Fatigue Assessment of Retrofitted Bridge Welds in the High Cycle Domain

最近的报告量化了桥梁业主面临的重大维护成本，从安大略省的22亿美元到美国整个桥梁存量的1400亿美元不等。为了最大限度地降低这些成本，正在开发新的改造方法来延长桥梁的使用寿命，包括：使用疲劳性能增强焊后处理，用纤维增强聚合物（FRP）材料加固，以及使用铝等轻质材料更换桥面。在评估这些改装方法的耐久性时，疲劳仍然是一个核心问题。为了使这些方法在常规基础上安全实施，需要进一步研究：1）验证其在使用中变幅（VA）负载条件下的长期性能，2）开发改进的预测模型，以了解行为并促进最佳改造规划和设计。 为了满足这一需求，计划对改装桥梁焊缝的疲劳性能进行基础研究，项目重点是上述每种改装方法。采用的研究方法包括：小规模改装焊接试样的快速疲劳测试（频率高达100 Hz），大型改装接头试样的疲劳测试，使用先进技术（数字成像，交流电位降）的裂纹扩展监测，以及非线性（基于应变）断裂力学分析。根据这项基础研究的结果，还将开发简化的预测模型。 计划中的研究将是原创的，因为它将回答有关高循环域VA加载条件下改装焊缝疲劳行为的重要问题，并采用相对新颖和复杂的测试和分析方法。通过这项研究获得的知识将导致与金属桥梁维护相关的生命周期成本显着降低，通过延长使用寿命，提高结构安全性，并降低改造成本。此外，四名研究生（两名博士）和两个硕士）将得到支持和培训，作为所要求的资金的结果。

Recent reports have quantified the significant maintenance costs facing bridge owners, with numbers ranging from $2.2 billion for the Province of Ontario to $140 billion for the entire bridge stock in the US. In order to minimize these costs, new retrofitting methods are being developed for extending the service lives of bridges, including: the use of fatigue performance enhancing post-weld treatments, strengthening with fibre-reinforced polymer (FRP) materials, and deck replacement using lighter materials such as aluminum. In assessing the durability of these retrofitting methods, fatigue remains a central issue. For these methods to be safely implemented on a routine basis, there is a need for further research to: 1) verify their long term performance under in-service variable amplitude (VA) loading conditions, and 2) develop improved predictive models to gain insight regarding behaviour and facilitate optimal retrofit planning and design. To address this need, fundamental research on the fatigue behaviour of retrofitted bridge welds is planned, with projects focusing on each of the above-mentioned retrofitting methods. The research methods to be employed include: rapid fatigue testing (at frequencies up to 100 Hz) of small-scale retrofitted weld specimens, fatigue testing of larger retrofitted joint specimens, crack growth monitoring using advanced techniques (digital imaging, AC potential drop), and nonlinear (strain-based) fracture mechanics analysis. Simplified predictive models will also be developed, based on the results of this fundamental research. The planned research will be original in that it will answer important questions regarding the fatigue behaviour of retrofitted welds under VA loading conditions in the high cycle domain and employ relatively novel and sophisticated testing and analytical methods. The knowledge obtained through this research will lead to significant reductions in the life-cycle costs associated with the maintenance of metal bridges through service life extension, increased structural safety, and reduced retrofit costs. In addition, four graduate students (two Ph.D. and two Master's) will be supported and trained as a result of the requested funds.