Inelastic Behavior of Direct RC Column to CFST Pile Connections

Abstract

Concrete filled steel tubes (CFSTs) are a composite structural component consisting of a steel tubewith concrete infill. Prior research has shown that CFST structural elements have greater strength and stiffness than typical reinforced concrete structural elements of similar size, result in economical structures, and also provide accelerated bridge construction. CFST members are quite suitable for piles and drilled shafts for deep foundations in bridge construction. While there has been both analytical and experimental research into CFST member behavior, there has been little research on connections of RC columns to CFST piles and drilled shafts. This research is an experimental study of a new connection between RC columns and CFST piles. In this research, half-scale column-to-pile connections were tested to evaluate their inelastic behavior under seismic loading. Four specimens were tested with the primary focus on the effects of (i) column reinforcement embedment depth, (ii) pile size, and (iii) the addition of a supplemental rib inside the pile. The nonlinear behavior was evaluated and the effects of these key parameters on the resistance, ductility, and deformation capacity were determined. The transfer of the force and moment from the RC column to the CFST pile were closely monitored. The experimental results were compared to nonlinear analyses performed with LS-Dyna computer program to calibrate models for future study and establish the accuracy of the models. The experiments found showed that the connections have excellent strength, ductility, and inelastic deformation capacity. The moment and force of the RC column were effectively transferred to the CFST pile with a nominal development length of the reinforcing bar. The test suggests that connections with a larger pile or a supplemental rib inside the pile, showed improved seismic performance, compared to connections with a smaller pile and no supplemental rib.