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AISC LRFD 1.pdf

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App. E3.] DESIGN COMPRESSIVE STRENGTH 95ép2wFe= ê + GJ Kl2 ú(z) Ix+ IyëECùû1(A-E3-5)(b) For singly symmetric shapes where y is the axis of symmetry:Fey + F æez4FeyFezHöFe= ç 1- 1-÷2 H è ( Fey+ F 2ez) ø(A-E3-6)(c) For unsymmetric shapes, the critical flexural-torsional elastic buckling stressF e is the lowest root of the cubic equation2 22æxöo 2æyöo( Fe -Fex)( Fe -Fey)( Fe -Fez)-Fe ( Fe -Fey) ç-Fe ( Fe - Fex) = 0è r ÷o øçè r ÷o ø (A-E3-7)whereK z = effective length factor for torsional bucklingG = shear modulus, ksi (MPa)C w = warping constant, in. 6 (mm 6 )J = torsional constant, in. 4 (mm 4 )I x , I y = moment of inertia about the principal axes, in. 4 (mm 4 )x o , y o = coordinates of shear center with respect to the centroid, in. (mm)Ix+ I2 2 2 yro = xo + yo+Ax yH = 1- æ + öçè ÷ø2 2o o2ro(A-E3-8)(A-E3-9)Fex2p E=( Kl/ r)xx2(A-E3-10)FezFey2p E=( Kl/ r)2æpEC ö= ç + GJ( Kl)÷èzyy21w2 2ø Aro(A-E3-11)(A-E3-12)A = cross-sectional area of member, in. 2 (mm 2 )l = unbraced length, in. (mm)K x , K y = effective length factors in x and y directionsr x , r y = radii of gyration about the principal axes, in. (mm)= polar radius of gyration about the shear center, in. (mm)r o<strong>LRFD</strong> Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION

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