Effects of pinching on seismic performances of unbraced steel storage pallet racks

Abstract

Cold-formed steel storage unbraced pallet racks are generally used to store goods in large warehouses, and the existing full-scale shaking table tests show that a typical unbraced pallet rack exhibits a global failure mechanism with damaged connections and undamaged structural members. Therefore, the significant pinching of beam-to-upright connections has a significant influence on the structural seismic performance. The paper presents a numerical investigation into the effects of pinching on seismic performances of unbraced steel storage pallet racks. A FE model of cold-formed steel storage pallet racks subjected to seismic loads is developed to perform non-linear time-history analyses via OpenSees. The full-scale shaking table test results are employed to validate the FE model. Various connection models, including the modified Pinching 4 connection model, the hysteretic model, and the elastic model, are implemented in the simulation. The structural seismic performances based on different connection models are then compared. In particular, the connection behaviours defined by the modified pinching and hysteretic models are presented and compared. Moreover, the corresponding damage index (DI) of a typical connection is also calculated based on two different damage models. The results show that the pinching of connections greatly increases the structural seismic response in respect to the global displacement and interstorey drift, and should be carefully considered in the seismic design of cold-formed steel storage unbraced pallet racks.