BEHAVIOR OF WEB-TAPERED BUILT-UP I-SHAPED BEAMS

Appendix F of the AISC-LRFD Specification governs the design of web-tapered I-shaped beams. These design provisions are restricted to beams with equal flange areas and non-slender webs. However, the current practice in the low-rise metal building industry is to employ flanges of unequal area and slender webs; a time honored practice that has resulted in safe and economical structures. The current study utilizes validated nonlinear finite element analysis techniques to predict the flexural response and corresponding limit states associated with mild-carbon steel doubly-symmetric web-tapered I-shaped beams. A parametric study is performed to study the moment capacity and flexural ductility in the inelastic range of various beam geometries with length-to-depth ratios between two and three (i.e. what one normally encounters in the rafter sections of a low-rise metal building gable frame). Compactness criteria that ensure attainment of a rotation capacity equal to three are examined and results tabulated. A comparison is made between the Specification design provisions and the ultimate moment capacity and structural ductility predicted by the finite element method. Conclusions are made regarding the effects of plate slenderness on the behavior of the nonprismatic beam models. Recommendations are made for further research of singly-symmetric web-tapered beams