Experimental investigation of the damage characteristics and seismic response of moment-resisting bolted column base joints for precast concrete frames

Although several studies have been carried out on the development of bolted dry joints for precast concrete structures, damage assessment and seismic performance of bolted dry joints for column base joints under the different axial compression ratios have been rarely studied. In this study, six half-scale reinforced concrete columns, half of them were bolted connected and others were monotonically connected to the foundation, are subjected to combined cyclic lateral load and static axial compression load. The tests were carried out under three axial compression ratios: 0.10, 0.20, and 0.30. The seismic performances, including failure modes, lateral load-displacement responses, displacement ductilities, energy dissipation capacities, stiffness degradation behaviors, and moment-curvature responses, were evaluated and compared. The influence of axial compression ratio and reinforcement details on the seismic performance, plastic hinge characteristics, and damage assessment of specimens was also investigated in detail. The experiment results show that the increase of axial compression ratio from 0.1 to 0.3 increased the lateral load capacity, secant stiffness, and plastic hinge length while reducing the ductility. The efficiency of current formulations to predict plastic hinge length for the determination of plastic hinge length of specimens was also compared. Proposed damage descriptions for different performance levels (or damage states) were summarized and observed damage states correlated with drift ratio demands. Some modifications to the Park and Ang damage index for each damage state were proposed and stiffness reduction factors for the damage states were comparatively investigated. In addition, the displacement-based seismic capacities of this novel RC column base connection are presented in detail.