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资深工程师提供正确设计RC构件的能力，以限制短期和长期施加的应变。有边约束或边端约束组合墙体的裂缝宽度和间距取决于高宽比和高度，这在目前的设计中没有考虑到。此外，在实践中还出现了不同理想化约束类型的组合。该研究项目将量化这些影响。还将研究影响渗漏和钢筋耐久性的内部裂缝分布。通过试验测试和提出的非线性有限元分析，该项目将能够为工程师提供改进的设计方法，以控制挡土墙、桥台、水库墙、大型地下室、隧道和楼板等钢筋混凝土结构的约束裂缝宽度。这种更准确设计的增强能力的结果将是对适用性性能的更好估计，这将减少不遵守规定的事件，从而减少维修费用/时间延误/诉讼。实验结果将与数值研究结果进行比较，以便充分发展一种理论，使钢筋在所有约束条件下都能进行裂缝控制设计。所寻求的主要目标是：1.通过实验研究来发展对行为的物理理解，该实验研究将考察施加变形、墙体几何形状、约束类型以及配筋的数量和布置对裂缝宽度的影响。2.开发NLFEA模型，使具有边缘和端部约束组合的墙中的裂缝宽度能够实际计算(BS8007中的图A3和BS EN1992-3中的图L.1)3.为受外加应变约束的墙中的裂缝控制钢筋的设计开发面向设计的分析程序。该程序将由实验室测试和NLFEA告知。它将对各种可能的约束形式和施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，进一步验证了所产生的程序，在墙体的现场数据中，有足够的信息能够建立自由应变和约束。在RC中，约束引起的裂缝目前是英国建筑业在生产力损失和维修费用方面的一项重大成本。目前的法规不足以解决这个问题，需要进一步的指导。最近，人们有很大的动力为这些任务做出贡献，就像在2025年建筑业挑战中看到的那样。《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。这项工作牢牢地围绕着EPSRC的“工程”主题展开，随着对RC构件适用性极限状态性能的更好理解进一步与“能源”和“全球不确定性”联系在一起。其结果将适用于英国建筑工程研究院的许多研究领域(建筑环境、海岸和航道工程、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与结构无损评估(机械结构性能)研究领域的投资战略和1.38亿GB的UKCRIC资本投资完美契合。该项目是利兹大学和伦敦帝国理工学院之间一个规模更大的EPSRC合作项目的一部分。两所大学之间的合作促进了更好的学习、知识转移和思想交流；汇集资源也将确保在学术界更好地传播。通过其学术指导委员会成员直接参与的内维尔大学水泥和混凝土工程卓越中心(NC)将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.