Experimental study on the ultimate bearing capacity of damaged RC arches strengthened with ultra-high performance concrete

•The crack distribution, hinge formation mechanism and bearing capacity of pre-damaged RC arches strengthened with UHPC were investigated.•The effects of the UHPC overlay on the strength, stiffness and ductility of damaged arches are analyzed.•Predictions of the ultimate bearing capacities of the damaged arches strengthened with UHPC are implemented. With the deterioration of the infrastructure and the increasing traffic volume, the service performance of bridge structures dramatically dropped. Strengthening and retrofitting these bridges with ultra-high-performance concrete (UHPC) can effectively improve their mechanical properties and durability. In this paper, the experimental investigation of the behavior of damaged RC arches strengthened with UHPC is presented. Three strengthened arches, including one arch strengthened with C50 (RC1-C50) and two arches strengthened with UHPC (RC2-UHPC, RC3-UHPC), were tested under asymmetric load. Load-deflection behavior, crack propagation pattern and hinge formation mechanism are extensively studied. Results indicated that the initial crack load and ultimate bearing capacity of composite arches strengthened by UHPC were respectively enhanced by 185% and 186%, showing good effects of strengthening and toughening on the original arch. On the premise of closing the cracks in the original arch ring, the stiffness and ductility of the composite arch strengthened with UHPC (RC2-UHPC) were improved by 58% and 34%, respectively. Different from the arch strengthened with C50 (RC1-C50), no obvious cracking and separation phenomena were observed in the interface of composite arches strengthened with UHPC in the whole process of eccentric loading. The combination of keyway and planting bar (rigid and flexible) can provide reliable bonding between the UHPC and the original structure. Finally, the calculation model for predicting the cracking load and ultimate capacity of the composite arches were proposed, and the calculation results are in good agreement with the experimental results.