Cyclic behaviour of partially prefabricated concrete-encased-and-filled steel tubular columns with rebar-to-steel plate lap splices

This paper investigates the cyclic performance of concrete-encased-and-filled steel tubular (CFEST) columns using rebar-to-steel plate lap splice connections for foundation and beam-column joint applications. The proposed connection simplifies fabrication and on-site assembly by avoiding complex mechanical couplers and welding. Quasi-static cyclic tests were conducted on seven CFEST columns and one conventional reinforced concrete (RC) column. The main variables were lapped rebar diameter, lap splice length, tie bar diameter, shear stud configuration and the axial compression ratio. The CFEST columns showed superior damage tolerance compared with the RC column, with limited external damage in the high-ductility concrete shell at large drift demands. Because bond degradation caused slip of the lapped rebars during cyclic loading, the CFEST columns developed larger column-base rotation than the RC column. The tests confirm that bond performance in the lap region governs the cyclic behavior of CFEST columns. Insufficient lap splice length or lack of tie bars caused severe rebar slip at later loading stages, leading to accelerated strength degradation and reduced deformation and energy dissipation capacities. Based on the experimental and analytical results, design recommendations are proposed. A sectional capacity design method is developed using the plastic stress distribution method. Among the examined code provisions, ACI 318–25 provided the most suitable and conservative basis for lap splice length and tie bar design. To ensure reliable shear transfer at the steel tube-to-core concrete interface, the total shear resistance of tie bars and shear studs should be no less than 125% of the yield force of the lapped rebars.