轻型组合桥面结构负弯矩区钢面板疲劳损伤演化机理与评估方法研究

The lightweight composite deck is a new bridge deck pattern consisting of an orthotropic steel deck and an ultra-high performance concrete (UHPC) layer. To develop a robust composite action at the steel-UHPC interface and therefore to reduce the stresses in both the steel deck and the UHPC layer, a large number of short headed studs should be welded to the deck plate. Welding of studs will influence the fatigue strength of the deck plate in negative moment zones, however, the mechanism of the influence is unknown because of the differences between the lightweight composite deck and conventional steel-concrete composite girders in terms of construction methods and mechanical behaviors. Thus, to reveal the fatigue-induced damage evolution mechanism of the deck plate in negative moment zones, the research program focuses on the following aspects: 1)the influence of the initial tensile stress on the fatigue performance of the deck plate welded with headed stud; 2) the influence of the shear stress range in the headed studs on the fatigue performance of the deck plate in the steel-UHPC composite deck; and 3)the fatigue evaluation method of the deck plate in the steel-UHPC lightweight composite deck. In research, the fatigue-induced damage evolution process and mechanism of the deck plate, caused by combined actions of initial tensile stress, shear stress range of the headed studs, and tensile stress range, will be revealed by means of fatigue tests, scanning electron microscope observations, and fracture mechanics analyses. In addition, hot-spot stress S-N curves can be established and a fatigue assessment method integrated with multi-scale FE calculation and hot-spot stress analysis can be developed. Based on the outcomes of the research, the knowledge of the fatigue performance of the deck plate in negative moment zones will be supplemented, producing a scientific basis for preventing the deck plate from fatigue cracking in service.

轻型组合桥面结构是一种新型桥面形式，由正交异性钢桥面板和薄层超高性能混凝土（UHPC）构成，两者通过焊接短栓钉牢固组合，以改善桥面受力。但大量焊接短栓钉会影响负弯矩区钢面板的疲劳强度，且因轻型组合桥面结构有别于常规组合梁的施工和受力特点，目前尚不明确具体的影响规律和机理。因此，为掌握短栓钉焊趾处钢面板的疲劳损伤演化机理，并为疲劳设计提供参考，本项目对以下内容进行研究：1）初始拉应力对带焊接短栓钉的钢板疲劳性能的影响机理；2）薄层UHPC中短栓钉剪应力幅对钢板疲劳性能的影响机理；3）轻型组合桥面结构负弯矩区钢面板的疲劳评估方法。研究中结合疲劳试验、扫描电镜观测、断裂力学仿真分析等方法揭示钢面板在复杂应力下的疲劳损伤演化过程与机理，建立热点应力S-N曲线，并将多尺度有限元计算与热点应力分析结合，建立疲劳评估方法。研究成果将扩充对负弯矩区钢面板的疲劳认知理论，为防止钢面板疲劳开裂提供科学依据。

轻型组合桥面结构由正交异性钢桥面板和薄层超高性能混凝土（UHPC）组合而成，以提高钢桥面的局部抗弯刚度，一体化解决钢桥面疲劳开裂、沥青铺装破损等难题。为了确保两者牢固组合，需在钢桥面上焊接大量短栓钉，导致轻型组合桥面结构的疲劳受力十分复杂。本项目通过理论和试验研究，探明了矮剪力键的传力机制，揭示了钢面板在复杂应力场下的疲劳损伤演化机理，构建了高效疲劳评估方法，具体如下：1）通过模型试验，探明了薄层UHPC中新型矮剪力键（超短栓钉、钢筋头等）在抗剪、抗拔、抗弯等典型荷载下的损伤特性和破坏模式，提出了抗剪承载力、荷载-滑移曲线、抗剪刚度计算理论和公式，明确了薄层UHPC中矮剪力键的设计方法；2）基于断裂力学理论，建立了钢面板受拉-短栓钉受剪耦合疲劳损伤演化计算框架，编制了疲劳裂纹扩展计算程序，结果表明，随着短栓钉剪应力幅的增加，钢面板200万次寿命的疲劳强度大致呈线性下降，建立了考虑两者耦合效应的疲劳强度计算公式，揭示了钢面板的拉-剪耦合疲劳损伤规律；3）探索了轻型组合桥面结构多尺度有限元建模方法，实现了计算效率和结果精度的平衡，对钢桥面、短栓钉和UHPC层进行了疲劳评估，结果表明，增设薄层UHPC后，钢桥面的疲劳应力降低约30~80%，基本消除了疲劳开裂风险，同时，论证了该结构各部位的抗疲劳安全性；4）以疲劳性能为主控目标，对轻型组合桥面结构进行了优化，一方面，对含大U肋的轻型组合桥面结构进行了疲劳评估，并通过足尺模型试验验证其优异的抗裂性，另一方面，通过计算明确了UHPC层厚、栓钉间距、横隔板厚等参数对轻型组合桥面结构疲劳寿命的影响规律，给出了关键参数建议取值。综合而言，本项目深入研究了轻型组合桥面结构的抗剪和抗疲劳性能，尤其是钢面板的拉-剪耦合疲劳损伤演化机理，完善了疲劳设计理论与评估方法，丰富了团队在该领域的系列研究成果，为相关技术标准编制和实桥工程应用提供了参考。