Pisidhi Karasudhi

Force at a point in the interior of a layered elastic half space

Abstract This study formulates, by the technique of integral transforms, the solution of a layered half space subjected to a concentrated force which may act either vertically or horizontally in the interior of the system. Accurate approximations of the reciprocals of the common denominators in the solution integrals are suggested in such a way that the latter are in standard closed forms and can be identified by two parts. The first part is the singular part of Mindlins solution which is singular at the point of application of the force, and the second is non-singular. The solutions for plane problems are also obtained in closed forms by performing appropriate integrations of the solutions for the corresponding three-dimensional cases.

Thai construction industry: Demand and projection

Thailand is fast becoming a newly industrializing country and, consequently, a large number of construction works are projected for the future. This study is an attempt to gain further insight into the demand for construction activities in Thailand. Three types of construction - residential, non-residential and ‘other’ (mainly public projects) - were considered. The demand function for each type of construction was estimated using regression analysis. Results indicate that rising per capita income, the ratio of consumer price index to the construction cost index, and population are the major determinants of demand for residential construction. The expansion of industrial production capacity and the ratio of corporate savings to the construction cost index are the most significant factors affecting the demand for non-residential construction. The demand of other construction is found to be largely a function of rising revenues of government and of public utilities. Further, projection results indicate that...

Quasi-static bending of a cylindrical elastic bar partially embedded in a saturated elastic half-space

Abstract This paper presents the quasi-static behavior of a circular cylindrical elastic bar which is partially embedded in a saturated elastic half-space. The bar is subjected to a lateral force and a moment at a top end. The material of the half-space is governed by Biots consolidation theory. The problem is decomposed into two systems; namely, an extended half-space and a fictitious bar with a Youngs modulus equal to the difference between the Youngs moduli of the real bar and the half-space. The governing equation, which is formulated under the approximation that the slope of the fictitious bar is equal to the corresponding average over a circular area in the extended half-space, is found to be a Fredholm integral equation of the second kind, and solved by an appropriate numerical method for initial and final solutions.

Torsion of a long cylindrical elastic bar partially embedded in a layered elastic half space

Abstract This is a study of the axially symmetric torsion of a long elastic cylindrical bar which is embedded in a layered elastic half space. The stress singularity factor at the embedded end of the bar is estimated by an existing method, and its effects on the solution are investigated. Such effects are found to be not so significant, especially for long bars and when the main concern is only on the torque-twist angle relationship. Even for rather short bars, the results given by this study agree well with those by an existing method, which is more rigorous but restrictive only to the case of an infinitely rigid bar.

An efficient elastodynamic infinite element

Abstract An efficient elastodynamic infinite element capable of propagating Rayleigh waves and body waves in a homogeneous half-space is presented. The displacement interpolation functions are presented in convenient explicit forms by formulating the infinite element with respect to a spherical coordinate system. The infinite integrals appearing in the impedance matrix of an infinite element are integrated analytically which results in a drastic reduction in computation cost. These infinite elements are used to model the far field of a homogeneous half-space, while the near field is modelled by conventional finite elements. The applicability and accuracy of the proposed scheme are confirmed by solving several examples.

Singular stress fields of angle-ply and monoclinic bimaterial wedges

The characteristic equations for the order of stress singularity of anisotropic bimaterial wedges subjected to traction boundary conditions are investigated. For an angle-ply bimaterial wedge, both fully bonded and frictional interfaces are considered, whereas for a monoclinic bimaterial wedge, a frictional interface is considered. Here, the Stroh formalism and the separation of variables technique are used. In general, the order of stress singularity can be real or complex, but for the special geometry of a crack along the frictional interface of a monoclinic composite, it is always real. Explicit characteristic equations for the order of singularity are presented for an aligned orthotropic composite with a frictional interface. Numerical results are given for an angle-ply bimaterial wedge and a monoclinic bimaterial wedge consisting of a graphite/epoxy fiber-reinforced composite.

