Fatigue assessment of steel-UHPC composite deck with a thin polymer overlay in a long-span suspension bridge under static and random traffic loads

Steel-ultra-high performance concrete (UHPC) composite deck emerges as a novel structure that is promising to improve the fatigue performance of orthotropic steel deck (OSD). However, a long-span suspension bridge has a strict requirement on the self-weight of a steel-UHPC composite deck because it is susceptible to dead load variations. This study evaluates the fatigue performance of the steel-UHPC deck with a thin polymer overlay (TPO) in the Yichang Yangtze River Highway Bridge, a long-span suspension bridge, under static load and random traffic flow. The measured strains at the fatigue-prone details were employed to calculate the equivalent stress ranges and total fatigue life of the steel-UHPC deck. A three-dimensional finite element model was established and validated by experimental measurements to evaluate the steel-UHPC deck's stiffness and the TPO layer's crack resistance. The differences between the stress values predicted by the validated model and the experimentally measured ones were around 5%. The results showed that the steel-UHPC deck with TPO significantly reduced fatigue-prone details' equivalent stress ranges without increasing the dead load. The maximum stress reduction at various details reached 62%, and the total fatigue life at each detail in the steel-UHPC deck reached infinite life. The TPO layer has enough crack resistance in case the deck is overloaded by 50%. Compared with the original deck, the steel-UHPC composite deck improves the OSD's local stiffness and reduces relative deformation between structural components, thus reducing the stress ranges at fatigue-prone details and improving the bridge deck's fatigue performance. The results can provide a reference for the design and retrofit of the deck overlay of the long-span suspension bridge with OSD.