Carbon steel and stainless steel bolted connections undergoing unloading and re-loading processes

A total of 50 bolted connections of carbon steel and stainless steel subjected to monotonic loading and cyclic loading conditions were investigated. The connection specimens were fabricated from carbon steel grades 1.20 mm G500 and 1.90 mm G450, as well as cold-formed stainless steel types EN 1.4301 and EN 1.4162 with nominal thickness 1.50 mm. In the monotonic tests, the specimens were tested under a constant loading rate by the displacement control test method, while in the cyclic tests, the specimens having the same dimensions as those in the monotonic tests were subjected to loading, unloading and re-loading processes, where displacement control and load control test methods were used. The results obtained from the cyclic tests were compared with those obtained from the monotonic tests. It was found that the ultimate loads obtained from the cyclic tests were, on average, larger than those obtained from the monotonic tests for carbon steel bolted connections; this was in contrast with the compared results for stainless steel bolted connections. The elongations corresponding to the ultimate loads obtained from the cyclic tests were, on average, larger than those obtained from the monotonic tests for both carbon steel and stainless steel, which may indicate that the loading processes in the cyclic tests generally delayed the bolted connection specimens from reaching the ultimate loads. Generally, the failure modes in the cyclic tests were consistent with those in the monotonic tests for the same specimen series, where the specimens mainly failed in the connection plate bearing.