全预制轻型预应力UHPC薄壁盖梁抗剪性能试验

为解决桥梁装配式施工中传统混凝土盖梁自重过大、整体吊装困难的难题，提出全预制轻型部分预应力超高性能混凝土（Ultra-high-performance Concrete，UHPC）薄壁盖梁的设计方案。为研究UHPC薄壁盖梁的斜截面抗裂性能及抗剪承载力，完成1根相似比1：2的大比例UHPC薄壁盖梁共2次模型试验，获得模型从加载到破坏全过程的开裂和破坏荷载、裂缝和变形分布规律等关键试验结果；分析梁体应变、预应力、裂缝的分布规律，考虑UHPC的应变硬化特征，基于材料力学公式提出斜截面开裂剪力的理论计算方法，考虑UHPC结构裂缝分布和结构形状系数等，提出斜裂缝宽度的计算公式。按照不同规范对UHPC盖梁抗剪承载力进行计算对比，以法国UHPC规范为基础，对比分析UHPC基体、箍筋、钢纤维及纵筋销栓作用对结构抗剪承载能力的影响程度。研究结果表明：计算结果与模型的开裂剪力以及裂缝宽度吻合良好；各国规范均低估了UHPC结构的抗剪承载能力；提出的UHPC盖梁具有自重轻、施工快捷等特点，充分利用了UHPC的超高抗拉性能和应变硬化特征，具有优异的斜截面抗裂性能以及抗剪性能；建议取消弯起钢筋、适当增加预应力筋，浇筑UHPC时应增设抗浮措施等。研究成果可为UHPC盖梁的应用提供参考。

Experimental on Shear Behavior of Prefabricated Light Weight Thin-walled UHPC Bent Cap

To solve the problem of excessive self-weight and overall lifting of conventional concrete bent caps in bridge prefabricated construction, a design scheme of fully prefabricated lightweight, thin-walled prestressed UHPC bent cap was proposed. To study the crack resistance and shear capacity of the diagonal section of the UHPC bent cap, two model tests were conducted on a large-scale UHPC lightweight, thin-walled UHPC bent cap with a similar ratio of 1:2. Key test results were obtained for the entire process, such as cracking and failure loads, and distribution of cracks and deformation. In addition, the distribution properties of strain, prestress change and crack development are analyzed. Considering the strain hardening characteristics of UHPC, a theoretical method for calculating the shear force for cracking of the diagonal section was proposed based on material mechanics formula.Considering the crack distribution and shape coefficient of the UHPC structure, a formula for calculating the oblique crack width was proposed.The shear capacities of the UHPC cover beams were calculated and compared according to various codes. The results show that the shear capacity of UHPC structures is underestimated in the codes of different countries. The calculation results are consistent with the values of shear force for cracking and the crack width of the model. Based on the French UHPC code, the degree of influence of the shear capacity of the structure under the action of UHPC, stirrups, steel fibers, and dowel action was analyzed. The results of the test and analysis show that the UHPC bent cap proposed in this paper has the characteristics of low self-weight and quick construction;further, this design fully uses the ultra-high tensile properties and strain hardening characteristics of UHPC. The UHPC bent cap also has good oblique section cracking behavior and shear behavior. It is recommended to eliminate the bending of the steel bars, increase the prestressing tendons properly, and add anti-floating measures while pouring the UHPC. The research results presented in this paper can provide reference for various applications of UHPC bent caps.