Investigation on cracking performance of UHPC overlaid concrete deck at hogging moment zone of steel-concrete composite girders

: The concrete deck at the negative bending moment region of a continuous steel-concrete compositegirderbridgeistheweakestpartofthestructure.Introducingultra-highperformanceconcrete (UHPC) to the hogging region may overcome the shortage and break through the bottleneck. This paper explores the cracking performance of steel-concrete composite girders with concrete slabs topped by athinlayerofUHPCsubjectedtoanegativebendingmoment.Arealcontinuouscompositegirderbridge is briefly introduced as the engineering background, and the cracking characteristic of the concrete deck over the middle piers of the bridge is numerically modeled. Approaches to strengthen the cracking performance of the concrete deck at the hogging region through topping UHPC overlays are proposed. The effectiveness of the approaches is examined by conducting a series of numerical and experimental tests. Numerical results indicate that the normal concrete (NC) deck near the middle forums of the bridge would crack due to the large tensile stress from negative bending moments. Replacing the top concrete withan identical-thick UHPCoverlay can increasethe cracking resistanceof the deckunder the moment. As the thickness of the UHPC overlay increased from 6.0 cm to 12.0 cm, the maximum shear stress at the UHPC overlay-to-NC substrate interface under different load combinations was decreased by 56.3% ∼ 65.3%. Experimental results show that the first-cracking load of the composite beam using