A Simplified Approach for Evaluating Second-Order Effects in Low-Rise Steel Framed Buildings

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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.