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

英国公路和铁路网络上约有70，000座石砌拱桥（约100，000座）。世界上有100万座桥梁），其中绝大多数已经远远超过了通常预期的120年寿命。虽然圬工拱桥一般被认为是长寿的结构，但大量的圬工拱桥现在已经显示出损坏的迹象。然而，仅在英国更换这些桥梁的成本就将达到数百亿英镑，其美学和遗产价值也很重要。不幸的是，目前用于评估其容量的方法过时和/或过于简单，使得更新或翻新计划的优先级排序任务极其困难（仍然广泛使用的MEXE评估方法，可追溯到20世纪40年代，预测能力非常有限，未来改进的余地很小）。气候变化、交通量持续增加以及气候变化造成的洪水事件频率增加（影响水上桥梁）等因素只会加剧这种情况。此外，虽然最近研究的主要重点是预测结构破坏（“极限状态”），但预测服务负荷水平（“允许极限状态”）现已成为基础设施所有者的一个关键优先事项，因为他们面临着越来越大的压力，必须提供具有复原力的运输网络。然而，使用现有工具实现这一目标的一个重大障碍是，当前的评估规范规定了极限承载力和允许承载力之间的固定比率，鉴于该领域的桥梁范围不同，这是不合适的，可能导致高度不精确的桥梁评估，而这反过来又会对经济产生重大影响。目前的情况源于我们对圬工拱桥的“现实世界”行为的有限理解，其通常包含土填充材料，所述土填充材料围绕拱筒并在施加载荷时与拱筒相互作用，并且其中工作（循环）和极限载荷状态都很重要。提高对此类行为的了解是该项目的主要重点。为了实现这一目标，将进行高度仪器化的土拱相互作用测试，使用低摩擦，透明侧，中等和全尺寸的测试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实验数据集。试验变量将包括荷载类型（准静态与循环荷载）、桥梁类型（公路与铁路）、填充材料类型以及是否存在近交通面强/硬层。将采用数字建模技术和新的“系统识别”技术，以确保在验证所开发的模型时使用全部实验获得的数据集。最后，最终的目标是利用改进的理解，开发更合理的评估工具，供工程师使用。

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.