Improving Progressive Collapse Resistance of RC Beam-Column Subassemblages Using External Steel Cables

A retrofit method was proposed to improve the collapse resistance of RC frame structures by installing steel cables with preset lengths on the bottom of beams. The behavior of the structures remains unchanged under conventional loads with small deformations. This leads to the elimination of inconsistency (e.g., undesired failure mode) between conventional design and progressive collapse design for RC structures. To verify this retrofit method, five 1/4-scale beam-column subassemblages were statically tested under monotonic vertical loads representing an internal column-removal scenario. Experimental and analytical results found that the ultimate resistance of the retrofitted substructures improved by 90%-255% when two 10- or 14-mm diameter steel cables were used for beam-column subassemblages compared with the unretrofitted ones. In addition, preset cable lengths were determined based on deformation characteristics under conventional design and progressive collapse design. The ultimate resistance mechanism of retrofitted beam-column subassemblages was also revealed. Finally, a simplified model was proposed for the prediction of ultimate resistance of retrofitted RC beam-column subassemblages. (C) 2019 American Society of Civil Engineers.