Some recent results on the compressive and flexural behaviour of composite members

Experimental results from compression and flexural tests on steel tubular columns having circular or square or rectangular transverse cross-section and filled with plain or fiber reinforced concrete (FRC) are analyzed. For composite members different lengths and different dimensions of transverse cross-section were considered in order to assess their influence on behavior in flexure and in compression. The fibers investigated with different percentages were synthetic, carbon, and deformed steel fibers. The constituent materials were characterised through direct tensile tests on steel coupons and through compressive and split tension tests on concrete cylinders. Load-shortening and load-deflection curves were determined, including the softening response, in order to highlight the influence of the abovementioned parameters on the local and global effects related to second-order phenomena. Finally, simplified expressions for the calculus of the bearing capacity of composite members and load-deflection curves based on cross-section analysis are given. The experimental investigations presented here emphasize the beneficial effect due to the presence of concrete inside the tube: - in compression, better confinement effect in square and rectangular cross-sections and better post-peak behavior for slender columns in terms of axial compression; - in flexure, overstrength in shear and ductile flexural behavior.