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

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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.**