Exposed Column Base Connections for Minimizing Earthquake-induced Residual Deformations in Steel Moment-Resisting Framess

This paper proposes a new exposed column base (XCB) design concept for steel moment-resisting frames (MRFs) that promotes anchor rod yielding rather than plastic hinging at the bottom of the first story columns. A mechanics-based numerical model is first developed for simulating the complex XCB seismic behavior to further explore the design concept through simulations. Model validations with experimental data suggest that the proposed model is able to capture the hysteretic behavior of XCBs including yielding of each XCB component, contact and slip behavior, axial load – bending interaction, as well as their synergistic interaction. The new design concept is evaluated at the system-level by means of nonlinear response history analyses. The emphasis is placed on the earthquake-induced residual deformations of conventionally fixed base MRFs and those designed to promote anchor rod yielding. While global response quantities (e.g., peak story drift and residual lateral deformations) are nearly the same in both designs, local column base demands (e.g., residual column axial shortening) are considerably reduced when anchor rod yielding is promoted. From a repairability standpoint, the proposed concept shows promise and should be further explored in the future.