Fatigue performance and residual capacity of UHPC-reinforced simply supported-to-continuous concrete box beams in negative moment zone: experimental study

ABSTRACT This study investigated the effects of reinforcement ratio and fatigue load level on the fatigue performance and residual capacity of ultra-high performance concrete (UHPC) continuous box beams in the negative moment region. Six UHPC specimens were designed and fabricated, with some tested statically and others subjected to fatigue loading. The research specifically examined how reinforcement ratio and fatigue loading influence structural performance parameters, including mid-span deflection and reinforcement strain, during fatigue testing. And the accuracy of the experimental results was further verified through finite element numerical simulations. The experimental results demonstrated that: During static loading tests, beams B1 and B2 demonstrated an increase in flexural capacity of 8% and 25%, respectively, relative to the reference beam B0. These findings indicate that the application of UHPC in the negative moment region of simply supported-to-continuous box beams significantly enhances flexural performance. This enhancement is attributed to optimized stress distribution within the cross-section, which improves ductility and damage tolerance. Following 2 million fatigue cycles, no observable fatigue damage was detected in beams PLB0, PLB1, or PLB2. Post-fatigue static failure tests were subsequently conducted on these beams. Compared to their corresponding reference beams (B0, B1, B2), PLB0, PLB1, and PLB2 exhibited reductions in maximum mid-span deflection of 30%, 16.1%, and 5.8%, respectively, along with markedly lower reinforcement stress amplitudes. Beam PLB0 exhibited a 10% reduction in residual capacity relative to the static ultimate capacity of reference beam B0. Conversely, beams PLB1 and PLB2 demonstrated residual capacity increases of 4% and 21%, respectively, surpassing the static ultimate capacity of their corresponding reference beams (B1 and B2). These findings demonstrate that UHPC implementation enhances flexural stiffness, retards fatigue damage accumulation, and effectively increases residual capacity in bridge components.