预制小箱梁纵向U筋交错搭接接缝静载试验

预制小箱梁因其结构可靠和施工方便得到了广泛应用。传统的小箱梁纵向接缝工艺采用环形套箍将相邻桥面板翼缘内预留的外伸U筋焊接起来，这种焊接工艺使得湿接缝能很好地传递弯矩和剪力。但这种工艺对梁体的定位精度要求高，现场焊接工作量大，且存在潜在的钢筋疲劳问题，不利于桥梁快速施工。为加速桥梁施工，针对预制小箱梁的纵向湿接缝，提出采用U筋交错搭接方式来改善传统的环形套箍焊接连接。通过制作24个足尺试验模型进行静载试验，分析各试件的破坏形态、抗弯能力和开裂性能，研究U筋交错搭接接缝的性能，并对2种不同的接缝形式进行对比。研究接缝区混凝土强度、U筋纵向间距、搭接长度、U筋直径、板厚和接缝宽度6个设计参数对U筋交错搭接接缝受力性能的影响，并提出了相应的设计建议。研究结果表明：相同配筋率下的采用U筋交错搭接接缝和传统焊接接缝的板承载能力基本相同，但是U筋交错搭接接缝开裂更早且裂缝发展更快，不过仍然满足规范的最大容许裂缝宽度要求；受分阶段施工的影响，混凝土首先在接缝结合面处开裂；控制U筋搭接角度小于45°可以保证接缝不发生脆性破坏；U筋纵向间距、U筋直径、板厚和接缝宽度对接缝受力性能影响较大。

Static Loading Test of Longitudinal Joint Details Using Staggered U-bars in Precast Multibox Girder Bridges

Precast multibox girders have been widely used owing to their reliable structure and convenience in terms of construction. The traditional longitudinal joint uses a big hook to weld the extended U-bars, which are pre-embedded in the flanges of adjacent bridge decks. This type of longitudinal joint can well transfer shear and bending moment from one girder to the adjacent girders. However, this process requires high positioning accuracy of the beam body and large amount of field welding work, in addition to potential occurrence of reinforcement fatigue problems, which are not conducive to rapid bridge construction. To accelerate bridge construction, longitudinal joint details with staggered U-bars were proposed to connect adjacent precast box girders and replace the traditional welded-loop details. Twenty-four full-scale specimens were fabricated, and static loading tests were conducted to investigate the failure mode, flexural strength, and cracking behavior of all specimens. The performance of the specimens with welded-loop and U-bar details was compared. The influence of the joint concrete strength, U-bar longitudinal spacing, U-bar lap length, U-bar diameter, slab thickness, and joint width on the joint performance was investigated, and corresponding design suggestions were proposed. The test results show that although the specimen with U-bar detail has the same load-carrying capacity as that of the specimen with welded-loop details under the same reinforcement ratio, it cracks sooner and faster; however, it still satisfies the code requirement in terms of maximum allowable crack width. Cracks first occur at the joint interface due to the construction sequence. Controlling the lap angle of the U-bars to less than 45° can prevent brittle failure of the joints. The U-bar longitudinal spacing, U-bar diameter, slab thickness, and joint width significantly influence the joint performance.