Behavior of GRAC-filled square steel tubular stub column under axial compression

Abstract

Geopolymer recycled aggregate concrete-filled steel tube (GRACFST) is a low-carbon and sustainable structural form. This paper conducted an experimental study on the mechanical behavior of square GRACFST stub columns under axial compression through twenty-two specimens' tests. The concrete type, strength grade, RA substitute rate, and steel tube thickness were considered as the main variables. The results indicated that the major failure mode of the columns is bulking failure, yet it can be alleviated by increasing RA substitute rates and steel tube thicknesses. Compared with cement-based RACFST, using geopolymer concrete leads to higher ultimate strength and initial stiffness of GRACFST, but lower ductility. While, the changing rule for the addition of RA is just on the contrary, with showing reduced ultimate load but improved ductility. The maximum reducing amplitude for ultimate load of GRACFST column is 16.34 %. Moreover, the thicker steel tube greatly enhances the ultimate load, stiffness and post-peak ductility, exhibiting prominent confinement effect on the core GRAC, which is insensitive to the concrete strength and RA substitute rate, but binder type. In addition, codes based on unified theory can provide accurate predictions for the ultimate resistance, and a simplified empirical calculation formula was developed based on test results. Furthermore, a theoretical calculation method using the multi-axial strength criteria of GRAC was proposed with showing improved prediction accuracy for the ultimate load-bearing capacity of GRACFST stub columns.