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Braced frame Prof Schierle 1Braced frameA ColumnB BeamD BraceE Gusset plateBraced frame Prof Schierle 2Eight-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 70Column load (per foot on beam)w = 90 psf x 30’/1000 w = 2.7 klfBeam loadw = 95 psf x 30’/1000 w = 2.85 klfBase shearV = 30 psf x 45 x 90’/1000 V = 122 kOverturn moment MM = 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 kh = 96-6 = 90’51’Brace force (see vectors) P = 78 kNote: brace alters from tension to compression design for compression, due to bucklingV=122 kLL 50x0.4 = 20 50x0.5 = 25 50Total 90 95 120b + c P=6222 k’/30’= 207 k P = 8x2.7x30 = 648 k 855 kV=122 kP=78 kP=78 kBraced frame Prof Schierle 3Column P KL length Use Pall vs. Pa + d 324 k 12’ W14x61 410 > 324Brace 78 k 20’ W14x43 117 > 78b + c 855 k 12’ W14x120 919 > 855Column and brace design (use AISC column table)Braced frame Prof Schierle 4Bending momentM = wL2/8 = 2.85 klf x 302/8 M = 321 k’Section Modulus S = M/Fb = 321 k’x12”/ 30 ksi S = 128 in3Use 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, okNote: while the center bay beams are supported by braces, IBC requires such beams to be designed without brace supportBeam designBraced frame Prof Schierle 5Design 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 70Column load (per foot on beam)w = 90 psf x 30’/1000 w = 2.7 klfBeam loadw = 95 psf x 30’/1000 w = 2.85 klf4thfloor 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 Plateral = M/30’ Pgravity = n w Atributary  P27’Brace force (use vectors) P = 36 kLL 50x0.4 = 20 50x0.5 = 25 50Total 90 95 120b + c P=1531 k’/30’= 51 k P = 4x2.7x30 = 324 k 375 kV=56.7 kP=36 kP=36 ka + d P = 0 P = 4x2.7x15 = 162 k 162 kBraced frame Prof Schierle 6Column P KL length Use Pall vs. Pb + c 375 k 12’ W14x61 410 > 375Column and brace design (use AISC column table)Brace 36 k 20’ W8x31 97 > 36a + d 162 k 12’ W8x31 189 > 162Braced frame Prof Schierle 7Structural bracing optionsregarding number of joints and brace lengthArchitectural bracing optionsregarding locations of openingsBraced frame Prof Schierle 8Bracing configurationsFirst interstate Bank Los AngelesArchitect: I M PeiEngineer: CBMCombines framed tube exteriorwith braced coreMoment frame Braced frame Combineddrift drift driftBraced frame Prof Schierle 91 IBM building PittsburghArchitect: Curtis and DavisEngineer: Worthington & Skilling2 Alcoa building San FranciscoArchitect/Engineer: SOM3 Federal Reserve Banc BostonArchitect: Hugh StubbinsEngineer: Le Messurier 1 Onterie Center ChicagoArchitect/Engineer: SOM2 Proposed 142 story tower ChicagoArchitect: Kay Vierk JanisExpressed bracingBraced frame Prof Schierle 10John Hancock tower ChicagoArchitect/Engineer: SOMBraced tubeAT&T tower, SeattleArchitect: Basetti et allEngineer: Skilling et allBraced superstructure with4 columns of 12 ksi high strength concrete in 10’  steel tubes Bank of China Hong KongArchitect: I M PeiEngineer: Ove ArupBraced superstructure defines architectural formBraced frame Prof Schierle 11Expressed bracingAlcoa Building San FranciscoArchitect/Engineer: SOMJohn Hancock Tower ChicagoArchitect/Engineer: SOMBraced frame Prof Schierle 12Belt truss/outriggerjoins exterior columns to transfer shear to reduce drift1 Georgia-Pacific tower, AtlantaArchitect: SOMEngineer: Weidlinger Associates2 Barcelona hotelArchitect: SOMBraced frame Prof Schierle 13Large drift(unglued boards resist independently)Small drift (glued boards resist in synergyshear joins tension & compression)Gue-lam beam anlogyBraced frame Prof Schierle 14Barcelona HotelHong Kong-Shanghai BankBelt truss / OutriggerBraced frame Prof Schierle 15Visco elastic bracinghttp://ascelibrary.org/emo/resource/1/jenmdt/v129/i6/p597_s1?isAuthorized=nowww.dist.unina.it/proc/1998/ECEE11/ECEE11/T5/PAOODO.PDFBraced frame Prof Schierle 16Eccentric braced frame(Adjusts stiffness between flexible moment frame and stiff braced framee = link beam (short link beam  stiff; long link beam  flexible frame Eccentric braced detailsA Column; B beam; C brace; D gusset plate; E stiffener platesBraced frame Prof Schierle 17Chase Manhattan Banc New YorkArchitect / Engineer: SOM Century Tower TokyoArchitect: Norman FosterEngineer: Ove ArupBraced frame Prof Schierle 18Eccentric braced frame LA courthouse @ 105 / 405features twin link-beamsBraced frame Prof Schierle 19LA courthouse @ 105 / 405Braced frame Prof Schierle 20LA courthouse @ 105 / 405Braced frame Prof Schierle


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USC ARCH 613L - 09-braced-frame

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