Hysteretic behavior of steel tubular web-concrete filled chord T-joints with spherical-cap gap under cyclic bending

Concrete filled steel tubes (CFST) can fully utilize the advantages of both steel and concrete to achieve superior ductility and strength. Therefore, an increasing number of CFST members are used as truss chords in bridge construction in earthquake zones. However, due to concrete settlement, concrete shrinkage, and temperature shift during service life, spherical-cap gaps may exist inside CFST chords, which will have an unfavorable influence on the seismic behavior of the web-chord connections. In this study, the hysteretic behavior of steel tubular T-joint with concrete-filled bottom chord with spherical-cap gap is experimentally investigated. A total of 24 T-joint specimens were tested with the CFST chord under the constant tensile load and the steel tubular web subjected to cyclic bending. The main testing parameters included spherical-cap gap ratios, chord to web diameter ratios, and chord diameter to thickness ratios. Based on the test results, the failure modes, hysteretic response, load-carrying capacity, stiffness degradation, ductility and energy dissipation characteristics were investigated and analyzed. The effect of spherical-cap gap on the hysteretic behavior of CFST T-joints was compared and discussed. The outcome of this research is expected to provide reference to the evaluation of seismic safety of CFST truss structures.