Experimental and theoretical analyses of the progressive collapse resistance of NSM strengthening RC frames after the failure of a corner column

When exposed to accidental loads, reinforced concrete (RC) frames are vulnerable to progressive collapse after the failure of a corner column, so necessary strengthening schemes should be employed for the frame. By strengthening the slab with near-surface-mounted (NSM) glass fiber-reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) layer, this study experimentally revealed the effect of the strengthening method on the progressive collapse behavior of beam-slab systems after the removal of a corner column. Then, on the basis of experimental results, a theoretical analysis method of the peak capacity for the beam-slab system is proposed according to the principle of virtual work and the yield-line theory. The derived formula can accurately predict the progressive collapse resistance of the RC beam-slab system after the failure of a corner column and quantitatively evaluate the contribution of floor slabs to the structural capacity. The validity of the method is also proven by the application to the structural capacity of a flat-slab system and a beam-column system. Finally, according to the theoretical formula, the influence of several parameters on the structural capacity is investigated, such as the earthquake fortification intensity of the frame, the over-strength factors, the column spacing, and the depth-to-span ratio of the beam. The research results demonstrate that after considering the L-beam action, the capacities of the test specimens can be improved by 52%–65%. The capacity of the flat-slab system is the lowest among the above three structural systems. The structural progressive collapse resistance can be effectively improved through enhancing the constraint stiffness of the corner beam-column joint and utilizing building materials with high plastic development ability.