Influence of mechanical and geometric uncertainty on the seismic performance of cold-formed steel braces with additional holes

Abstract

Steel storage pallet racks are used worldwide for the storage of palletized goods. They are typically braced to improve their structural stability and seismic performance. Braces may be fabricated with additional holes (perforations) at the brace ends to satisfy design and detailing requirements for capacity protection of frames with concentric X bracings. The ratio of overstrength to slenderness is particularly critical. This paper aims to evaluate the influence of specific perforated brace detailing and randomness in the geometrical features and mechanical properties on the overall structural response of the system. Variability in member geometric features was determined from current design specifications, while variability in steel mechanical properties was determined via experimental testing. Via a sensitivity analysis uncertainty in cross-section thickness and flange width are identified as the most critical features, motivating greater accuracy in the manufacturing process. The impact of statistical variation in design parameters on the yield load, ultimate load and ductility is further elucidated through a Monte Carlo simulation, which enables quantification of the influence of the size and number of holes on the member structural response. The effect on ductility of the member cross-section class and slenderness is also explored. To promote utilization of perforated braces in seismically-active areas, the work concludes with recommendations for design and determination of the ductility factor. Finally, a reliability analysis of non-dissipative connections is performed, providing the reliability index, β.