Cyclic Experiments on Sidelap and Structural Connectors in Steel Deck Diaphragms

Abstract

This work studied the cyclic shear performance of connectors used for sidelap and structural connectors in bare steel deck roof diaphragms. Typical bare steel deck roof diaphragms include thousands of such connections, and knowledge of the connection shear performance is important for understanding and predicting diaphragm performance under seismic loads. The experimental program included four types of sidelap connectors: screw nestable, top arc seam weld, button punch, and the proprietary PunchLok II crimp. The testing included three types of structural connectors: power-actuated fasteners, arc spot welds, and arc seam welds. A total of 64 sidelap and 60 structural connector tests were performed under a cyclic loading protocol, to evaluate behavior at small deformations as well as under large excursions, providing the shear response up to and through the peak response, including postpeak response until material separation and failure. The connection test results were used to establish experimental multilinear backbone curves. From these backbone curves, average connection shear stiffness, strength, and ductility can be estimated and compared for all studied configurations. The connection response for the mechanical connections and welded connections exhibited significantly different behavior, particularly in terms of postpeak ductility and residual force. The connector backbone response is appropriate for use as nonlinear shear springs to model the response of the connections in high-fidelity models of bare steel deck roof diaphragms.