STUDY ON BENDING BEHAVIOR OF CIRCULAR UHPC FILLED HIGH STRENGTH STEEL TUBE BEAMS

Taking the steel content and hoop coefficient as test parameters, the pure bending tests of 5 circular ultra-high performance concrete (UHPC) filled high strength steel tube (UFHST) beams and 2 circular UHPC filled normal strength steel tube (UFST) beams were carried out to investigate their bending behaviors. The experimental results show that UFHST beams failed in ductile. The composite section satisfied the assumption of plane cross-section. The hoop action of the high strength steel tube on UHPC should be considered in the compression zone. Compared with the normal strength steel tube, high strength steel tube can restrain the transverse expansion of UHPC more effectively. The finite element model verified by test results was used to conduct parameter analysis of the hoop coefficient. When the concrete-filled steel tube beam reaches its bending bearing capacity, the corresponding neutral axis and the stresses of steel and concrete are related to the hoop coefficient. With the increase of the hoop coefficient, the neutral axis keeps moving toward the section centerline; there is a decrease in the steel stress in the tensile zone, and an increase in the steel stress and concrete stress in the compressive zone. It was inaccurate and discrete to use Chinese code GB50936−2014 for predicting the bending bearing capacity of UFHST beams. Consequently, a new calculation method was proposed.