组合梁斜拉桥索梁锚固区桥面板斜向开裂机理与配筋设计方法

为揭示组合梁斜拉桥在悬拼施工时，索梁锚固区斜向裂缝的开裂机理，从实际受力状态出发，分析了该区域桥面板剪应力和正应力的分布特点，并结合应力莫尔圆理论给出了裂缝成因及其形态特征；基于相关规范及桁架模型，提出了斜向配筋和L形配筋设计的抗裂措施；通过台州湾跨海大桥实例分析，验证了锚固区桥面板的应力分布特点与配筋方法的有效性。研究结果表明：悬拼施工时，锚固区桥面板的面内剪应力主要由拉索索力的竖向分力和水平分力提供，纵、横桥向正应力主要由吊重荷载引起的斜拉桥整体弯矩、拉索索力增加引起的局部负弯矩和局部承压提供；纵桥向正应力的增加是引起索梁锚固区主拉应力变大的主要原因，当主拉应力大于混凝土抗拉强度时，桥面板存在较大的斜向开裂风险；考虑到局部承压的作用，裂缝一般首先出现在索梁锚固点附近的桥面板顶部；当逐渐远离锚固区时，局部负弯矩及局部承压影响减小，桥面板顶板正应力减小，主拉应力减小，裂缝的发展方向与纵桥向夹角逐渐减小，同时，桥面板底板正应力由压应力变成拉应力，主拉应力增大，裂缝产生贯通的可能性增大；基于混凝土板斜向开裂的桁架模型，对索梁锚固区配置L形抗裂钢筋，顶板最大主拉应力降低了1.26 MPa，其中，纵桥向正应力最大可减小0.91 MPa，面内剪应力可减小0.50 MPa，即配置抗裂钢筋能够达到一定的抗弯和抗剪的效果。

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.