AISC LRFD 1.pdf

250 FLANGES AND WEBS WITH CONCENTRATED FORCES [Comm. K1.such a distinction. For beams, a 2:1 stress gradient through the flange was used,whereas the gradient through column flanges was 2 1 2:1. In Section K1.3, the 2 1 2 :1gradient is used for both cases.This criterion applies to both bearing and moment connections.4. Web CripplingThe expression for resistance to web crippling at a concentrated force is a departurefrom earlier specifications (IABSE, 1968; Bergfelt, 1971; Hoglund, 1971; andElgaaly, 1983). Equations K1-4 and K1-5 are based on research by Roberts (1981).The increase in Equation K1-5b for N/d> 0.2 was developed after additional testing(Elgaaly and Salkar, 1991) to better represent the effect of longer bearinglengths at ends of members. All tests were conducted on bare steel beams withoutthe expected beneficial contributions of any connection or floor attachments. Thus,the resulting criteria are considered conservative for such applications.These equations were developed for bearing connections, but are also generallyapplicable to moment connections. However, for the rolled shapes listed in Part 1 ofthe LRFD Manual with F y not greater than 50 ksi (345 MPa), the web crippling criterionwill never control the design in a moment connection except for a W1250(W31074) or W1033 (W25049.1) column.The web crippling phenomenon has been observed to occur in the web adjacent tothe loaded flange. For this reason, a half-depth stiffener (or stiffeners) or ahalf-depth doubler plate is expected to eliminate this limit state.5. Web Sidesway BucklingThe web sidesway buckling criterion was developed after observing several unexpectedfailures in tested beams (Summers and Yura, 1982). In those tests the compressionflanges were braced at the concentrated load, the web was squeezed intocompression, and the tension flange buckled (see Figure C-K1.1).Web sidesway buckling will not occur in the following cases. For flanges restrainedagainst rotation:h/tl/bwf> 23 .(C-K1-1)BraceTension flangeWeb sideswaybuckleFig. C-K1.1. Web sidesway buckling.LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION