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元件的能力，以抑制短期和长期施加的应变。在有边缘或边缘和端部联合约束的墙体中，裂缝宽度和间距取决于纵横比和高度，而这在当前设计中没有考虑。此外，在实践中会出现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轮廓。通过实验测试和NLFEA这里提出的项目将能够为工程师提供改进的设计方法，用于控制约束引起的裂缝宽度的钢筋混凝土结构，如挡土墙，桥台，水库墙，大型地下室，隧道和板。这种增强的更准确设计能力的结果将是更好地估计适用性性能，这将减少不合规事件，从而减少维修成本/时间延迟/诉讼。将实验输出与数值研究进行比较，以充分发展一种理论，使所有约束条件下的裂缝控制钢筋的设计。主要目标是：1.通过实验研究，研究施加变形、墙体几何形状、约束类型以及钢筋数量和布置对裂缝宽度的影响，从而对行为形成物理理解。2.开发NLFEA模型，使裂缝宽度的实际计算与边缘和端部约束的组合（图A3在BS 8007和图L.1在BS EN 1992 -3）3。发展一种面向设计的分析程序，用于受外加应变约束的墙体中裂缝控制钢筋的设计。该程序将通过实验室测试和NLFEA进行通知。它将对各种可能的限制和强加的压力形式给予连贯的处理。4.通过与来自墙壁的现场数据进行比较，进一步验证所产生的程序，其中存在足够的信息以使自由应变和约束能够被建立。约束引起的RC开裂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。目前的规范不足以设计出这个问题，需要进一步的指导。最近，人们有很大的动力为2025年建筑业挑战赛中看到的这些任务做出贡献。建设2025有一个具体的目标，即降低33%的总成本-这可以通过设计效率来实现，这也是本研究的预期成果。这项工作牢固地坐落在EPSRC的主题“工程”，与钢筋混凝土元件的正常使用极限状态性能的进一步桥接到“能源”和“全球不确定性”的理解。输出将适合许多UKRI研究领域（建筑环境，海岸和航道工程，地基工程，工程设计，结构工程和水利工程）;数值和分析研究也使其完全符合投资战略的非破坏性评估结构的研究领域（机械结构的性能）和£ 1.38亿UKCRIC资本投资。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资助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。直接参与的内维尔中心（NC）卓越的水泥和混凝土工程在UoL通过其学术指导委员会成员，将提供相关合作的传播手段和论坛。

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.