Browsing by Author "Liou, Gin-Show"

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Calculation of impedances for axial symmetric foundation embedded in half-space medium using solutions for one layer stratum
(2013)
Chung, Ie-Lung
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Liou, Gin-Show
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土木工程學系
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Department of Civil Engineering
The paper is devoted to develop a new scheme to calculate impedance matrices for axial-symmetric foundations embedded in half-space medium. The half-space medium can be approximated by increasing thickness of one layer stratum on rigid bedrock due to the effect of material damping. However, as thickness increases, the numerical problem will arise. This problem is caused by the numerical contamination by some negligible reflection waves from rigid bedrock. In reality, the effect of these reflection waves on impedance is getting small as the thickness of the one layer stratum increases. Therefore, the scheme will employ the solutions for one layer stratum with suppressing these reflection waves to generate the impedance for the case of half-space. The numerical results by the presented scheme are compared with the results by other scheme in order to show that the new numerical scheme is effective and the solutions in layered medium can be extended to obtain the results for the cases of layered half-space medium. Some numerical results of torsional, vertical, horizontal, coupling and rocking impedances with different embedded depths will be presented and comments on the numerical scheme will be given.
Compressive behavior of dual-gusset-plate connections for buckling-restrained braced frames
(2012-09-01)
Chou, Chung-Che
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Liou, Gin-Show
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Yu, Jiun-Chi
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土木工程學系
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Department of Civil Engineering
This work conducts compression tests and finite element analyses for steel dual-gusset-plate connections used for buckling-restrained braced frames (BRBFs). Compared to a single-gusset-plate connection, dual gusset plates sandwiching a BRB core reduce gusset plate size, eliminate the need for splice plates, and enhance connection stability under compression. The experimental program investigated ultimate compression load by testing ten large dual-gusset-plate connections. Out-of-plane deformation of the gusset plate in the test resembled that of a buckled gusset plate with low bending rigidity provided by the BRB end. The general-purpose nonlinear finite element analysis program ABAQUS was applied for correlation analysis. A parametric study of the dual-gusset-plate connection was performed to study the effects of plate size, presence of centerline stiffeners, and beam and column boundaries on ultimate compression load. The ultimate compression load of the dual-gusset-plate connection could not be predicted based on the AISC-LRFD approach due to beam flange out-of-plane deformation. The ultimate compression load of the dual-gusset-plate connection was reasonably predicted using a column strip length from the Whitmore section to the workpoint of the beam and column centerlines and a buckling coefficient of K = 2. (C) 2012 Elsevier Ltd. All rights reserved.
Further investigation of vibration induced by harmonic loadings applied at circular rigid plate on half-space medium
(2011-10-01)
Liou, Gin-Show
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土木工程學系
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Department of Civil Engineering
This article is the further investigation of vibration induced by harmonic loadings applied at a circular rigid plate on a half-space medium as reported by Liou (Liou, G.S., 2009. Vibrations induced by harmonic loadings applied at circular rigid plate on half-space medium. Journal of Sound and Vibration, 323, 257-269). The main purposes of this article are (1) to give the semi-analytic solution for vibration at any specific location in half-space medium; (2) to calculate the total average energy flux over one period of vibration time from the surfaces of a cylindrical cavity. The reason to evaluate the total average energy flux is that the fluctuation phenomenon of vibration amplitude along the distance from the vibration source (circular rigid plate) has been observed by Liou (2009) and can be seen from the numerical results in this article. To calculate the total average energy flux from the surfaces, piecewise linear distribution of energy flux intensity along z-direction for cylindrical surface and r-direction for bottom surface of the cylindrical cavity is assumed. The results show that the total average energy flux from the surfaces attenuates as distance from vibration source increases. This is due to the material damping in the half-space medium. The attenuation of total average energy flux is faster as the damping in the half-space medium is higher.
Impedance matrices for circular foundation embedded in layered medium
(2009-04-01)
Liou, Gin-Show
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Chung, I. L.
