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

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.