Seismic analysis of asymmetric building-foundation systems

Abstract A method of analysis for the earthquake response of three-dimensional multi-storey asymmetric buildings founded on a flexible foundation is presented. The building-foundation system considered in this study is a linear N -storey asymmetric building on a rigid footing resting on the surface of a linear elastic half-space. The whole system has 3 N + 5 displacement degrees of freedom. The governing equations are developed considering the motions of each floor and the motions of the whole system. The governing equations of the floors are first uncoupled in terms of footing displacements using the mode superposition method. Substitution of structural deformations, in combination with the dynamic soil-structure interaction force-displacement relationships proposed by Veletsos and Verbic [ ASCE J. Engng Mech. Div. 100, 189–201 (1974)]and Veletsos and Nair [ ASCE J. Geotechn. Engng Div. 100, 225–246 (1974)]into the governing equations of the whole system results in five integro-differential equations for footing displacements, which are then solved by numerical step-by-step time-history analysis. A 10-storey asymmetric building on soft soil was subjected to an artificially generated earthquake excitation in order to obtain the soil-structure interaction and eccentricity effects. The results show that soft soil conditions increase the lateral deflections, but reduce the twists, storey shears, and torques. Increasing eccentricity increases the twists and torques, but does not modify the lateral deflections at the centre of mass, and the total storey shears.

Stress Singularity Analysis of a Crack Terminating at the Interface of an Anisotropic Layered Composite

The order of stress singularities at the tip of an inclined crack terminating at the interface of an anisotropic layered composite is investigated. Both fully bonded and frictional interfaces are considered. The expressions for stresses and displacements are obtained by using the Stroh formalism. The stresses at the crack tip are expressed in the form σ ij = r -k F ij (θ), where k is the crack-tip singularity The singularity k is obtained by solving a characteristic equation which incorporates the effects of the interface and the crack faces. The problem can be visualized as two wedges created by a crack, pressing on a half-plane. For the frictional interface, depending on the relative slip directions of the two wedges, both the case of the two wedges slipping in opposite directions and the case of the two wedges slipping in the same direction are treated. In the numerical calculation of the singularities, a high modulus graphite/ epoxy layered composite is used and the effect of the crack inclination on the stress singularity k is graphically presented. In general, there are three roots of k for the fully bonded interface, while there are only two roots of k for the slipping interface.

Stress singularities of a crack terminating at the frictional interface of a monoclinic bimaterial composite

Abstract In this analysis, the order of stress singularities at the tip of an inclined crack terminating at the frictional interface of a monoclinic bimaterial composite is investigated. The expressions for stresses and displacements are obtained by using the Stroh formalism. The stresses at the crack tip are expressed in the form σij=r−kFij(θ), where k is the crack-tip singularity. In the formulation, the problem is visualized as two wedges created by a crack, pressing on a half-plane. Both the cases of the two wedges slipping in opposite directions and the case of the two wedges slipping in the same direction are considered. The characteristic equation to determine k which incorporates the effects of the interface, the crack faces and the relative slip directions of the two wedges is derived, in terms of the generalized Dundurs constants α and β, and the complex parameters p1 and p2 of both materials. For the special case when the crack is perpendicular to the interface of an orthotropic composite and the two wedges slip in opposite directions, the characteristic equation is reduced to two equations corresponding to mode I and mode II cracks. In the numerical calculations, a bimaterial graphite/epoxy composite with different fiber orientations is considered and the singularities are graphically presented.

Waves generated from fictitious focal points to match seismograms recorded

The ground domain is separated into a near field and a far field. The near field encompassing the fictitious focal point is discretized into finite elements. The far field is discretized into infinite elements. The shape functions of these infinite elements are in closed forms and with explicit compositions of constituent waves. The harmonic vibration analysis yields the Fourier transform of any constituent wave in terms of the amplitudes of the three orthogonal force components applied at the focal point, thus in terms of the Fourier transforms of the accelerations in three orthogonal directions recorded at a seismograph station. An appropriate inverse Fourier transform algorithm yields the transient constituent waves. All seismic waves at any points, inside the ground and on the ground surface, can be evaluated. The results can be more refined in case of the availability of simultaneous records at more seismograph stations. In case of two stations, we assume two fictitious focal points. Numerical examples of real site responses are presented by using one single focal point and two simultaneous focal points.