Understanding the cracking behaviour of reinforced concrete elements subjected to the restraint of imposed strains

该项目的总体目标是为执业工程师提供正确设计RC构件的能力，以约束短期和长期施加的应变。有边或边端约束组合的墙体的裂缝宽度和间距取决于纵横比和高度，这在目前的设计中没有考虑。此外，在实践中还会出现不同理想约束类型的组合。该研究项目将量化这些影响。研究了影响渗漏和钢筋耐久性的内裂纹分布。通过本文提出的试验测试和NLFEA，该项目将能够为工程师提供控制挡土墙、桥台、水库墙、大型地下室、隧道和楼板等RC结构的约束裂缝宽度的改进设计方法。这种更精确的设计能力增强的结果将是更好地估计服务性能，这将减少不合规事件，从而减少维修成本/时间延迟/诉讼。实验结果将与数值研究进行比较，以便充分发展一种理论，能够在所有约束条件下设计裂缝控制的钢筋。所寻求的主要目标是：1。通过一项实验研究来发展对行为的物理理解，该实验研究将检查施加变形对裂缝宽度的影响，墙体几何形状，约束类型以及加强的数量和安排。2. 2 .开发具有边缘和末端约束组合的壁面裂缝宽度的NLFEA模型（BS8007中的图A3和BS EN1992-3中的图L.1）开发一种面向设计的分析程序，用于受施加应变约束的墙体裂缝控制钢筋的设计。该程序将由实验室检查和NLFEA通知。它将对各种可能形式的限制和强加的压力进行连贯的处理。4. 通过与墙体的现场数据进行比较，进一步验证所产生的程序，其中有足够的信息可以建立自由应变和约束，约束引起的RC裂缝目前是英国建筑行业在生产力损失和维修成本方面的重大成本。目前的规范不足以解决这个问题，需要进一步的指导。最近，在建筑业挑战2025中，有很大的动力为这些任务做出贡献。“建筑2025”的具体目标是将总成本降低33%，这可以通过提高设计效率来实现，这也是本研究的预期结果。这项工作与EPSRC的“工程”主题紧密相关，对RC元件的可用性极限状态性能有了更好的理解，进一步连接了“能源”和“全球不确定性”。产出将适用于许多UKRI研究领域（建筑环境，海岸和水道工程，地面工程，工程设计，结构工程和水工程）；数值和分析研究也使其完全符合投资于结构无损评价研究领域（机械结构性能）的策略和1.38亿英镑的UKCRIC资本投资。该项目是利兹大学和伦敦帝国理工学院资助的EPSRC合作项目的一部分。两所大学的合作促进了两地的学习、知识转移和思想交流；汇集资源也将确保在整个学术界更好地传播。直接参与的内维尔水泥和混凝土工程卓越中心（NC）将通过其学术指导委员会成员，为相关合作提供传播手段和论坛。

The overall aim of the project is to provide practising engineers with the ability to correctly design RC elements for the restraint of short and long-term imposed strains. Crack width and spacing in walls with edge or combined edge and end restraint depend on aspect ratio and height which is not accounted for in current design. Furthermore, a combination of different idealised restraint types occurs in practice. The research project will quantify these influences. The internal crack profile, which affects leakage and reinforcement durability will also be studied. Through the experimental testing and NLFEA proposed here the project will be able to provide engineers with improved design methods for controlling restraint induced crack widths in RC structures such as retaining walls, bridge abutments, reservoir walls, large basements, tunnels and slabs. The result of this enhanced ability to design more accurately will be better estimation of serviceability performance, which will reduce episodes of non-compliance and hence repair costs / time delays / litigation. The experimental output will be compared with numerical studies in order to sufficiently develop a theory enabling the design of reinforcement for crack control under all restraint conditions. The main objectives sought are: 1. To develop physical understanding of behaviour through an experimental study which will examine the influences on crack width of imposed deformation, wall geometry, restraint type and the amount and arrangement of reinforcement. 2. To develop NLFEA models which enable the realistic calculation of crack width in walls with combinations of edge and end restraints (Figure A3 in BS8007 and Figure L.1 in BS EN1992-3) 3. To develop a design oriented analytical procedure for the design of crack control reinforcement in walls subject to restraint of imposed strain. The procedure will be informed by the laboratory tests and NLFEA. It will give a coherent treatment of the various possible forms of restraint and imposed strains. 4. Further validation of the resulting procedures by comparison with field data from walls, where sufficient information exists to enable the free strains and restraint to be established Restraint induced cracking in RC is currently a significant cost to the UK construction industry both in terms of lost productivity and repair cost. Current codes are inadequate to design out this problem and further guidance is needed. Lately, there is great drive to contribute to such tasks as seen in the Construction Industry Challenge 2025. Construction 2025 has a specific target of a 33% reduction in overall costs - this can be achieved through efficiency in design which is also an expected outcome of this research. The work sits solidly within the EPSRC theme of 'Engineering', with the improved understanding of the serviceability limit state performance of RC elements bridging further to 'Energy' and 'Global Uncertainties'. The output will be appropriate to many of the UKRI Research Areas (Built Environment, Coastal and Waterway Engineering, Ground Engineering, Engineering Design, Structural Engineering and Water Engineering); the numerical and analytical studies also make it fit perfectly with the strategy of investment into the research area of non-destructive evaluation of structures (Performance of Mechanical Structures) and the £138M UKCRIC capital investment. The project is part of a much larger funded EPSRC collaborative project between the University of Leeds and Imperial College London. The collaboration between the two universities facilitates better learning, knowledge transfer and exchange of ideas; pooling of resources will also ensure better dissemination across the academic community. The directly involved Neville Centre (NC) of Excellence in Cement and Concrete Engineering at UoL through its academic Steering Committee members, will provide dissemination means and forum for relevant collaborations.