Large-scale Numerical Simulation For Damage Prediction Of High Arch Dams Subjected To Earthquake Shocks

As an important part of the Western Development Strategy, West-East Power Transmission program promoted the construction of quite a few high dams, in which concrete arch dams have been widely employed. As we all know, the aseismic safety is crucial to high arch dams in southwest China. With the support from National Nature Science Foundation of China under Grants 50139010 and 90510018, in-depth research was conducted regarding the large-scale numerical simulation of high arch dams in strong earthquakes.1. High arch dams may get fractured or damaged in strong earthquakes, which should be considered in its aseismic safety evaluation. As is known that concrete is inhomogeneous on the mesoscopic level, and taking advantage of this fact could better simulate the fracture process of concrete structures. However, as far as high concrete dams are concerned, it would be impossible and unnecessary to precisely simulate this inhomogeneity. If the arch dam is modeled with meshes fine enough, every mesh can be regarded as homogeneous, while the mesoscopic inhomogeneity is taken into account via random distribution of material properties of the element. In the meantime, the plasticity and anisotropism of every single element can be neglected. In the presented model for damage analysis of arch dams, elastic damage constitutive equations together with simple failure criterions, i.e., Mohr-Coulomb Principle with tension cut-off, are employed to simulate the nonlinearity of concrete. Taking the Dagangshan Arch Dam as an example, numerical result accords with results of shaking table test, which verifies the validity of the presented model. An important feature of this model is simplicity, which avails its application to large-scale computation. Last but not least important, the conversion from continuity to discontinuity can be simulated with this single model. On this basis, certain factors that affect the damage status of arch dams such as joints and radiation damping of the unbounded media are further investigated.2. Much research work has been conducted in the field of structure-foundation interaction, but these work seldom focused on the large scale analysis of massive structures such as high arch dams. The Damping Solvent Extraction Method (DSEM) as proposed by Wolf and Song simulate radiation damping in a novel way. Artificial damping is introduced into the near field adjacent to the structure, and is extracted afterwards. Then the stiffness matrix of the unbounded media can be obtained by applying an assumption. DSEM avoided the convolution integral generally obssessing other methods and possesses the potential for application to large scale computation. However, DSEM is now only employed in 2D SSI problems, and pitifully with low computation efficiency and small capacity. By extending this model into 3D problems, together with in-depth research on the algorithm and matrix storage styles, a DSEM-based interaction model in the time domain for large scale computation of high arch dams is presented. Based on parametric study, relevant parameters are suggested:dl/b=1～1.5 and l=2～3b . Here d refers to the undimensional artificial damping, 1 is the size of the near field while b is the characteristic length of the foundation. The presented model is employed in the damage simulation of Dagangshan Arch Dam subjected to strong earthquakes. And it's observed that the damage of arch dam is greatly alleviated with the radiation damping considered.3. With limited computational capacity for large scale finite element analysis, meshes of different sizes may be employed according to the significance of different parts of the system considered. Then techniques for transition between coarse and fine elements should be introduced. Three methods for transition are proposed, viz. the Springed Joint Method, the Master DOF (Degree of Freedom) Method and the 13-node element. The former is based on Qiang Tianchi's interface coupled method which was founded according to the least potential energy method. As in the Joint Element Method, with fictitious nodes and sub elements technique employed, the integral in Qiang Tianchi's version is simplified and transition between two sets of coordination which requires high precision is avoided. The Master DOF Method utilizes displacement constraint and needs only simple matrix operation in application. While in the 13-node element, the integration region is divided into four sub-regions, each with linear interpolating functions. All the three methods guarantee the displacement coordination between coarse elements and fine elements. Their accuracy and feasibility were verified, and the 13-node element has been employed in the damage simulation of high arch dams subjected to strong earthquakes.4. The aseismic evaluation of high arch dams calls for large-scale and efficient numerical simulation. Personal computer, despite its rapid development, can hardly meet the needs. High performance parallel computing is the ultimate solution to this problem. A PC cluster was setup with 4 personal computers and high-speed network to be the parallel computation platform. And a parallel program PDPAD was developed for numerical simulation of damage process of high arch dams in strong earthquakes. Based on Domain Decomposition Method, the proposed damage simulation model as detailed in Chapter 2 is programmed to parallel finite element codes with MPI (Message Passing Interface) in FORTRAN 9.0 on Linux Redhat 9.0. PDPAD exhibits high scalability and speedup ratio and has the ability for large scale computation. It is employed in the damage process simulation of Dagangshan Arch Dam and can handle more than one million DOFs on the 4-node platform.