Experimental study on a novel method to improve progressive collapse resistance of RC frames using locally debonded rebars

Abstract

The alternate path (AP) method is widely used to evaluate the capability of reinforced concrete (RC) frame structures to resist progressive collapse. Previous studies have found that the double-span beam, caused by an internal column removal, fails to sufficiently develop catenary action due to strain concentration and premature fractures of longitudinal reinforcements near beam ends. To enhance catenary action, a novel method is proposed in this study by embedding locally debonded rebars at the half-height of beams near beam ends. For verification, five RC beam-column substructures were quasi-statically loaded representing an internal column removal scenario. Two test parameters were considered, i.e., the amount of additional rebars and whether they were debonded from the surrounding concrete. Test results found that the vertical resistance of the RC substructures using the proposed method increased by 66%–159% compared to that of conventionally designed substructure. The resistance of RC substructures using locally debonded rebars increased by 13%–21% compared to the substructures using an identical amount of bonded rebars. The reason for this resistance improvement is that the locally debonded rebars can improve both the ultimate rotation capacities of beam ends and axial tension forces in beams, resulting in sufficiently developing catenary action. In addition, the resistance contribution at the catenary action stage was identified and the lesser impact on the seismic performance of RC frame structures was discussed when using the proposed rebars. Finally, an analytical model was proposed to predict the ultimate rotation of beam ends and the ultimate resistance of RC substructures with locally debonded and bonded rebars.