AISC LRFD 1.pdf

Sect. B10.] PROPORTIONS OF BEAMS AND GIRDERS 15Stiffened ElementsTABLE B5.1 (cont.)Limiting Width-Thickness Ratios forCompression ElementsDescription of ElementFlanges of rectangular boxand hollow structural sectionsof uniform thickness subjectto bending or compression;flange cover plates and diaphragmplates between linesof fasteners or weldsfor uniform compressionfor plastic analysisUnsupported width of coverplates perforated with a successionof access holes [b]Webs in flexuralcompression [a]Webs in combined flexuraland axial compressionAll other uniformly compressedstiffened elements, i.e.,supported along two edgesCircular hollow sectionsIn axial compressionIn flexure[a] For hybrid beams, use the yieldstrength of the flange F yf insteadof F y .[b] Assumes net area of plate atwidest hole.[c] Assumes an inelastic rotationcapacity of 3 radians. For structuresin zones of high seismicity, a greaterrotation capacity may be required.[d] For plastic design use 0.045E/F y .WidthThicknessRatiob / tb / th / t w p(compact)Limiting Width-Thickness RatiosLRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTIONNA r(noncompact)h / t w for P u / b P y 0.125 [c],[g] [h]E ⎛ 2.75P⎞u3.76 1−F ⎜ ⎟y ⎝ φbPy⎠ E ⎛ P ⎞u5.70 −for P u / b P y > 0.125 [c][g]1 0.74⎜F⎟y ⎝ fbPy⎠E ⎛ P ⎞u112 . 233 . −⎜F φ ⎟y bPyb / th / t wD / t3.76 E / F y[c], [g]≥ 149 .1.12 E / F y⎝FyNA1.40 E / F y0.939 E / F y-E1.86 E / F y5.70 E / F y[h][d]NA0.11E / F y0.07E / F y 0.31E / F y[e] F L = smaller of (F yf –F r )orF yw , ksi (MPa)[e] F r = compressive residual stress in flange[e] F L = 10 ksi (69 MPa) for rolled shapes[e] F L = 16.5 ksi (114 MPa) for welded shapes4[f] k c = and 0.35 k c 0.763h / t w[g] For members with unequal flanges, use h p insteadof h when comparing to p .[h] For members with unequal flanges, see Appendix B5.1.⎠149 . E/FyAssumes an inelastic ductility ratio (ratio of strain at fracture to strain at yield) of 3. When the seismic response modificationfactor R is taken greater than 3, a greater rotation capacity may be required.Errata9/4/01Errata9/4/01