钢-UHPC轻型组合梁桥负弯矩区桥面板抗裂性能强化机理及裂缝宽度计算方法

Conventional steel-concrete composite beam is wildly used because it can take fully advantage of material properties of both steel and concrete with efficiency and economy. However, the massive self-weight of normal concrete limits its application to long-span bridge structures, and the insufficient crack resistance of concrete deck in negative moment zones also threatens the durability of the composite structure. Based on the ultra-high performance concrete (UHPC), the applicant has proposed a steel-UHPC lightweight composite beam, which can significantly reduce the self-weight of the composite structure. But, the crack resistance of the UHPC deck will challenge the successful application of the steel-UHPC lightweight composite beams. Therefore, this research will focus on the crack resistance strengthening and crack evolution mechanism of UHPC deck of lightweight composite beams in negative moment zones. The research will carried out in the following three successive stages: (1) the influence of fiber hybridization on crack resistance of UHPC, and the tensile constitutive relationship involving a part of stress-crack width curve for UHPC; (2) the crack resistance enhancement and crack propagation mechanism of the lightweight composite beam, and the related calculation method for crack width; (3) reasonable configurations for the negative moment zones of steel-UHPC lightweight composite beam. By means of bending tests, FEM simulation, and fracture mechanics analyses, the knowledge of the crack evolution of UHPC deck of composite beam in negative moment zones will be broaden. The research in the project will provide the useful reference for the applications of the steel-UHPC lightweight composite beam to bridge engineering.

传统钢-混凝土组合梁能充分发挥钢和混凝土材料的优势，经济性较好。但应用于大跨径桥梁面临自重大的难题，同时负弯矩区混凝土桥面板易开裂，影响结构耐久性。申请者利用超高性能混凝土（UHPC）材料研发的钢-UHPC轻型组合梁，可大幅减轻梁体自重，但桥面板抗裂性能不足的难题仍需解决。因此，本项目将围绕钢-UHPC轻型组合梁桥负弯矩区桥面板抗裂性能强化机制和裂缝演化机理，开展以下基础性研究：1)探明混合纤维对UHPC材料拉伸抗裂性能的影响机理，建立含裂后应力-裂缝宽度曲线的UHPC材料拉伸本构关系；2)揭示钢-UHPC组合梁负弯矩区抗裂性能强化及裂缝演化机理，建立相应的裂缝宽度计算方法；3)提出适用于钢-UHPC轻型组合梁桥负弯矩区的合理构造形式。研究将结合静力试验、有限元仿真和断裂力学分析等手段，扩充轻型组合梁负弯矩区桥面板的裂缝演化认知，研究成果将为钢-UHPC轻型组合梁的工程应用奠定坚实的基础。

近年来钢桥建设进入快速发展期，主要桥型之一的钢混组合桥梁面临自重大和混凝土桥面板易开裂的难题，难以适用于大跨径桥梁结构。钢-UHPC组合梁桥有望突破上述技术瓶颈，但负弯矩区UHPC桥面板抗裂性能强化已成为大跨径桥梁研究领域无法回避的新问题。针对上述问题，本项目首先通过平直型和端钩型钢纤维UHPC拉拔试验，分析钢纤维混杂配比、体积掺量对钢纤维-UHPC界面黏结性能的影响，建立两类钢纤维拔出过程的黏结–滑移模型，研究表明平直型和端钩型钢纤维体积掺量均为1%时，混杂钢纤维的界面黏结增强效果最佳。研究配筋-UHPC界面的黏结性能，选取钢筋直径、黏结长度和保护层厚度为变量设计配筋UHPC拉拔试验，探究其对界面极限黏结强度、黏结-滑移关系及破坏模式的影响，结果表明配筋黏结长度和保护层厚度可大幅降低，构建轻型薄壁UHPC结构。提出钢筋与混杂钢纤维增强UHPC(R-UHPC)，以钢纤维掺量和配筋率为变量设计R-UHPC拉伸试验，基于R-UHPC拉伸抗裂性能强化目标，定量分析各参数对R-UHPC试件拉伸性能的影响，研究表明随钢筋配筋率增加，R-UHPC构件的抗拉强度、硬化刚度、可视初裂应力、极限应变、UHPC自身应变硬化能力和峰值后延性均显著增长，宏观裂缝数目增多而裂缝间距减小，破坏模式从单缝转为多缝破坏，提升R-UHPC构件配筋率以降低钢纤维掺量或强化抗拉性能是技术经济合理的，可实现大跨UHPC桥梁的抗裂性能强化。以配筋率为变量设计配筋UHPC梁纵向受弯试验，考虑收缩徐变、UHPC抗拉贡献、配筋粘结滑移及受拉刚化效应等因素，提出R-UHPC受弯梁非线性简化分析模型，并建立R-UHPC受弯构件挠度及裂缝宽度计算方法，基于简化模型计算值与试验结果比较分析，简化非线性分析模型计算精度高，可有效预测R-UHPC受弯试验梁的挠度及裂缝宽度，有望为钢-UHPC组合梁负弯矩区桥面板裂缝宽度计算提供参考。