An experimental program was undertaken to investigate the inelastic seismic response of metal deck roof diaphragm systems. The load carrying capacity of roof diaphragms subjected to lateral loads is directly dependent on the shear strength of the connections. Hence, as part of this larger research program, a study on the inelastic performance of arc-spot welded deck-to-frame connections was completed. The connection project involved the monotonic, cyclic and seismic testing of 235 specimens, with and without weld washers, with different electrode types, and with various steel deck and frame thicknesses. Currently, welded washer connections are recommended for the improvement of weld quality and connectivity when thin deck material (t ≤ 0.71 mm) is to be connected to the frame of the structure, not for the improvement of seismic performance. In general, the test results indicate that welded connections with washers exhibit higher ultimate capacities, as well as increased ductility and energy absorption ability in comparison with washerless connections. To achieve this performance, it is important to ensure that proper welding protocol is followed so that sufficient penetration into the frame material is obtained, especially for the thicker 1.21 and 1.52 mm sheet steels.
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