Concrete gravity dams in Canada are ageing. With an average of 50 years of service, there are definite signs of deterioration, particularly along lift joints, sometimes due to inadequate construction techniques. The safety assessment of dams, including the response of lift joints under extreme loads, has not been addressed adequately in the context of advanced numerical analysis using relevant load-displacement constitutive models.; Cracking and failure along lift joints in dams involve frictional strength characteristics which, under transient loadings such as earthquakes, may lead to energy dissipation by friction sliding. Eighteen specimens with concrete-concrete joint surface area of 500mm x 250mm were subjected to sliding friction tests. The friction coefficient was found to decrease with increasing applied normal stress. Hysteresis loops are very stable; there is no significant degradation in response. The friction angle characterizing the shear strength is the sum of a basic angle and a roughness angle. Roughness of waterblasted joints is equal to 80% of monolithic cracked specimens roughness, while roughness of untreated joints is equal to 15% of monolithic cracked concrete roughness. The dynamic sliding hysteresis loops are enhanced by reducing the basic friction coefficient to 85% of the static value.; Based on the experiments, a hysteretic concrete-concrete lift joint constitutive model was developed. The initial linear elastic response of the joint interface, the crack initiation and propagation, and the fully cracked sliding friction response, were combined in a three-state constitutive model. The model was implemented into the newly developed finite element program INTRFACE that uses nonlinear gap-friction interface element as numerical support. A typical 90 m concrete gravity dam with lift joints was analysed for three possible situations: (i) a base joint at the foundation, (ii) a base joint and a lift joint near the crest, and (iii) eight lift joints evenly distributed along the dam height. Nonlinear transient dynamic analyses indicate that the total energy dissipated by friction, and the maximum residual sliding displacements could be adopted as a basis for assessing the potential damage under a severe earthquake.
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机译：加拿大的混凝土重力坝正在老化。平均服役期为50年，有时由于不完善的施工技术而有明显的恶化迹象，尤其是在提升接头处。大坝的安全性评估，包括极端载荷下的举升节响应，在使用相关的载荷-位移本构模型进行高级数值分析的背景下，尚未得到充分解决。大坝举升缝的破裂和破坏涉及摩擦强度特性，在地震等瞬态载荷下，摩擦滑动可能导致能量耗散。对18个混凝土-混凝土接缝表面积为500mm x 250mm的试样进行了滑动摩擦测试。发现摩擦系数随着施加的法向应力的增加而减小。磁滞回线非常稳定；响应没有明显降低。表征剪切强度的摩擦角是基本角和粗糙度角之和。喷水接缝的粗糙度等于整体开裂试样粗糙度的80％，而未经处理的接缝的粗糙度等于整体开裂混凝土粗糙度的15％。通过将基本摩擦系数减小至静态值的85％，可以增强动态滑动磁滞回线。在试验的基础上，建立了滞后混凝土-混凝土举升缝本构模型。接头界面的初始线性弹性响应，裂纹的萌生和扩展以及完全裂纹的滑动摩擦响应被组合在三态本构模型中。该模型已实施到新开发的有限元程序INTRFACE中，该程序使用非线性间隙摩擦界面元作为数值支持。分析了典型的90 m混凝土重力坝的三种可能情况：（i）基础的基础节，（ii）顶部附近的基础节和提升节，以及（iii）均匀分布的八个提升节沿水坝高度。非线性瞬态动力分析表明，通过摩擦耗散的总能量以及最大残余滑动位移可作为评估大地震下潜在破坏的基础。
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