Experimental study and calculation method on the flexural resistance of reinforced concrete beam strengthened using high strain‐hardening ultra high performance concrete

Abstract In this study, the efficiency of using high strain hardening ultra high performance concrete (HSH‐UHPC) on strengthening existing reinforced concrete beams was investigated by experimental and analytical means. First, the HSH‐UHPC constitutive relation was obtained using “Dog‐bone” specimen under uniaxial tensile test. Then three reinforced concrete beams strengthened with HSH‐UHPC layers and one control beam were tested under flexural loading. The midspan deflection, strain distribution, crack propagation and failure mode of the tested beams were described in detail. The tests verified that the middle section of UHPC‐NC composite beam basically conforms to the assumption of plane section. The flexural resistance of composite structure can be greatly improved by installing proper longitudinal reinforcement in UHPC layer. Meanwhile, numerical studies have been conducted on the tested beams using the experimentally obtained constitutive relations. The result shows that the finite element analysis results are consistent with the test results. Finally, a contribution factor for the HSH‐UHPC layer on the flexural resistance of the composite beam was proposed. At the same time, it is found that the contribution efficiency of the HSH‐UHPC to the flexural resistance increases with longitudinal reinforcement ratios in the HSH‐UHPC.