Experimental and Theoretical Study on High Strength Steel Extended Endplate Connections After Fire

In order to reveal more information and better understanding on the behavior and failure mechanisms of high strength steel (HSS) extended endplate connections at ambient temperature and after fire, an experimental and theoretical study has been conducted and presented in this paper. The provisions of Eurocode 3 are verified with the test results. Because strength of bolts decreases more rapidly than that of structural steels, failure modes of endplate connections may change after fire. Hence, a series of equations are proposed to predict failure modes of endplate connections after fire. Furthermore, FE simulations which can predicate the performance of HSS extended endplate connections with reasonable accuracy are adopted to study the behaviors of the connections after cooling down from various fire temperatures and to validate the accuracy of the proposed equations. Moreover, a parametric study is carried out to explore an optimization design method. It is found that the current provisions of EC3 can justifiably predict failure modes and plastic flexural resistances of HSS extended endplate connections both at ambient temperature and cooling down from 550 °C, but it is not the case for their initial rotational stiffness and rotation capacity. In order to avoid brittle failure mode of endplate connections after fire, appropriately increasing the diameter or grade of bolts in the design is suggested. What is more, the match of steel grade and thickness of column flange and endplate as well as beam should be considered in the optimization design of beam-column endplate connections.