Axial compressive behavior of concrete-filled steel tubes with GFRP-confined UHPC cores

Abstract

The steel–concrete-GFRP-UHPC (SCGU) composite column is a new type of column consisting of steel, concrete, ultra-high performance concrete (UHPC) and glass fiber reinforced polymer (GFRP). The sectional form of the SCGU column is a circular steel tube as the outer layer, a GFRP-wrapped UHPC column as the core, and concrete between the core column and the steel tube. In this paper, axial compression tests were conducted on twenty-four SCGU composite columns, and their damage morphology, load–strain curves and influencing factors were analyzed. The results show that the damage modes of the specimens present multiple convex curves of the external steel tube, corresponding to the fragmentation of its plain internal concrete, the fracture of GFRP and the large axial crack of the UHPC core column; that the load–displacement curves of the composite columns can be roughly simplified to elastic, elastoplastic and plastic flow stages; that the composite columns still have high residual bearing capacity after compression damage; and that effect of tube thickness, number of GFRP layers and UHPC core column diameter of the specimen on the load bearing capacity and ductility of composite columns. Based on the mechanical analysis of each component of the SCGU composite column, a formula of axial compression bearing capacity of the SCGU composite column was presented, and agreement between the formula predicted results and the experimental results was obtained. In addition, finite element (FE) models that can simulate the SCGU composite column are developed.