Three-Dimensional Nonlinear Seismic Analysis of Gravity Dams Using a Novel Macro Shear Key Element in Contraction Joints

«ABSTRACT:Concrete gravity dams are very important structures for the production of hydroelectric energy, irrigation, water supply, and flood regulations, among other functions. However, many of today’s dams have been designed using outdated seismic codes and now require safety re-evaluations or rehabilitations. Contraction joint shear keys have been included in several of these dams and may provide additional shear resistance that may not have been considered in the design. Typically, the capacity of shear keys is evaluated as the sum of friction and cohesion that can be mobilized across a plane located at the base of the keys. Numerically, keyed contraction joints are usually modelled using Mohr-Coulomb failure criteria. However, not much consideration is given to the nonlinear softening of the shear keys, the effect of multi-axial loading on shear keys, the possibility of initial joint opening, the size effect of having multiple keys along the joint, or the effect of water penetration in the contraction joints during seismic excitation. In this dissertation, the shortcomings of the traditional methods for considering shear keys in gravity dam contraction joints are addressed by first performing nonlinear finite element parametric analyses on detailed numerical models of shear keys. Failure envelopes for the interaction between confinement pressure, shear and bending moment and for the interaction between confinement pressure, shear and torsion at the shear key scale are obtained. Then, a new Macro Shear Key Joint Element (MSKJE) is developed as a user define element in the computer program LS-Dyna and calibrated using the data obtained from the parametric analyses. The MSKJE accurately reproduces the monotonic and cyclic loading-displacement responses of the detailed shear key numerical models while significantly reducing the computational cost. This allows modelling the shear keys in the contraction joints of a complete dam finite element model without running into problems with stress concentration at the corners of the shear keys or extremely high computational time due to very fine meshes.»