Structural Safety Assessment and Strengthening of Concrete Dams and Gated Spillways Subjected to Severe Loading Conditions

拟议研究计划的长期目标是开发有效的结构评估和混凝土水工结构的修复策略，从而大大节省昂贵的补救工作。拟议的研究方案提出了两个相辅相成的项目。项目1：混凝土坝的地震安全性：多轴荷载下的三维剪切键有限元模型及试验验证：已有的几个重力坝已在坝体之间建立了收缩缝剪键。在最初的二维设计中，这些键被认为不能提供坝块之间的荷载传递。然而，剪切键在整体之间提供了一些联锁机制。因此，剪切键是具有弹性的特征，可以考虑将地震残余滑动位移降至最低，从而影响地震后顶块闸门的运行。到目前为止，剪切键通常用非常简单的接触单元来建模，忽略了(I)轴向剪力矩-扭矩之间的三维载荷传递相互作用导致应力集中和潜在的过早破坏，(Ii)由于热效应而初始开口的影响，(Iii)较硬或较弱键失效时的脆性破坏的可能性。该项目的目标是对一种考虑多轴破坏包络的新型薄节点“剪切键”有限元单元进行实验验证。实验测试程序将在带有剪切键的混凝土小砌块上进行，使用一台新型的大容量六自由度试验机。将进行全面的有限元分析，以评估建模参数对控制残余地震滑动位移的影响，包括使用被动锚杆或主动锚杆进行加固。项目2-混凝土大坝安全评估和加固：被动锚杆的可靠使用：现有破裂的混凝土部件通常使用被动钢锚杆进行稳定。然而，考虑三维载荷的强度评估需要改进，以实现可靠性和最优化。此外，旧混凝土溢洪道桥墩的设计几乎完全是为了抵御静水推力，它包含的升降接头被少量的钢筋拦截，而不是限制在周边。由于相关破坏机制的不确定性，这些杆件在稳定性评估中被忽略。该项目的目标是开发和实验验证先进的有限元和简化方法(I)可靠地使用3D被动钢锚杆加固方案，以及(Ii)考虑到码头现有的少量加固。通过实验获得了主要拉伸和双向剪切载荷下的三维破坏包络。利用试验结果和有限元模拟，将进行考虑现有桥墩的案例研究。将为实际工程应用制定设计准则和简化分析方法。

The long term objectives of the proposed research program are to develop effective structural assessment and rehabilitation strategies of concrete hydraulic structures that will permit substantial saving of costly remedial work. The proposed research program presents two complementary projects. Project 1: Seismic Safety of Concrete Dams: 3D Shear Key Finite Element Model and Experimental Validation for Multi-Axial Loadings: Several existing gravity dams have been constructed with contraction joint shear keys between monoliths. In the initial 2D design, these keys are not considered able to provide load transfer between dam blocks. However, shear keys are providing some interlocking mechanisms between monoliths. Shear keys are thus resilient features that could be considered to minimise seismic residual sliding displacements compromising post-earthquake crest block gate operation. So far, shear keys have been most often modelled with very simplified contact elements ignoring (i) 3D load transfer interactions between axial-shear-moment-torsion leading to stress concentrations and potentially premature failure, (ii) effects of initial openings due to thermal effects, (iii) the potential for brittle failure upon failure of a stiffer or weaker key. The project objectives are to conduct experimental validation of a novel thin joint "shear key" FE element considering multi-axial failure envelopes. The experimental testing program will be performed on small concrete blocks with shear keys using a novel high capacity 6 degrees-of-freedom testing machine. Comprehensive FE analyses will be performed to assess the effects of modeling parameters to control with confidence residual seismic sliding displacements, including strengthening actions using passive or active anchors. PROJECT 2- Concrete Dam Safety Assessment and Strengthening: Reliable Use of Passive Anchors: Existing cracked concrete components are often stabilised using passive steel anchors. However, strength assessment considering 3D loadings needs to be improved for reliability and optimisation. Moreover, old concrete spillway piers, designed almost exclusively to resist hydrostatic thrusts, contain lift joints that are intercepted by a small amount of reinforcing bars, not confined along the perimeter. These bars are ignored in stability assessment because of uncertainties regarding related failure mechanisms. This project objectives are to develop, and experimentally validate, advanced FE and simplified methodologies (i) for a reliable use of 3D passive steel anchors strengthening schemes, and (ii) to take into account the small amount of existing reinforcement in piers. 3D failure envelopes under dominant tensile and biaxial shear loads will be experimentally obtained. Using the experimental findings and FE simulations, case studies considering existing piers will be conducted. Design guidelines and simplified analysis method for practical engineering applications will be developed.