Behavior of steel-ECC composite bridges under post-fire conditions

To solve the issue of cracking on the concrete slab, engineered cementitious composite (ECC) has been applied to steel-concrete composite bridges. However, few studies have been conducted on their behavior under post-fire conditions. In this study, experimental and numerical research on the steel-ECC composite bridge girders after elevated temperatures and different cooling methods are presented. The same testing conditions were used to evaluate the material properties of ECC, Q345 steel, and HRB400 rebars. Then, heating tests and loading tests were conducted sequentially on the steel-ECC composite bridge girders. Relevant thermal and structural responses, including heat transfer, load-deflection curves, failure modes, and strain distribution, were recorded. At last, a numerical model was validated with test data and utilized to further investigate the effect of fire load scenarios. Results from experiments indicated that cooling methods had a significant influence on the performance of ECC. Water cooling intensified the hydration reaction of ECC when heating up to 400 °C, thereby reducing the compressive strength. The width of cracks on the ECC slab was found to extend after water cooling. When heated up to 400 °C, the residual bearing capacity of composite girders reduced to 91.58% and 74.29% with natural cooling and water cooling, respectively. Moreover, numerical studies pointed out that fire load on the ECC slab rather than under the steel girder caused more damage to the steel-ECC bridges.