Experimental stiffness and seismic response of pallet-type steel storage rack connectors

The down-aisle lateral load-resisting systems of pallet-type steel storage racks are typically moment frames utilizing special beam-to-column moment-resisting connections. Both the stability and seismic response of racks are strongly influenced by the rotational stiffness developed by the beam-to-column connectors. The behavior of these connectors is poorly known, and consequently there is significant uncertainty as to proper values of connector stiffness and strength to use in design. This paper presents the results of down-aisle shake table tests performed on steel pallet-type storage racks fabricated from hot-rolled sections and incorporating four different bolted beam-to-column connectors. The main objectives of the tests were to determine appropriate static load connector rotational stiffness values from measured dynamic characteristics of storage racks under low amplitude vibrations, and to evaluate their response under quasi-static conditions as well as under strong earthquake ground motions. The experimental results suggest an initial static stiffness which degrades and recovers with small motions typical of in service conditions. This result may explain the poor repeatability of some testing protocols. For seismic motions, all rack specimens were able to undergo large inelastic deformations without compromising their load carrying capacity.