Effect of cycling temperature on propagation of tensile fatigue cracks in concrete mass dams

对马尼托巴的整体混凝土坝进行的稳定性审查发现，如果裂缝是由循环热应力引发的，那么随后通过裂缝增加的内部水压将导致裂缝扩展，从而增加结构不稳定的风险。马尼托巴水电公司启动了一个项目，审查、研究和测试，以确保混凝土的抗拉强度，特别是在施工缝处，可以继续依赖，以提供防止滑动破坏的安全所需的凝聚力。需要对混凝土进行研究和测试，以评估由于热循环而导致的强度劣化。 作为稳定性审查的一部分进行的有限元分析（FEA）表明，大体积混凝土结构的季节性升温和降温产生了每年一次的差异运动周期，导致大坝上游面的应力在拉伸和压缩之间转换。由这些温度循环引发的裂缝扩展以及随后的大体积混凝土拉伸疲劳对大坝稳定性的风险还没有得到很好的理解。该项目将有助于估计热循环下的裂纹扩展速率。本研究的目的是调查温度波动和由此产生的循环拉压应力对混凝土的长期耐久性的影响，以及施工缝的耐久性的影响。本研究将培养9名HQP，硕士和学士各3名，博士1名。学生和两名博士后研究员。这项研究将使马尼托巴水电和其他大坝业主评估这些结构的安全性，防止可能的不稳定，由于开裂。这些结果将通过更好地了解对稳定性的威胁以及必要时对监测和监督的修改，为正在进行的马尼托巴水电大坝安全计划提供信息。

A stability review of monolithic concrete dams in Manitoba discovered that if a crack was initiated by cyclic thermal stress, the subsequent increase in internal water pressure via the crack would cause the crack to propagate leading to increased risk of instability of the structure. Manitoba Hydro initiated a project to review, research and test to ensure the tensile strength of the concrete, particularly at construction joints, can continue to be relied on to provide the cohesion necessary for safety against sliding failure. Research and testing of concrete is required to evaluate strength deterioration due to thermal cycling. The finite element analysis (FEA) performed as part of the stability review shows that the seasonal warming and cooling of the mass concrete structure generates an annual cycle of differential movement causing the stress in the upstream face of the dam to shift between tension and compression. The risk to the dam stability from crack propagation initiated by these temperature cycles and subsequent tensile fatigue in mass concrete are not well understood. This project will help to estimate the rate of crack growth under thermal cycling. The objective of this study is to investigate the impact of the temperature fluctuations and resulting cyclic tensile and compressive stresses on the long-term durability of concrete, and the impact on the durability of the construction joints. This study will train nine HQP, three each at the Master's and Bachelor's level, one Ph.D. student and two post-doctoral fellows. This research will enable Manitoba Hydro and other dam owners to assess the safety of these structures against possible instability due to cracking. The results will inform the ongoing Manitoba Hydro dam safety program through better understanding of threats to stability as well as modifications to monitoring and surveillance, if required.