Design and behavior of recentering beam-to-CFT column connections with super-elastic shape memory alloy fasteners

Abstract

This study investigates the performance of new composite (steel-concrete) moment connections through numerical simulations. The innovative aspects of this research lay in the use of end-plate connections between steel beams and concrete-filled tube (CFT) columns that utilize a combination of low-carbon steel and shape memory alloy (SMA) components. In these new connections, the intent is to use the recentering effect provided by super-elastic SMA tension bars to reduce the level of building damage and residual drift after a major earthquake. The low-carbon steel components provide excellent energy dissipation. The analysis and design of these structures is complicated because the connections cannot be modeled as being simply pins or full fixity ones; they are partial restraint (PR). A refined finite element (FE) model with sophisticated three dimensional (3D) solid elements was developed to perform numerical experiments on the PR-CFT joints with a view to obtaining the global behavior of the connection. Based on the behavioral information obtained from these FE tests, simplified connection models were formulated using 2D joint elements with nonlinear spring components. The behavior of entire connections under cyclic loads was examined. The results were compared with the connection behavior obtained from the 3D FE simulations and corresponding connection tests. Good agreement was found between the simple and sophisticated models, confirming the robustness of the approach.