Towards enhancing the anti-progressive collapse performance of concrete beam-column structures via ECC and BFRP: Experiments and mechanisms

To investigate the beneficial effects of engineered cementitious composite (ECC) and basalt fiber reinforced polymer (BFRP) bars on the anti-progressive collapse robustness of concrete structures, three high-performance material composite specimens strengthened with ECC, hybrid reinforcements (BFRP bars and steel bars) or their combination and one ordinary concrete beam-column specimen were tested and simulated based on the pushdown method. Moreover, the influence relationships and improvement mechanisms of ECC, hybrid reinforcements, and their combination on structural robustness were revealed. The results demonstrated that all three composite specimens underwent typical flexural action (FA), compressive arch action (CAA), and catenary action (CA) stages and had enhanced capacities for structural dissipation of energy. In particular, their bearing capacity and ductility were dramatically distinguished from those of ordinary concrete structures. In comparison with the ordinary concrete specimen, ECC delayed the displacement of the initial fracture for longitudinal bars (33.7%) and the ultimate displacement (7.6%). The hybrid reinforcements with BFRP bars and steel bars increased the CAA capacity by 60% due to secondary stiffness action plus CAA mechanisms. More importantly, the combination of ECC and hybrid reinforcements exhibited a combined strengthening and toughening mechanism that resulted in a significant synergetic effect. The increase in the maximum load of the quasi-static or pseudo-static response owing to the combined strengthening and toughening mechanism surpassed the sum of individual load increase by the ECC and BFRP bars. Finally, based on the research findings, a design strategy for combining ECC (beam bottom) and hybrid reinforcements with BFRP bars and steel bars in a beam was recommended to enhance structural robustness.