Hysteretic Model for Exposed Column-Base Connections

A hysteretic model formulation is presented for simulation of the cyclic moment-rotation response of exposed column-base (ECB) connections, which are typically used to connect a steel column to a concrete footing in steel moment-resisting frames. The research is motivated by the potential for using these connections as dissipative elements within seismic design. The physical processes responsible for various forms of hysteretic response are outlined; these include: (1) seating and gapping between the base plate and footing leading to pinched hysteresis, and (2) a recentering effect of axial compressive load resulting in flag-shaped hysteresis. The proposed ECB model utilizes: (1) a trilinear backbone curve; (2) hysteretic rules for pinching, unloading, recentering, and reloading; and (3) modes of deterioration for four quantities, including strength and stiffness. The model has 16 parameters, of which 4 are classified as core parameters (meaning they can be determined through physics-based models), whereas 12 are classified as ancillary, such that they require empirical calibration. The model is fit to a series of experiments, and it is determined that it is able to simulate the key aspects of hysteretic response. Recommendations for calibration of model parameters are presented, and limitations of the model are outlined.