Fatigue behavior of reinforced UHPC-NC composite beams

Ultra-high-performance concrete (UHPC) can be strategically applied in the lower part of a beam and combined with normal-strength concrete (NC) to achieve a more cost-effective design. The purpose of this research was to assess the effects of the UHPC layer thickness, reinforcement ratio, reinforcing bar type, and load level on the enhancement of the fatigue performance, as well as their interaction effects on the contribution of the UHPC layer. Four-point bending tests were conducted on eleven 500-mm-deep and 4400-mm-long T-beams under cyclic and monotonic loading. The test results indicated that the fatigue performance of the beam is strengthened by increasing the UHPC layer thickness, whereas the efficiency of the strengthening decreased as the thickness increased from 200 to 360 mm. The benefits of the UHPC layer on the fatigue resistance was magnified as the load levels decreased, which was also influenced by reinforcement ratio and reinforcing bar type. A method of deflection prediction was suggested, considering the contri-bution of the UHPC layer and effect of cyclic loading. Meanwhile, a fatigue relationship was established for reinforced UHPC-NC beams.