Diagonal cracking mechanism and reinforcement design method of bridge decks in cable-girder anchorage zone of composite girder cable-stayed bridge

In order to reveal the cracking mechanism of diagonal cracks in the cable-girder anchorage zone during the cantilever erection of a composite girder cable-stayed bridge, the distribution characteristics of shear stress and normal stress of bridge decks in the zone were analyzed starting from the actual stress state. The formation cause and morphological characteristics of the cracks were obtained in light of the stress Mohr's circle theory. Depending on the relevant codes and truss model, the measures against cracks through the design of diagonal reinforcement and L-shaped reinforcement were proposed. The Taizhou Bay Oversea Bridge was taken as an example to verify the stress distribution characteristics of the bridge decks in the anchorage zone and the effectiveness of the reinforcement methods. Research results show that the in-plane shear stresses of the bridge decks in the anchorage zone are mainly provided by the vertical and horizontal components of the cable force during the cantilever erection. The normal stresses in the longitudinal and transverse directions of the bridge are mainly provided by the overall bending moment of the cable-stayed bridge due to the load from the lifting weight, the local negative bending moment caused by the increase of the cable force, and the local pressure. Among these stresses, the increase of the normal stress in the longitudinal direction of the bridge is the main reason for the increase of the principal tensile stress in the cable-girder anchorage zone. When the principal tensile stress is greater than the tensile strength of the concrete, bridge decks have a great risk of diagonal cracking. Considering the effect of local pressure, cracks generally first appear at the top of bridge decks near the cable-girder anchor point. When gradually away from the anchorage zone, the influences of local negative bending moment and local pressure decreases, thus the normal stress at the top plate of bridge decks, and the principal tensile stress, and the included angle between the development direction of the crack and the longitudinal direction of the bridge becomes smaller gradually. At the same time, the normal stress of the bottom plate of bridge decks changes from compressive stress to tensile stress, and the principal tensile stress increases, which enhances the possibility of crack penetration. With the use of the truss model of diagonal cracking of concrete slab, the L-shaped crack-resistant reinforcement is deployed in the cable-girder anchorage zone. The maximum principal tensile stress of the top plate reduces by 1.26 MPa, in which the maximum normal stress in the longitudinal direction of the bridge reduces by 0.91 MPa, and the in-plane shear stress reduces by 0.50 MPa. Therefore, the crack-resistant reinforcement is capable of resisting bending and shear to some extent.