Strength and ductility of concrete filled double skin (SHS inner and SHS outer) tubes

This paper describes a series of compression and bending tests carried out on concrete filled double skin tubes (CFDST). Theoretical models developed to predict the ultimate strength of CFDST stub columns and beams are also described. Both outer and inner tubes were cold-formed C450 (450 MPa nominal yield stress) square hollow sections (SHS). Four different section sizes were chosen for the outer tubes with a width-to-thickness ratio ranging from 16.7 to 25.0. One section size was chosen for the inner tube which had a width-to-thickness ratio of 20. It was found that there is an increase in ductility for CFDST both in compression and bending when compared to empty single skin tubes. It was also shown there was good agreement between theoretical and experimental results.