Second-Order Analysis of Slender Steel Frames under Distributed Axial and Member Loads

In certain types of steel framed structures members can be subjected to significant distributed axial as well as lateral loads along their lengths. The behavior of the member is complicated by the nonlinear interaction between the member force and the member stiffness. The conventional assumption of lumping loads to the member ends can lead to inaccurate results. This paper addresses the second-order analysis of frames with members subjected to gravitational axial loads. The error associated with lumping of distributed loads at the members ends is shown to be nontrivial in certain cases. In most design codes axial loads are assumed to be nodal and do not vary along the member length. Also, the result of previous studies on second-order frame analysis ignores this influence and, therefore, their solutions are only approximate and may be incorrect. The derived element improves the accuracy and widens the scope of application for a computer program based on the concept of “second-order analysis,” the “advanced analysis,” and the proposed “integrated analysis and design approach,” which carries out an analysis simultaneously with design meeting the design code requirements. This proposed approach differs from other available methods for advanced analysis in its simplicity and capability of meeting the current and the widely used design code philosophy based on the first-plastic-hinge concept.