Ultimate and permissible limit state behaviour of soil-filled masonry arch bridges

在英国的公路和铁路网上，大约有70,000座石拱桥跨度(约全球跨度为100万跨度)，其中绝大多数跨度已远远超过桥梁通常预期的120年寿命。尽管砖石拱桥通常被认为是寿命长的结构，但现在有大量的桥梁出现了破损的迹象。然而，仅在英国更换这些桥梁的成本就高达数百亿英镑，它们的美学和遗产价值也是巨大的。遗憾的是，目前用于评估其能力的方法已经过时和/或过于简单化，这使得确定更新或翻新计划的优先次序的任务变得极其困难(仍广泛使用的可追溯到1940年代的MEXE评估方法预测能力非常有限，而且没有提供未来改进的余地)。风化、不断增加的交通量，以及气候变化(影响水上桥梁)带来的洪水事件增加等因素，只会加剧这种情况。此外，尽管最近研究的主要重点是结构失效的预测(“极限状态”)，但预测发生递增破坏的服务负荷水平(“允许的极限状态”)现在是基础设施所有者的一个关键优先事项，他们面临着提供有弹性的运输网络的越来越大的压力。然而，使用现有工具来实现这一点的一个重要障碍是，当前的评估规范规定了极限承载能力和允许承载能力之间的固定比例，考虑到现场桥梁的多样性，这是不合适的，可能导致高度不准确的桥梁评估，进而产生重大的经济影响。目前的情况源于我们对砖石拱桥的“现实世界”行为的有限理解，这种桥梁通常包含土壤填充材料，当施加荷载时，这些材料围绕拱筒并与拱筒相互作用，其中工作(循环)和最终加载制度都很重要。发展对这种行为的更好理解是这个项目的主要重点。为了实现这一目标，将进行高度仪器化的土-拱相互作用试验，使用低摩擦、透明侧面、中等和全尺寸的试验室和最先进的粒子图像测速(PIV)技术，以确保获得全面和高质量的试验数据集。测试变量将包括荷载类型(准静态与循环)、桥梁类型(道路与铁路)、填充材料类型以及近交通表面是否存在坚硬的层。将采用数值建模技术和新的“系统识别”技术，以确保在验证所开发的模型时使用通过实验获得的全部数据集。最后，最终目标是利用所获得的更好的理解来开发供工程师使用的更合理的评估工具。

There are approximately 70,000 masonry arch bridge spans on the UK road and rail networks (approx. 1 million spans worldwide), the vast majority of which are now well beyond the 120 year life usually expected of bridges. Though masonry arch bridges are in general considered long-lived structures, large numbers are now showing signs of distress. However, the cost of replacing these bridges in the UK alone would run into tens of billions of pounds, and their aesthetic and heritage value is also significant. Unfortunately the methods currently used to assess their capacity are antiquated and/or over-simplistic, making the task of prioritising renewal or refurbishment schemes extremely difficult (the still widely used MEXE method of assessment, which dates back to the 1940s, has very limited predictive capability and offers little scope for future enhancement). Weathering, continually increasing traffic volumes and factors such as the increased frequency of flood events brought about by climate change (affecting bridges over water) only serve to exacerbate the situation. Furthermore, although the primary focus of recent research has been on prediction of structural failure (the `ultimate limit state'), prediction of the level of service load above which incremental damage occurs (the `permissible limit state') is now a key priority for infrastructure owners, who are under increasing pressure to provide transport networks which are resilient. However, a significant barrier to delivering this using existing tools is that current assessment codes prescribe a fixed ratio between the ultimate and permissible load carrying capacities, which, given the diverse range of bridges in the field, is inappropriate and can lead to highly imprecise bridge assessments, and in turn to major economic implications.The present situation stems from our limited understanding of the 'real-world' behaviour of masonry arch bridges, which typically contain soil fill material surrounding and interacting with the arch barrel when loading is applied, and where both working (cyclic) and ultimate loading regimes are important. Developing an improved understanding of such behaviour is the main focus of this project. To achieve this, highly instrumented soil-arch interaction tests will be undertaken, with low-friction, clear sided, medium and full-scale test chambers and state-of-the-art Particle Image Velocimetry (PIV) techniques used to ensure a comprehensive and high quality experimental data-set is obtained. Test variables will include loading type (quasi-static vs. cyclic), bridge type (road vs. railway), fill material type and the presence or otherwise of near-traffic surface strong / stiff layers. Numerical modelling techniques and novel `system identification' techniques will be employed to ensure the full experimentally obtained data-set is used when validating the models developed. Finally, the ultimate objective is to use the improved understanding obtained to develop more rational assessment tools for use by engineers.