Cyclic performance of steel storage rack beam-to-upright bolted connections

Steel storage pallet racks are slender structures sensitive to the second-order effects. Therefore, the stability and seismic response of unbraced pallet racks are greatly influenced by the behaviour of the connections between pallet beams and uprights. In recent applications, a bolt has been installed in the otherwise boltless connections broadly used in pallet racks, in order to improve the behaviour of the connections and the stability of the overall structure. In this paper, an experimental study is presented to evaluate the cyclic performance of bolted connections in cold-formed steel storage pallet racks. Seven groups of bolted connections were tested under cyclic loads in a single pallet beam cantilever test setup. Upright thickness and beam height, the number of tabs and the number of bolts in the beam-end-connector were varied to assess their impact on the performance of a bolted pallet beam-to-upright connection. The moment-rotation hysteretic and backbone curves of all tested connections were obtained, as were the behavioural factors corresponding to their stiffness degradation, ductility and energy dissipation capacity. The focus of the paper is to investigate the cyclic behaviour of steel storage rack beam-to-upright bolted connections, and to identify the most significant influencing geometric parameters. Comparisons of the cyclic response and failure modes between connections with and without bolts are also provided. Finally, based on the experimental results, the so-called Pinching4 model is used to characterise the hysteretic performance of bolted pallet beam-to-upright connections for further use in the design by advanced analysis of rack structures under seismic loads.