Showing papers by "G. R. Dodagoudar published in 2008"

Seismic hazard assessment of Chennai city considering local site effects

Abstract: Chennai city suffered moderate tremors during the 2001 Bhuj and Pondicherry earthquakes and the 2004 Sumatra earthquake. After the Bhuj earthquake, Indian Standard IS: 1893 was revised and Chennai city was upgraded from zone II to zone III which leads to a substantial increase of the design ground motion parameters. Therefore, a comprehensive study is carried out to assess the seismic hazard of Chennai city based on a deterministic approach. The seismicity and seismotectonic details within a 100 km radius of the study area have been considered. The one-dimensional ground response analysis was carried out for 38 representative sites by the equivalent linear method using the SHAKE91 program to estimate the ground motion parameters considering the local site effects. The shear wave velocity profile was inferred from the corrected blow counts and it was verified with the Multichannel Analysis of Surface Wave (MASW) test performed for a representative site. The seismic hazard is represented in terms of characteristic site period and Spectral Acceleration Ratio (SAR) contours for the entire city. It is found that structures with low natural period undergo significant amplification mostly in the central and southern parts of Chennai city due to the presence of deep soil sites with clayey or sandy deposits and the remaining parts undergo marginal amplification.

Reliability analysis of reinforced soil walls under static and seismic forces

Abstract: The traditional factor of safety does not account for the variability and uncertainty of the different parameters considered in the analysis. On the other hand, the reliability approach considers t...

Two-dimensional modelling of contaminant transport through saturated porous media using the radial point interpolation method (RPIM)

Abstract: A new numerical tool is presented which models the two-dimensional contaminant transport through saturated porous media using a meshfree method called the radial point interpolation method (RPIM) with polynomial reproduction. In RPIM, an approximate solution is constructed entirely in terms of a set of nodes and no characterisation of the interrelationship of the nodes is needed. An advection-dispersion equation with sorption is considered to illustrate the applicability of the RPIM. The Galerkin weak form of the governing equation is formulated using two-dimensional meshfree shape functions constructed using thin plate spline radial basis functions. A computer program is developed for the implementation of the RPIM procedure. Three numerical examples are presented and the results are compared with those obtained from the analytical solution and finite element method. The experimental results are also used to validate the approach. The proposed RPIM has generated results with no oscillations and they are insensitive to Peclet constraints.

Seismic soil-structure interaction analysis of tall slender structures

Abstract: The seismic response of soil-structure system depends on the characteristics of the input motion, site conditions and structure itself. In a seismic soil-structure interaction analysis, it is necessary to consider the infinite extent and layered nature of the soil, and the nonlinear behaviour of soils. This paper presents the seismic soil-structure interaction (SSI) analysis of a ventilation stack located in a nuclear power plant site. The SSI analysis was carried out by the flexible volume substructure method using computer program SASSI 2000. The influence of various parameters such as relative stiffness of the layers of the site, thickness of soil layer and foundation embedment on the interaction behaviour of the stack is investigated. The nonlinear soil behaviour is modelled by using site-specific modulus reduction and damping ratio curves developed from the laboratory experiments. It is found that the seismic response at the various levels of the stack shows a strong dependence on the relati...

Meshfree modelling of 1d and 2d contaminant transport through saturated porous media

Abstract: This paper presents an alternative numerical tool to model the one—and two—dimensional contaminant transport through saturated porous media using a meshfree method called Element Free Galerkin Method (EFGM). In EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no characterization of the interrelationship of the nodes is needed. The advection-dispersion equation with sorption is considered to illustrate the applicability of EFGM. The unknown concentration values are approximated by using moving least-square approximants, which are constructed using a weight function, a linear basis function and a set of non-constant coefficients. The weak form of the governing equation is formulated and Lagrange multiplier method is used for enforcing the essential boundary conditions. Three numerical examples are presented and the results are compared with those obtained from the analytical and finite element results.

Two-dimensional Contaminant Transport Modelling Using Meshless Method

Abstract: This paper presents an alternative numerical method to model the two- dimensional contaminant transport through saturated porous media using a meshless method called Element Free Galerkin Method (EFGM). In EFGM, an approximate solution is constructed entirely in terms of a set of nodes and no elements or characterization of the interrelationship of the nodes is needed to construct the discrete equations. For analysis, the two-dimensional advection-dispersion equation with sorption is considered. The unknown concentration values are approximated by using moving least square approximants, which are constructed using a weight function, a linear basis function and a set of non-constant coefficients. A weak form of the governing equation is formulated and Lagrange multiplier method is used for enforcing the essential boundary conditions. MATLAB code is developed to obtain the numerical solution. Two numerical examples are presented to illustrate the applicability of the proposed method and the results are compared with those obtained from the finite element method.

A 2D contaminant transport model for unsaturated soils

Abstract: This paper presents a numerical model of two-dimensional (2D) contaminant transport through unsaturated porous media using a mesh-free method, called the radial point interpolation method (RPIM), with polynomial reproduction. A 2D form of the advection– dispersion equation, involving a reactive contaminant with linear first-order degradation, is considered in the analysis. In the RPIM, the Galerkin weak form is used to establish the system equation using 2D mesh-free shape functions constructed using thin plate spline radial-basis functions. A Matlab code is developed to obtain the numerical solution. Experimental results are used to validate the proposed RPIM. The applicability and performance of the RPIM are studied using three numerical examples. The results of the RPIM are compared with those obtained from the finite-element method. The RPIM has generated results with no oscillations, and which are insensitive to Peclet constraints.