Browsing by Author "Liou, GS"

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Comparison of time domain BEM for 2D elastodynamic
(1998-07-01)
Wang, CC
;
Liou, GS
;
土木工程學系
;
Department of Civil Engineering
The three (LC, QC and QL) new time domain BEM methods are compared with each other and with an analytical method, the Laplace domain BEM method and another time domain boundary element method by solving two example problems of a circular cylindrical cavity subjected to a suddenly applied internal pressure, and a finite bar subjected to a ramp-step loading. Numerical study reveals that the three (LC, QC and QL) new methods are more accurate and stable than the other numerical methods used for comparison. Demonstration of the numerical computational time versus time steps of the three BEM methods is also given for a simple two-dimensional elastodynamics problem of a bar with 12-quadratic-element mesh due to an end traction. The difference in computational times by QC and LC methods is small.
Effect of slab flexibility on interaction between two circular foundations
(1996-06-01)
Liou, GS
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
;
Department of Civil Engineering
The paper is aimed at investigating the effect of foundation rigidity on dynamic stiffness for two circular foundations on a viscoelastic medium. To generate the dynamic stiffness, a substructure technique is employed. For the substructure of a viscoelastic medium, the solution for wave motion reported in Reference 11 is used. For the substructures of two flexible foundations, classical plate theory with the inertial force neglected is employed to find the displacement fields of the foundation plates subjected to the interaction stresses. Then, the continuity condition for all the substructures is imposed implicitly by using the variational principle; then with the help of the reciprocal theorem the dynamic stiffness for the two flexible foundations can be obtained. For the numerical study, the boundary condition at the rims of both foundation plates is assumed to be a hinge connection to superstructures. Some numerical investigations are performed and the effect of foundation rigidity on dynamic stiffness is examined. Some discussions and conclusions are also made.
Effect of slab flexibility on interaction between two circular foundations
(1996-06-01)
Liou, GS
;
土木工程學系
;
Department of Civil Engineering
The paper is aimed at investigating the effect of foundation rigidity on dynamic stiffness for two circular foundations on a viscoelastic medium. To generate the dynamic stiffness, a substructure technique is employed. For the substructure of a viscoelastic medium, the solution for wave motion reported in Reference 11 is used. For the substructures of two flexible foundations, classical plate theory with the inertial force neglected is employed to find the displacement fields of the foundation plates subjected to the interaction stresses. Then, the continuity condition for all the substructures is imposed implicitly by using the variational principle; then with the help of the reciprocal theorem the dynamic stiffness for the two flexible foundations can be obtained. For the numerical study, the boundary condition at the rims of both foundation plates is assumed to be a hinge connection to superstructures. Some numerical investigations are performed and the effect of foundation rigidity on dynamic stiffness is examined. Some discussions and conclusions are also made.
Numerical time domain BEM experiment for 2-D elastodynamics
(2003-09-01)
Liou, GS
;
Lai, GZ
;
Wang, CC
;
土木工程學系
;
Department of Civil Engineering
This paper investigates some numerical aspects of solving 2-D time domain elastodynamic problems by the Boundary Element Method. In the investigation, quadratic spatial elements on the boundaries of domains, and linear temporal variations for displacement and constant temporal variation for traction in one time step are employed. For calculating internal displacement and stress, the traction kernels and internal stress kernels are derived by following the methodology developed by Israil and Banerjee. Since the non-dimensional time step beta=c(1)Deltat/l is a major parameter in judging the accuracy and stability of time domain BEM, the effects of beta value on numerical results are examined thoroughly in the investigation. Also, how accurate the time dot, main BEM is for calculating internal stress and displacement is also investigated comprehensively. Some conclusions are drawn from numerical experiments.
Quadratic time domain BEM formulation for 2D elastodynamic transient analysis
(1997-01-01)
Wang, CC
;
Wang, HC
;
Liou, GS
;
土木工程學系
;
Department of Civil Engineering
An accurate and efficient time domain BEM for the 2D elastodynamic wave transient analysis method is presented. Emphasis is focused on developing time domain fundamental convoluted kernels and methodology for quadratic temporal solution procedures which have never been presented before. In the presented BEM method, called the QC method, the temporal variations of displacement and traction are assumed to be quadratic and constant, respectively. The spatial variations of displacement and traction fields are assumed to be quadratic. Also, the LC method, assuming linear temporal variation of displacement field and constant temporal variation of traction field, is examined in the paper. For the verification of the QC method, rectangular bars subject to different end loads are studied. The numerical results by the QC method are compared with analytical solutions and those by the LC method. Numerical study reveals that the QC method is more accurate and stable. In the QC method, a good numerical result can still be obtained even when beta=1.0-2.0. However beta=0.50-0.75 should be used in the LC method in order to obtain good numerical results. This would provide evidence that the QC method has great advantages over the LC method. Some conclusions regarding the QC method are also made. Copyright (C) 1996 Elsevier Science Ltd.
Response of a tunnel in soft ground to longitudinal earthquake excitations
(1995)
Liou, GS
;
Hwang, CY
;
土木工程學系
;
Department of Civil Engineering
Roles of non-structural walls in Chi-Chi Earthquake
(2002-07-01)
Liou, GS
;
Chiu, YF
;
Cheng, FP
;
土木工程學系
;
Department of Civil Engineering
Presented are some close observations of failure modes of building structures after the Chi-Chi Earthquake, which occurred on September 21, 1999, and some numerical analysis of building structures that proves the conclusions of these close observations. According to the observations and analysis results, one can conclude that non-structural walls play a major role in the damage and collapse of building structures in strong earthquakes. Therefore, some suggestions are made for the structural design industry and academic research in order to improve the earthquake resistance of existing and future building structures.
Structural analysis model for mat foundations
(1996-09-01)
Liou, GS
;
Lai, SC
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交大名義發表
;
土木工程學系
;
National Chiao Tung University
A simplified structural analysis model for mat foundations with grid floor beams as stiffeners is presented here. In the model, the Winkler type of subgrade reaction spring is assumed for the whole area under the mar foundation, and the yield-line theory of slab is used to lump the Winkler springs under slabs to the corresponding locations under the adjacent floor beams of the slabs. Therefore, each floor beam is now supported by springs with a segmentally linearly varied spring constant. The total analysis model for the mat foundation is then simplified to be a grid beam system on an elastic foundation with a segmentally linearly varied spring constant, and is subjected to loadings from the columns of the building structure. Some numerical comparisons with the results by a sophisticated finite-element model are made in order to demonstrate the effectiveness and efficiency of the presented analysis model.
Two-dimensional elastodynamic transient analysis by QL time-domain BEM formulation
(1996-03-30)
Wang, CC
;
Wang, HC
;
Liou, GS
;
土木工程學系
;
Department of Civil Engineering
A quadratic time-domain Boundary Element Method (BEM) for two-dimensional (2-D) elastodynamic transient wave analysis is presented. Emphasis is focused on developing time-domain fundamental convoluted kernels and methodology for quadratic temporal solution procedure which are never presented before. In the presented BEM method, the displacement temporal variation is assumed to be quadratic, the traction temporal variation is assumed to be linear (called QL method, a two-time-step piecewise continuity method), and the spatial variations are assumed to be quadratic variation. The QL method is compared with the LC method and the QC method by solving several example problems. Numerical study reveals that the QC and QL methods are more accurate and stable than the LC method, and the QL method is much better than the QC method for transient problems.