Study on mechanical behavior of reinforced concrete (RC) beams strengthened with ultra-high performance concrete (UHPC)

Abstract

The mechanical characteristics and the calculation method for the normal section bearing capacity of reinforced concrete (RC) beams strengthened with ultra-high performance concrete (UHPC) were investigated. The effects of the reinforcement ratio and UHPC layer thickness on the mechanical performance of UHPC-NC beams were experimentally studied. Based on theoretical analysis combined with experimental findings, a new calculation model for the normal section bearing capacity of UHPC-strengthened beams was proposed. Validation with experimental data indicates that the proposed model possesses high accuracy and versatility. Furthermore, based on experimental and simulation analyses, the cross-sectional stress redistribution laws of RC beams under load during the strengthening process, as well as the subsequent resistance performance of such beams after strengthening, were explored. The results show that strengthening damaged RC beams in the tension zone with UHPC can significantly improve the normal section bearing capacity, stiffness, and cracking resistance of the beams, although the ductility is somewhat reduced. During the strengthening of loaded RC beams, continuous redistribution of cross-sectional stresses occurs. The maximum compressive strain, neutral axis height, deflection, and crack width of the cross-section all exhibit an initial increase followed by a decrease, with the maximum variation in deflection reaching up to 20%. After the loaded RC beams are strengthened and reach the ultimate limit state of bearing capacity, the tensile contribution of the UHPC layer can be fully utilized. The bearing capacity is comparable to that of beams strengthened without prior loading.