AISC LRFD 1.pdf

204 DESIGN COMPRESSIVE STRENGTHbehavior of columns designed using the ASD procedure. This includes cases withL / D ratios greater than 1.1.Equations E2-2 and E2-3 can be restated in terms of the more familiar slendernessratio Kl / r. First, Equation E2-2 is expressed in exponential form,F( 2) ù= éëexp -0.419lcr c y(C-E2-1)Note that exp(x) is identical to e x . Substitution of c according to definition of c inSection E2 gives,ûFForKl£ 4.71rEFyFcrìïé FyæKlö= íexp ê-0.0424Eçè r÷ï êëøî2ùüïúýFyúûïþ(C-E2-2)ForKl> 4.71rEFyFcr20.877p E=2æKlöçè r÷ø(C-E2-3)E3. DESIGN COMPRESSIVE STRENGTH FORFLEXURAL-TORSIONAL BUCKLINGTorsional buckling of symmetric shapes and flexural-torsional buckling ofunsymmetric shapes are failure modes usually not considered in the design ofhot-rolled columns. They generally do not govern, or the critical load differs verylittle from the weak axis planar buckling load. Such buckling loads may, however,control the capacity of symmetric columns made from relatively thin plate elementsand unsymmetric columns. Design equations for determining the strength of suchcolumns are given in Appendix E3. The AISC Design Guide, Torsional Analysis ofStructural Steel Members (Seaburg and Carter, 1997) provides an overview of thefundamentals and basic theory of torsional loading for structural steel members.Design examples are also included.Tees that conform to the limits in Table C-E3.1 need not be checked for flexural-torsionalbuckling.A simpler and more accurate design strength for the special case of tees and doubleanglesis based on Galambos (1991) wherein the y-axis of symmetry flexuralbucklingstrength component is determined directly from the column formulas.The separate AISC Specification for Load and Resistance Factor Design of Single-Angle Members contains detailed provisions not only for the limit state of compression,but also for tension, shear, flexure, and combined forces.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION