Bond performance of novel NPR rebar-reinforced UHPC under cyclic loading

Abstract

Negative Poisson’s ratio (NPR) rebar, as a novel rebar, addresses the longstanding issue of enhanced strength leading to decreased ductility. In this paper, the bond behavior between NPR bars and ultra-high performance concrete (UHPC) under cyclic loading was investigated via eccentric pull-out tests. Utilizing the experiment results, considering the three parameters, two cyclic bond stress-slip τ–s constitutive models were developed on the basis of a monotonic τ–s constitutive model. The monotonic τ–s constitutive model was established based on artificial neural network (ANN). The test results showed that under cyclic loading, the bond energy dissipation capacities of the specimens with different types of rebar followed the order of NPR>HRB635 >HRB400 >HG. The specimens with NPR rebar exhibited a higher energy dissipation capacity and less bond strength degradation than other rebar-reinforced specimens, making NPR rebar more suitable for use under cyclic loading. From the perspective of bond behavior and energy dissipation, fiber reinforcement could not effectively replace stirrup reinforcement. Hence, when designing NPR rebar-reinforced UHPC structural components, it is recommended to use an appropriate stirrup ratio to ensure that the structural components meet the energy dissipation requirements to satisfy seismic demands. The proposed τ–s constitutive model could accurately predict the bond behavior between NPR bars and UHPC under cyclic loading. Specifically, Model 2 was suitable under various bond lengths, while Model 1 was applicable only when l_d≥ 3d. Moreover, the accuracy of Mo_del 2 is greater than that of Model 1.