hong Kong
Architect: I M Pei
Engineer: Ove Arup
Braced superstructure definesarchitectural form
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b
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Alcoa Building San Francisco
Architect/Engineer: SOM
John Hancock Tower Chicago
Architect/Engineer: SOM
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joinsexteriorcolumnstotransfersheartoreducedrift
1 Georgia-Pacific tower, Atlanta
Architect: SOM
Engineer: Weidlinger Associates
2 Barcelona hotel
Architect: SOM
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Large drift
(unglued boards resist independently)
Small drift
(glued boards resist in synergy
shear joins tension & compression)
Gue-lam beam anlogy
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Barcelona Hotel Hong Kong-Shanghai Bank
Bel t t russ / Out r igger
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Visc o elas t i c b rac inghttp://ascelibrary.org/emo/resource/1/jenmdt/v129/i6/p597_s1?isAuthorized=no
www.dist.unina.it/proc/1998/ECEE11/ECEE11/T5/PAOODO.PDF
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Ch M h tt B N Y k C t T T k
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Chase Manhattan Banc New YorkArchitect / Engineer: SOM
Century Tower TokyoArchitect: Norman Foster
Engineer: Ove Arup
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cc en t r i c b raced f r am e
LA courthouse @ 105 / 405features twin link-beams
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LA courthouse @ 105 / 405
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LA courthouse @ 105 / 405
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