Optimal Design of W-Shape Members Subjected to Combined Forces

Abstract

Design of members subjected to combined forces is an iterative process in which the designer selects a trial section and checks the selection for compliance with the appropriate provisions of AISC Specification for Structural Steel Buildings Chapter H. This process is repeated until a desired section is identified. The introduction of AISC Steel Construction Manual Table 6-1 has made the calculations involved in checking different trial sections considerably easier and faster. However, there is still no comprehensive resource for the designer to select an initial trial section for various scenarios of members subjected to combined forces which leads to an optimal final selection quickly. This paper presents a method and aids for more rational and efficient selection of trial sections for W-shapes subject to combined compression and bending about one or two principal axes, tension and bending about one or two principal axes, or biaxial bending. Unlike some previous methods, there are no limitations on the values of unbraced and effective lengths (e.g., requiring that L_b = L_cy). The design aids are developed for all W-shapes in Grade 50 steel using both LRFD and ASD methods. The method presented converges quickly, reducing the need for multiple repeated calculations before a final W-shape is selected. Example problems are also included.