Resilient rail infrastructure: dissipation driven fracture analysis of concrete support systems

英国的铁路基础设施目前每年支持13亿人次的客运和1亿吨的货运。仅货运业就为英国经济贡献了8.7亿英镑。过去10年，该部门的客运量和货运量分别增长了40%和60%，预计未来30年，客运量将翻一番，货运量将增长140%。随着网络的发展，即使在过去的10年里，应用于铁路支撑系统的载荷的大小和频率也显著增加。据估计，在2009至2014年间，英国铁路运营商Network Rail(NR)将投资37.5亿GB在轨道上维护该网络。这条3.2万公里的铁路基础设施中的绝大多数由预应力混凝土轨枕(PCS)和交叉支架(CBS)支撑。这些混凝土构件为运行中的钢轨提供横向约束和垂直支撑。PCSS和CBS依次在三面由轨道道碴支撑；碎石直径30-50 mm。自1950年代引入以来，PCS已经在新轨道上取代了传统的木枕，而NR每年用PCS取代大约20万个木材枕木。然而，尽管英国的铁路网依赖于这些混凝土结构，而且它们的几何形状很简单，但令人惊讶的是，人们对它们的结构行为知之甚少。NR的CP5交付计划估计，2013/14年期间支撑网络的轨枕的使用寿命为60.9%，同一时间段内将发生5,918条轨道故障。有人担心，混凝土支撑构件中裂缝的发展正在破坏铁路网。为了维护一个安全、可靠和有弹性的铁路网，必须了解如何设计混凝土支撑系统以抵御日益增长的结构需求。拟议的研究涉及三维动态分析，以评估PCSS和CBS的结构稳健性，使用一种新的计算力学框架和相关的数值分析技术。如果成功，这项研究将为各种工程材料的断裂建模提供一个变革性的、完整的和一致的框架。这一提议的创造性在于，将本构模型、断裂力学和数值分析技术中的最新想法应用于英国铁路基础设施中一个知之甚少但却至关重要的组成部分。它将提供一个框架，在此框架内开发新的弹性钢轨支撑系统紧固方法。

The UK's rail infrastructure currently supports 1.3 billion passenger journeys and 100 million tonnes of freight each year. The freight transport alone contributes £870 million to the UK economy. The sector has seen 40% and 60% increases in passengers and freight over the last 10 years, respectively, and it is expected that passenger numbers will double and freight increase by 140% over the next 30 years. As the network has developed the magnitude and frequency of loads applied to the rail support systems have increased significantly, even over the last 10 years. It is estimated that between 2009 and 2014, the UK's rail operator, Network Rail (NR), will invest £3.75bn in track to maintain the network. The vast majority of this 32,000km of rail infrastructure is supported by pre-stressed concrete sleepers (PCSs) and crossing bearers (CBs). These concrete members provide lateral restraint and vertical support to the running steel rails. The PCSs and CBs are in turn supported on three sides by track ballast; crushed stone 30-50mm in diameter. Since their introduction in the 1950s, PCSs have superseded traditional wooden sleepers in new track and NR replaces approximately 200,000 timber sleepers each year with PCSs. However, despite the reliance of the UK's rail network on these concrete structures, and the simplicity of their geometry, surprisingly their structural behaviour is poorly understood. NR's CP5 delivery plan estimated that the used life of the sleepers supporting the network for the 2013/14 period is 60.9% and that 5,918 track failures would occur during the same timeframe. There are concerns that the development of fractures in concrete supporting members is undermining the rail network. In order to maintain a safe, reliable and resilient rail network it is essential to understand how the concrete support systems can be designed to future proof them against ever increasing structural demands.The proposed research is concerned with three-dimensional dynamic analysis to assess the structural robustness of PCSs and CBs using a novel computational mechanics framework and associated numerical analysis technique. If successful, this research will provide a transformative, complete and consistent framework for modelling fracture in a variety of engineering materials. The creativity of this proposal lies in the application of up-to-the-minute ideas in constitutive modelling, fracture mechanics and numerical analysis techniques to a poorly understood yet critical component of the UK's rail infrastructure. It will provide a framework within which to develop new resilient rail-support system fastening methods.