Performance of Unstiffened welded steel I-beam to hollow tubular column connections under seismic loading

Earthquake causes wide and severe damage to building structures, due to not just the great ground motion but also secondary actions, such as impact, blast or fire, occurring after earthquake. The extreme combined loading scenario should be considered for safety of buildings and lives. Taking fire for example, the combined load can be considered as an event in which the structures are first partially damaged under an earthquake and then attacked by fire. In order to investigate the post-earthquake loading scenario, it is important to assess the partial damage caused by earthquake on different components of structures. The behavior of welded steel I-beam to hollow square tubular columns is investigated herein. A detailed experimental study is presented in which two groups of unstiffened welded steel connections, with the same configurations, subjected to static and cyclic loading are considered. The flexibility and strength of the connections are measured, while the damage phenomena and failure modes are explored during the tests. The connection damage is found to be a cumulative fracture developing process which leads to significant gradual degradation of the mechanical properties of the connection. The quantificational evaluations of the cyclic loading induced damage are also carried out to investigate the connection damage level according to different loading intensities. A finite element modeling numerical study is also carried out to validate the experimental results and a good agreement is achieved. The test results and FE modeling provide a benchmark data for the unstiffened welded connections and can be used for further investigations of the connections subjected to combined actions such as post-earthquake fire.