Pre-relaxed cables for improving progressive collapse resistance of RC frame subassemblages considering slabs

Abstract

A common method to improve the progressive collapse resistance of reinforced concrete (RC) frame structures is to increase the reinforcements in beams, which might result in the undesired failure mode of strong beam-weak column for the structures under earthquakes. To improve the progressive collapse resistance of the RC frame structures without affecting their seismic behaviors, a novel retrofit has been proposed using pre-relaxed cables. This study investigated the improvement of the pre-relaxed cables on the progressive collapse resistance of the RC frame structures considering the presence of the slabs subjected to the distributed loads. A quasi-static test was carried out on two one-quarter scaled 2 × 2-bay subassemblages, i.e., a beam-slab (BS) subassemblage and a beam-slab-cable (BS-cable) subassemblage. Experimental results found that the progressive collapse resistance and deformation capacity of the BS-cable subassemblage was 55 % and 260 % larger than those of the BS subassemblage, respectively. The resistance improvement mechanism of the BS-cable subassemblages was revealed, i.e., the tensile catenary action in the beams, tensile membrane action in the slabs, and tension action in the cables. The finite element (FE) models were then developed, validated against the experimental results, and used for parametric studies with the consideration of the cable diameter and cable original length. Numerical results found that there were two failure modes for the BS-cable subassemblages, i.e., beam failure mode and slab failure mode. The upper limit of the improvement of the progressive collapse resistance using the cables is critically related to the failure mode. For the beam failure mode, the increase in the cable diameter could improve the progressive collapse resistance until the slab failure mode occurred.