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

有大量的商业压力推动钢筋混凝土多层结构朝着更长跨度和更薄的结构深度发展。明确的开放空间的潜在好处，放置服务的自由和建筑物高度的降低（以及随后可能降低的覆层成本），或者相反，在建筑物中加入额外楼层的能力（从而增加租金潜力）可以对方案的整体经济性产生重大影响。然而，这些好处不能被充分利用，直到它是可能的准确预测混凝土元件的长期挠度。在预测开裂混凝土受弯构件的长期挠度的一个主要问题一直是难以隔离的变形由于收缩从其他参数的影响，如徐变和拉伸硬化。目前的规范预测长期变形的裂缝混凝土元件使用的方法开发的无裂缝的部分，但纳入开裂部分的属性。虽然对于无裂纹截面，这一点的正确性是毫无疑问的，但对于有裂纹截面，这一点从未得到实验验证。因此，它可能是非常保守的，因此，对设计策略有限制性的影响。收缩对开裂截面的影响仍不确定，因为无法通过实验确认其影响。本申请人现在相信有可能克服这一困难，并且本申请提出了一种非常创新的实验方法，该方法将允许收缩对开裂构件的变形的影响首次被隔离。最近，申请人在EPSRC资助的项目下进行的研究使人们更好地理解了张力硬化现象，特别是其随时间的衰减。蠕变的影响已经普遍得到了很好的理解。拟议研究的结果，以及利兹和达勒姆混凝土研究小组获得的关于张力硬化的数据，最终将使设计人员能够以更高的可靠性预测开裂混凝土受弯构件的长期挠度。当前建筑行业的气候及其对钢材成本和可用性的影响是领先的，并将继续领先。在建筑中增加使用混凝土（例如，利兹的主要新克拉伦斯码头开发项目，以前会选择钢材）。因此，这项研究非常及时。现在更重要的是，这些信息是提供给设计师，以确保在设计和使用混凝土的最大效率是实现，以便不限制他们在英国和欧盟建筑行业的竞争力。拟议的研究将在利兹大学和达勒姆大学进行。实验方案包括两个阶段。第一阶段是确认方法。第二阶段将使用研究人员提出的创新方法隔离收缩的影响，有助于改进设计方法和更准确地评估收缩。该提案有6个工业合作者提供实物和现金捐助，共计33 460美元。这两所大学申请的资金总额为274，537美元。

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.