Comparative study on concrete-filled steel tube, FRP tube, and hybrid FRP-steel tube under the effect of eccentric loadings

The current paper consists of experimental and analytical phases. The experimental part investigates the behaviour of circular columns composed of concrete-filled steel tubes (CFST), concrete-filled CFRP tubes (CFFT), and Concrete-filled steel tubes wrapped externally with CFRP sheets in both longitudinal and hoop directions (CFCFST). A total of 15 columns were fabricated and tested up to failure under centric, eccentric, or beam loading conditions. The Experimental program consisted of three groups: each containing five specimens with the same cross-section type. However, each column in a group was tested under different eccentricities. The centrally loaded column in each group was designed to resist the same ultimate load. The failure mode, load-axial shortening, lateral confining strains, and moment-axial load interaction diagrams were observed. Results showed a general comparison between the overall behaviour for each cross-section type. An analytical calculation for the CFCFST moment-axial load interaction diagram is also presented. The experimental results showed that CFCFST columns could have been a better replacement for CFST columns. The proposed analytical calculations showed an applicable method for expecting the moment-axial load interaction diagram to be in good agreement with the experimental results.