Restrained shrinkage of ultra‐high performance concrete in bridge deck shear pockets and optimization of countermeasures

Abstract Ultra‐high performance concrete (UHPC) is widely utilized in shear pockets to form the shearing connection between steel girders and precast concrete decks. The restrained shrinkage of UHPC generates significant stress in the steel rebars, the clustered studs within the pocket, and the surrounding precast concrete, thereby altering the initial mechanical states of the bridge deck system. This motivates the investigation of the restrained shrinkage effect of UHPC in shear pockets and the structural optimization strategies to mitigate the induced stresses. Experimental measurements of restrained shrinkage in UHPC are compared with free‐stress shrinkage, revealing a 47% reduction in shrinkage strain at the pocket bottom compared to the latter one. The effect of the precast deck on the shrinkage strain is non‐uniform, with strains at the pocket center being 30% lower than those at the edges. Numerical reproduction of the restrained shrinkage of UHPC in the test provides detailed insights into the stress distributions in UHPC, steel rebars, clustered studs, and surrounding concrete. To mitigate the extreme tensile stress in shear pockets, two structural optimization strategies are evaluated. Among them, covering stud bodies with rubber hoses proves effective, reducing the extreme local tensile stress at the bottom corner of the shear pocket by 19%.