No Slide Title Systems/28-braced...w = 90 psf x 30’/1000 w = 2.7 klf ... 3 Federal Reserve Banc Boston Architect: Hugh Stubbins ... ↑for previous slide 10 John Hancock tower Chicago

Braced frame Copyright © G G Schierle, 2001-04 press Esc to end, ↓ for next, ↑ for previous slide 1

Braced frameA Column

B Beam

D Brace

E Gusset plate


Eight-story steel braced frameAssumeHigh strength steel (yield strength Fy = 50 ksi ) Fy = 50 ksiAverage 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 klfBeam loadw = 100 psf x 30’/1000 w = 3 klfBase shearV = 30 psf x 45 x 90’/1000 V = 122 kOverturn moment MM = 122 k x51’ M = 6222 k’

Column P lateral = M/30’ P gravity = n w A tributary Σ Pa + d P = 0 P = 8x2.7x15 = 324 k 324 k

h =

96-

6 =

90’

51’

Brace force (see vectors) P = 78 kNote: brace alters from tension to compression

design for compression, due to buckling

30’45

’

V=122 k

LL 50x0.4 = 20 50x0.6 = 30 50Total 90 100 120

b + c P=6222 k’/30’= 207 k P = 8x2.7x30 = 648 k 855 k

V=122 k

P=78 kP=78 k


Column P KL length Use Pall vs. Pa + 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)


Bending momentM = wL2/8 = 2.7 klf x 302/8 M = 304 k’Section Modulus S = M/Fb = 304 k’x12”/ 30 ksi S = 122 in3

Use W18x71 127 > 122Deflection Δ = (5/384) W L3/ (E I)Δ = (5/384) (2.7x30) (30x12)3/ (30,000x1170) Δ = 1.4”Δallowable = L/240 = (30x12)/240 = 1.5 1.5 > 1.4, okNote: while the center bay beams are supported by braces, UBC requires such beams to be designed without brace supportB

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Design 4th story columnsAssumeHigh strength steel (yield strength Fy = 50 ksi ) Fy = 50 ksiAverage 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 klfBeam loadw = 100 psf x 30’/1000 w = 3 klf4th floor shear VV = 30 psf x 45 x 3.5 x 12’/1000 V = 56.7 kOverturn moment MLever arm = 3.5x12’/2+6’ = 27’M = 56.7 k x 27’ M = 1531 k’

Column P lateral = M/30’ P gravity = n w A tributary Σ P

27’

Brace force (use vectors) P = 36 k

LL 50x0.4 = 20 50x0.6 = 30 50Total 90 100 120

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


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 AngelesArchitect: I M PeiEngineer: CBM

Combines framed tube exterior with braced core

Moment frame Braced frame Combineddrift drift drift


1 IBM building PittsburghArchitect: Curtis and DavisEngineer: Worthington & Skilling

2 Alcoa building San FranciscoArchitect/Engineer: SOM

3 Federal Reserve Banc BostonArchitect: Hugh StubbinsEngineer: Le Messurier

1 Onterie Center ChicagoArchitect/Engineer: SOM

2 Proposed 142 story tower ChicagoArchitect: Kay Vierk JanisE

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John Hancock tower ChicagoArchitect/Engineer: SOM

Braced tube

AT&T tower, SeattleArchitect: Basetti et allEngineer: Skilling et all

Braced superstructure with4 columns of 12 ksi high strength concrete in 10’ φ steel tubes

Bank of China Hong KongArchitect: I M PeiEngineer: Ove Arup

Braced superstructure defines architectural form


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John Hancock Tower ChicagoArchitect/Engineer: SOM


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1 Georgia-Pacific tower, AtlantaArchitect: SOMEngineer: Weidlinger Associates

2 Barcelona hotelArchitect: SOM


Barcelona Hotel Hong Kong-Shanghai Bank

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Eccentric braced frame LA courthouse @ 105 / 405

features twin link-beams

No Slide Title Systems/28-braced...w = 90 psf x 30’/1000 w = 2.7 klf ... 3 Federal Reserve Banc Boston Architect: Hugh Stubbins ... ↑for previous slide 10 John Hancock tower Chicago

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