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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 ¼-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. [ABSTRACT FROM AUTHOR]

A one-bay two-story reinforced concrete (RC) frame structure with weak beam-column joints was damaged during structural vibration control testing using a shake table. A damage assessment of the structure was conducted, and the structure was repaired using epoxy injection and retrofitted using basalt fiber-reinforced polymer (BFRP) sheets and retested. A seismic retrofit design method using fiber-reinforced polymer (FRP) for low-rise frame structures was proposed on the basis of mechanical analysis of the FRP-retrofitted structural components and the failure mode concept. The effective stiffness of each story increased notably after epoxy injection and FRP retrofitting. The shake table tests of the FRP-retrofitted structure showed that the shear capacity, ductility, and hysteretic energy dissipation capacity of each story were greatly improved and that the beam-column joint failure mode was prevented and the structure experienced much less damage compared with the original structure when subjected to ground motions of the same intensity. No debonding between the FRP sheets and the joints was observed after the shake table tests. [ABSTRACT FROM AUTHOR]