Experimental stiffness of pallet-type steel storage rack tier drop connectors

The down-aisle lateral load-resisting systems of pallet-type steel storage racks are, typically, frames utilizing special beam-to-column moment-resisting connections. The behavior of these connectors is poorly understood, and consequently, there is significant uncertainty as to proper values of connector stiffness and strength to use in design. This technical note presents the results of down-aisle shake table tests performed on steel pallet-type storage racks fabricated from cold-formed sections and incorporating two different teardrop beam-to-column connector systems. This study is a follow up on a previous experimental investigation on bolted beam-to-column connectors by the same authors. 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. The experimental results indicated that the beam-to-upright-connector stiffness values reduce with excitation amplitude. While the connector stiffness decreased significantly during the most intense shaking, it recovered almost all of its initial values at the completion of each test. Unlike the bolted connections, the stiffness recovered immediately without the need for low-level white-noise excitation to "settle in" the connector prior to full recovery of the initial stiffness.