Duhee Park

Pore pressure model based on accumulated stress

We present a pore pressure model that predicts the build-up of residual pore pressure from accumulated shear stress. The main advantage of the model is that all of the input parameters can be selected from a CSR (cyclic stress ratio)–

Computational Coupled Method for Multiscale and Phase Analysis

N

Experimental and numerical analyses of an opening in a jointed rock mass under biaxial compression

N (number of cycles required for liquefaction) curve measured from a stress-controlled test. The formulation of the model and guidelines for selecting its parameters are presented. Comparisons with measurements validated the applicability of the model and also the parameter selection procedure. Further comparisons with another accumulated stress-based model highlight the superiority of the proposed model in terms of accuracy and ease-of-use.

Selection of the optimal frequencies of viscous damping formulation in nonlinear time-domain site response analysis

Damage analyses of rectangular cut-and-cover tunnels are performed to define the damage states and corresponding damage indices (DIs) under seismic loading. Single, double, and triple box structures designed for metro subway systems in South Korea are used. The tunnel structures are modeled by nonlinear frame elements attached to a series of normal and shear springs to simulate the soil–tunnel interaction. Pushover analyses are performed to develop the capacity curves and to monitor the development of plastic hinges. Parallel elastic analyses are also performed to determine the elastic moments at which plastic hinges form. For each tunnel and site condition, three damage states, which are minor, moderate, and extensive, are defined in terms of number of plastic hinges that form at the corners of the tunnel structure. Each damage state is linked to the corresponding DI, which is defined as the ratio of the elastic moment to the yield moment and free-field shear strain. DI for the single box tunnel is shown to be mostly independent of the shear wave velocity of soil. The values of DIs for single, double, and triple box tunnels range from 1.0 to 2.0. It is highlighted that the proposed damage state associated with DI and shear strain provide an enhanced estimate of the seismically induced damage of box tunnels and can be easily utilized in a performance-based design.

Development of probabilistic seismic site coefficients of Korea

On micro scale the constitutions of porous media are effected by other constitutions, so their behaviors are very complex and it is hard to derive theoretical formulations as well as to simulate on macro scale. For decades, in order to escape this complication, the phenomenological approaches in a field of multiscale methods have been extensively researched by many material scientists and engineers. Their theoretical approaches are based on the hierarchical multiscale methods using a priori knowledge on a smaller scale; however it has a drawback that an information loss can be occurred. Recently, according to a development of the core technologies of computer, the ways of multiscale are extended to a direct multiscale approach called the concurrent multiscale method. This approach is not necessary to deal with complex mathematical formulations, but it is noted as an important factor: development of computational coupling algorithms between constitutions in a porous medium. In this work, we attempt to develop coupling algorithms in different numerical methods finite element method (FEM), smoothed particle hydrodynamics (SPH) and discrete element method (DEM). Using this coupling algorithm, fluid flow, movement of solid particle, and contact forces between solid domains are computed via proposed discrete element which is based on SPH, FEM, and DEM. In addition, a mixed FEM on continuum level and discrete element model with SPH particles on discontinuum level is introduced, and proposed coupling algorithm is verified through numerical simulation.