Experimental investigation on the progressive collapse resistance of UHPC-RC composite beam-column structures

An innovative technique for enhancing the structural anti-progressive collapse performance was proposed by utilizing ultra-high-performance concrete (UHPC) in reinforced concrete (RC) structures. To this end, three UHPC-RC specimens with different UHPC application locations or thicknesses and one RC specimen were tested based on an alternative path method to investigate the improvement effect and mechanical mechanism of UHPC. The experiments demonstrated that the UHPC-RC structures experienced three resistance mechanisms, including flexural action (FA), compressive arch action (CAA), and catenary action (CA). Moreover, UHPC at the beam top or bottom significantly improved the FA and CAA capacities. UHPC at the beam top delayed the first rupture of steel bars. Additionally, the numerical simulation was performed for eight UHPC-RC specimens, and the influ-ence of UHPC location and thickness on structural robustness is further discussed. Based on the experimental and numerical results, seven enhancing mechanisms by UHPC are revealed, namely ultra-high compressive strength, good tensile properties, excellent toughness, large elastic modulus, fine and dense multi-slit cracking charac-teristics, interface constraint effect on cracks, and passive confinement effect on ordinary concrete. Finally, based on the research findings, the suggestion that UHPC at the beam bottom (not more than 40% of the beam height) is superior to that at the beam top for the improvement of structural robustness is propounded.