A simplified approach for evaluating second-order effects in low-rise steel-framed buildings

Abstract

Consideration of second-order effects is one of the most involved tasks in the analysis and design of steel-framed buildings. More specifically, the evaluation of amplified moments due to frame-level second-order effects is a very time consuming task because, depending on the method used, it may require an additional first-order analysis or the introduction of additional notional loads for each considered load case. Although the use of such methods may not present a problem when the design process is fully automated, hand calculations can be quite complicated for checking the results of a computer-generated design or for designing a small structure in which second-order effects may not even be significant enough to affect the selection of member sizes. This paper presents a simplified approach for the incorporation of second-order effects in the design of low-rise steel-framed structures. The development of this approach involved the design and analysis of a number of systems with various numbers of bays, floors and beam-span to floor-height ratios and included a thorough investigation of the effect of moment amplification on final member sizes. To facilitate this task, a spreadsheet application was developed to automate the design of a typical low-rise steel frame under given loading conditions. A parametric study was then performed to understand the effect of the various design parameters on member-level and frame-level second-order forces and moments. This led to the development of the simplified design approach proposed in this paper.