Shrinkage Curvature of Cracked Reinforced Concrete Sections: Improving the Economy of Concrete Structures Through Good Science

There are substantial commercial pressures driving the current trend in reinforced concrete multi-storey structures towards longer spans and thinner structural depths. The potential benefits of clear open spaces, the freedom of placing services and the reduction of building height (and the subsequent potential reduction in cladding costs) or conversely, the ability to incorporate an extra floor in the building (thus increasing rental potential) can have a significant effect on the overall economics of a scheme. However, these benefits cannot be fully exploited until it is possible to predict accurately the long-term deflection of concrete elements.A major problem in predicting the long-term deflection of cracked concrete flexural elements has always been the difficulty in isolating the deformation due to shrinkage from the effect of other parameters such as creep and tension stiffening. Current codes predict the long-term deflection of cracked concrete elements by using the approach developed for uncracked sections but incorporating cracked section properties. Whilst there is no question of the correctness of this in relation to uncracked sections, it has never been experimentally validated for cracked sections. Consequently, it may be extremely conservative and, therefore, have a restrictive influence on design strategy. The effect of shrinkage on a cracked section remains uncertain as it has not been possible to confirm the influence experimentally. The applicants now believe it is possible to overcome this difficulty and this application proposes an extremely innovative experimental approach which will allow the effect of shrinkage on the deformation of cracked members to be isolated for the first time. Recently, research by the applicants under a previous EPSRC funded project has resulted in a much better understanding of the tension stiffening phenomenon and, in particular, its decay with time. The effects of creep are already generally well understood. The results of the proposed research, and the data obtained by the Leeds and Durham concrete research team on tension stiffening, will finally allow designers to predict the long-term deflection of cracked concrete flexural elements with greater reliability.The current climate within the construction industry and the effect this has had on the cost and availability of steel is leading, and will continue to lead, to an increased use of concrete in construction (e.g. the major new Clarence Docks development in Leeds, where previously steel would have been chosen). The research is, therefore, very timely. It is now even more critical that this information is available to designers to ensure that maximum efficiency in the design and use of concrete is achieved so as not to restrict their competitiveness within the UK and EU construction industry.The proposed research will be performed at both the University of Leeds and the University of Durham. The experimental programme consists of two stages. The initial stage is concerned with confirmation of methodology. The second stage will isolate the effect of shrinkage using the innovative approach proposed by the investigators, contributing to an improved design method and more accurate assessment of shrinkage. The proposal has 6 industrial collaborators providing in-kind and cash contributions totalling 33,460. The total amount of funding being sought by the two universities is 274,537.