全体外预应力节段预制拼装连续梁桥承载能力足尺模型试验

芜湖长江公路二桥引桥首次采用了全体外预应力节段预制拼装连续梁桥，这一新型结构可采用工厂化预制，机械化安装，适应工业化建造，可显著提高建造效率，有效控制工程质量。为了对这种结构的受力性能进行全面研究，开展了全体外预应力节段拼装连续梁桥足尺模型试验。试验以背景工程5×40 m结构为原型，采用"1跨+1/3跨"的试验梁设计方案模拟连续梁特性。开展了施工全过程的同步测试，对梁体变形、结构应力和体外束应力变化进行了测试分析，并针对节段拼装连续梁的跨中断面开展了极限承载性能测试，分析了试验梁在极限破坏过程中变形、裂缝发展、体外束应力增量、主梁应力应变等结构响应。结果表明：采用"1跨+1/3跨"的设计方案能较好地反映连续梁的结构性能；施工过程中节段梁处于较好的弹性状态，跨内断面的纵向应力分布与体内束箱梁有很大区别，跨中断面纵向应力分布更为均匀；极限加载过程中，裂缝首先在弯矩最大断面附近接缝处出现，并形成一条主裂缝，沿着接缝逐渐向顶板发展，截面的受压区高度不断减小，结构的变形、顶板混凝土的压应力和体外束的应力也随之增大，最终因顶板混凝土压溃而丧失承载能力，试验梁实测承载能力为其设计承载能力的1.21倍；在极限加载过程中，体外预应力的最大增量为298 MPa。该新型结构的承载能力破坏过程为一个缓慢的延性变化过程，具有较好的安全储备，符合桥梁结构设计的要求。

Full-scale Test of Bearing Capacity of a Complete External Prestressed Segmental Precast Continuous Girder Bridge

For the first time, a complete external prestressed segmental precast continuous girder bridge is adopted in the approach spans of the second Wuhu Yangtze River highway bridge. This novel bridge type capitalizes on the factory prefabrication and mechanical assembly advantages, which are favorable for industrial construction. Furthermore, this bridge type can significantly enhance construction efficiency and is favorable for quality control. To investigate its structural behavior and mechanism comprehensively, a full-scale test of a complete external prestressed segmental precast continuous girder bridge was conducted. To model the realistic features of continuous girder bridges, the test employed a novel experimental scheme called "one span plus one-third span" based on a 5×40 m prototype. A synchronous experiment that dealt with the entire construction process was carried out in which the displacement, crack propagation, stress increment of the external prestress, strain, and stress of the girder were correspondingly measured and analyzed. The results indicate that the proposed novel experimental scheme of "one span plus one-third span" can reflect the structural features of continuous girder bridges accurately. The test girder was in the elastic state during the construction process, whereas the longitudinal stress distribution in the girder sections was different from that of the conventional internal prestressed box girders. Further, the longitudinal stress distribution in the middle section of the test girder was more even. During the ultimate loading processes, cracks occurred in the joint near the maximal bending moment, the main crack was subsequently formed, and the cracks propagated to the top plate. With the development of the cracks, the height of the compression zone of the section decreased, and the displacements of the girder, compressive stresses of the top plate, and stresses of the external prestresses gradually increased. Finally, the bearing capacity of the girder dramatically decreased with the crushing of concrete in the top plate. The test load-bearing capacity of the girder was 1.21 times that of its designed value. The maximal increment of the external prestress was 298 MPa. The full-scale test shows that this novel bridge type has a slow ductility-changing process in terms of failure of the load-bearing capacity, which proves that it has sufficient safety margin and meets the requirements of bridge design.