Dimitris L. Karabalis

Dynamic response of 3-D flexible foundations by time domain BEM and FEM

Abstract The response of three-dimensional linear elastic foundations of arbitrary shape placed on a homogeneous, isotropic and linear elastic soil medium to dynamic disturbances is numerically obtained. Both external forces and obliquely incident seismic waves of arbitrary time variation are considered. The numerical method employed is a combination of the time domain Boundary Element Method used for the soil medium and the Finite Element Method used for the flexural foundation plate. This method has advantages over frequency domain techniques in that it provides in a natural and direct way the time history of the response and forms the basis for extension to non-linear problems.

Dynamic response of 3-D embedded foundations by the boundary element method

Abstract The dynamic response of three-dimensional rigid embedded foundations of arbitrary shape, resting on a linear elastic, homogeneous, and isotropic half-space is numerically obtained. The foundations are subjected either to externally applied forces or to obliquely incident seismic body or surface waves of arbitrary time variation. The time domain boundary element method (BEM) is utilized to simulate the soil medium with the aid of Stokes fundamental solutions. The dynamic response of the foundation-soil system is obtained in a step-by-step time-marching solution. Use of this time domain BEM requires a minimum amount of surface discretization only and provides the basis for an extension to nonlinear soil-structure interaction (SSI) problems.

Simulation of earthquake ground motions by a deterministic approach

Abstract A numerical method is presented for the computation of artificial earthquake records consistent with any arbitrarily specified target response spectra or power spectral density requirements. The proposed algorithm does not create new time histories but rather modifies, on the basis of an iterative deterministic approach, existing records to fit specific design requirements. The efficiency of the algorithm and the accuracy of the fitting process are substantially improved on the basis of a predictor–corrector type approach. The associated integrated computer code can, among its many other features, produce artificial earthquake records consistent with a number of compatible target response spectra at various damping levels, perform quadratic baseline correction, and calculate correlation factors for up to three earthquake records.

A simplified 3-D time domain BEM for dynamic soil-structure interaction problems

Abstract The numerical treatment of the fundamental singular solutions of the Stokes state of quiescent past and their implementation within the framework of a 3-D time domain BEM formulation for linear elastodynamics is discussed. Of particular interest are simplified time and space integrations of the above fundamental solutions. The accuracy as well as the efficiency of such simplified computations are tested through comparison studies against other more computationally intense BEM techniques on the basis of some benchmark SSI problems.

Inertial soil-foundation interaction by a direct time domain BEM

A direct time domain BEM formulation of the general inertial SSI problem is presented. The dynamic response of a rigid massive foundation resting on the surface of a linear elastic, homogeneous, isotropic half-space and subjected to externally applied forces is computed for illustration purposes. Results for rectangular and circular foundations are presented assuming, i) complete bond with the half-space, and ii) relaxed boundary conditions. Comparison studies with frequency domain or simplified time domain analyses confirm the results of this study.

Formulation of 3-D dynamic SSI analysis involving contact nonlinearities by time domain BEM-FEM

Abstract The formulation of a hybrid time domain BEM-FEM scheme is developed for the solution of three-dimensional dynamic soil-structure interaction problems involving contact nonlinearities at the soil-structure interface. Both uplift and sliding are considered at the interface through special thin-layer interface elements. The linear elastic structure, the geometrically nonlinear interface and the linear elastic soil medium are coupled together through equilibrium and compatibility and the analysis proceeds stepwise in time with iterations at each time step in order to define the contact area. Both external dynamic loads and seismic waves are considered.

Transient solution of 2-D flow in unconfined coastal aquifers

Abstract A BEM formulation is proposed for the 2-D groundwater flow in coastal unconfined aquifers. A quasi-steady approximation technique is utilized which allows for a BEM discretization of only the boundary of the physical domain occupied by fresh water. The objective of the proposed solution is the location of the two moving boundaries of the fresh water domain, i.e. the water table and the saltwater/fresh water interface, under conditions of transient tidal fluctuation, rainfall, and/or pumping. A comparison study and solutions to transient example problems are presented.

Efficient Time and Space Integrations of Stokes Fundamental Solutions — Applications to a Direct Time Domain BEM for Elastodynamics

The numerical treatment of the fundamental singular solutions of the Stokes’ state of quiescent past and their implementation within the framework of a 3-D time domain BEM formulation for linear elastodynamics is discussed. Of particular interest are simplified time and space integrations of the above fundamental solutions. The accuracy as well as the efficiency of such computations are tested through comparison studies against other more computationally intense BEM techniques.