Tests of concrete-filled double skin (SHS outer and CHS inner) composite stub columns

Abstract

This chapter describes a series of compression tests carried out on concrete filled double skin tubes (CFDST). The outer tube is made of square hollow sections (SHS), while the inner skin is made of circular hollow sections (CHS). The failure mode, strength, ductility, and energy absorption of CFDST are compared with those of empty single skin tubes. Concrete-filled double skin tubes (CFDST) consist of two concentric steel cylinders or boxes with the annulus between them filled with concrete. This form of construction can be applied to seabed vessels, in the legs of offshore platforms in deep water, to large diameter columns, and to structures subjected to ice loading. Theoretical models are developed to predict the ultimate strength of CFDST stub columns. Increased ductility and energy absorption is observed for CFDST stub columns especially for slender outer tubes. Four section sizes are chosen for the outer tubes with width-to-thickness ratio ranging from 17 to 50. Some sections are fully effective while some sections are not fully effective (that is, full section yielding cannot be achieved in compression due to local buckling) in order to investigate the effect of width-to-thickness ratio on the behavior of double skin composite stub columns.