Research on fatigue performance and optimal design of steel-UHPC composite slab

Abstract

To study the crack resistance of UHPC (Ultra-High Performance Concrete) in the negative moment region of the steel-UHPC light composite bridge deck and the performance of fatigue-prone details around the arc-shaped notch, a full-scale two-span model with double U-ribs was fabricated according to the prototype of a steel box girder and subjected to six million fatigue load cycles. In parallel with the fatigue test, a numerical model (M1) was developed in ANSYS. Using the numerical model M1, three factors affecting the composite deck mechanical performance were analyzed, including the thickness of the UHPC layer, the amount of reinforcement placed in the UHPC layer, and the shear studs spacing. Combined with the reliability theory and Miner’s cumulative damage model, the fatigue reliability of the arc-shaped notch welding details was analyzed using another segmental numerical model (M2). The test results revealed no fatigue cracks around the arc-shaped notch of the diaphragm and the surface of UHPC layer after six million loading cycles. Furthermore, there was no delamination between the UHPC and the steel plate. The numerical simulation results indicate that the upper surface tensile stress for thin UHPC increases with the reduction in the shear studs spacing, however, there is an opposite trend for thicker UHPC. Moreover, the thicker the UHPC is, the more significant the influence of the reinforcement mesh spacing on the extreme tensile stress of the UHPC upper surface is. The calculation results of the segmental numerical model showed that the fatigue detail of the arc-shaped notch welded joints on the transverse rib (clear height of 0.9 m) base metal could not meet the design requirements. Based on the analysis of the relationship between the reliability index and UHPC thickness and the transverse rib clear height, it has been found that the detail of the arc-shaped notch welded joints on the transverse rib base metal could achieve infinite fatigue life without changing other design parameters except for the transverse rib clear height.