Development of compressive arch action in reinforced concrete sub-assemblages

Compressive arch action (CAA) of reinforced concrete (RC) members is a beneficial structural mechanism to mitigate progressive collapse of RC framed structures without any additional cost. CAA relies on the restraints at the ends of RC beams that are provided by surrounding structures as well as the material and geometric properties of RC beams. An analytical model is utilized to perform detailed parametric investigation into the effects of imperfect boundary conditions on the CAA capacities of sub-assemblages. The results indicate that to mobilize CAA, adequate axial and rotational restraints must be provided, but when restraint stiffnesses are respectively greater than the corresponding stiffness of restrained beams, the effects of restraint stiffnesses on CAA capacity are negligible. Then, the effects of span-to-depth ratios and mechanical reinforcement ratios of beams on enhancement of structural resistance due to CAA are investigated. The results suggest that a lower mechanical reinforcement ratio and a lower span-to-depth ratio will give rise to significant enhancement of structural resistance contributed by CAA