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.

The Prediction of Cracking Load and Peak Load of UHPC‐NC Composite Structure

“…Some of the calculation results are closer to the experimental data than the original calculation models. Especially in the calculation of reference [19], there is a big gap between the original calculation results and the experimental values, but the calculation results in this paper are very close to the experimental values. Terefore, this model can calculate the peak load more accurately than other calculation models.…”

“…Te defection, strain distribution, crack propagation, and failure mode are described in detail. Te tests verifed that the middle section of the UHPC-NC composite beam conforms to the assumption of the plane section [19].…”

“…In reference [18], steel bars are added to ordinary reinforced concrete and UHPC. In reference [19], the UHPC layer has prestressed tendons. Te calculation shows that the cracking load calculated in this paper is very close to the experimental cracking load in references [12,18,19], so the model in this paper is suitable for UHPC with and without reinforcement [18,24,25].…”

“…Te experiments in the literature prove that the junction between UHPC and NC is well connected and can be regarded as the same cross-section [18][19][20][21]. So, all calculation models follow the assumption of the plane section even at the junction of UHPC and NC.…”

“…By adding the UHPC layer on the tensile side, the stifness can be greatly improved, the formation of cracks was delayed, and the peak load was slightly increased [22]. Te experimental results of reference [13] show that the fexural resistance of UHPC-NC can be greatly improved by installing proper longitudinal reinforcement in the UHPC layer [19].…”