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土木工程學系
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Department of Civil Engineering
A numerical scheme is developed in the paper for Calculating torsional, vertical, horizontal, coupling and rocking impedances in frequency domain for axial-symmetric foundations embedded in layered media. In the scheme, the whole soil domain is divided into interior and exterior domains. For the exterior domain, the analytic solutions with unknown coefficients are obtained by solving three-dimensional (31)) wave equations in cylindrical coordinates satisfying homogeneous boundary conditions. For the interior domain, the analytical solutions are also obtained by solving the same 3D wave equations satisfying the homogeneous boundary conditions and the prescribed boundary conditions. The prescribed conditions are the interaction tractions at the interfaces between embedded foundation and surrounding soil. The interaction tractions are assumed to be piecewise linear. The piecewise linear tractions at the bottom surface of foundation will be decomposed into a series of Bessel functions which can be easily fitted into the general solutions of wave equations in cylindrical coordinates. After all the analytic solutions with unknown coefficients for both interior and exterior domains are found, the variational principle is employed using the continuity conditions (both displacements and stresses) at the interfaces between interior and exterior domains, interior domain and foundation, and exterior domain and foundation to find impedance functions. Some numerical results of torsional. vertical, horizontal, coupling and rocking impedances with different embedded depths will be presented and comments on the numerical scheme will be given. (c) 2008 Elsevier Ltd. All rights reserved.
Internal flange stiffened moment connections with low-damage capability under seismic loading
(2013-08-01)
Chou, Chung-Che
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Lo, Sheng-Wei
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Liou, Gin-Show
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土木工程學系
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Department of Civil Engineering
This study presents the seismic performance of steel moment connections using internal flange stiffeners (IFSs) welded at the face of the wide-flange column and inner side of the beam flange. The objective is to develop a steel moment connection that can achieve good seismic performance with low-damage capability during a large earthquake loading and minimize the repair cost. Four large-scale moment connections were tested to validate the cyclic performance. One connection which represented a welded-unreinforced flange-bolted web connection failed before finishing cyclic tests at a drift of 4%. Three IFS moment connections showed excellent performance and low damage after experiencing the AISC seismic load twice up to the target drift of 4%, without strength reduction. The specimens were also modeled using the computer program ABAQUS to further verify the effectiveness of the IFS in transferring beam moment to the column and to investigate potential sources of connection failure. (C) 2013 Elsevier Ltd. All rights reserved.
Solutions for Distributed Harmonic Loadings on Axially Symmetric Area in Layered Half-space
(2014-01-01)
Liou, Gin-Show
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土木工程學系
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Department of Civil Engineering
The paper is to solve the problem of the response of stratified half-space subjected to an triangularly distributed time-harmonic loadings on an axial symmetric area buried in the stratified half-space. Since the distributed area can be very small, the solution can be employed to deal with the problems of elastodynamic using the fundamental solution method. The advantage of the presented solution over Green function is that singularity situation will not occur in the presented solution. Some numerical results are given and some conclusions are made. The presented solution is very efficient in computation.
VIBRATIONS INDUCED BY HARMONIC LOADINGS APPLIED AT CIRCULAR PLATE ON LAYERED MEDIUM
(2013-06-01)
Liou, Gin-Show
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土木工程學系
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Department of Civil Engineering
A systematic procedure is developed to calculate ground vibration at any specific location in layered medium due to harmonic loadings applied at a circular plate on the medium. In the procedure, the technique decomposing the interaction tractions between excited plate and layered medium will be employed. The decomposed tractions will automatically match boundary values of general solutions of three dimensional wave equations in cylindrical coordinates. In numerical results, the effect of layered stratum on ground vibration will be investigated and how ground vibration in layered medium decreases with depth will be presented. Also, from the numerical results, one can observe ground vibration may not decay monotonically along distance away from vibration source. The presented scheme is proved to be effective and efficient for accurately predicting near-field ground response to harmonic loadings applied at a rigid circular plate on layered medium. Comments on the presented scheme and numerical results will be given.
Vibrations induced by harmonic loadings applied at circular rigid plate on half-space medium
(2009-06-05)
Liou, Gin-Show
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土木工程學系
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Department of Civil Engineering
The paper presents a systematic scheme to calculate the vibration at any specific location oil a half-space medium Clue to harmonic vibrations of a circular rigid plate on the medium. In the scheme, the analytic solutions of 3D wave equations ill cylindrical coordinates are employed. The vibration at any specific location on lialf-space medium is obtained analytically by a semi-infinite integration with respect to wave number k from 0 to infinity. Because of decaying nature of integrand with respect to wave number k(u) the numerical integration can only be performed up to a certain upper limit k(u) instead of Go without loosing accuracy. The choosing of the integration tipper limit k(u) is dependent upon the factors of nondimensional vibration frequency and nondimensional distance between vibration source and receiving location. From the numerical results, one finds that some components of vibration on the surface may not attenuate monotonically along the distance from source. Some verification for the accuracy of the presented scheme will be made, and selected numerical results will be shown and discussed. Comments oil the presented scheme will be given, and the presented scheme is proved to be effective and efficient for accurately predicting the vibrations oil the surface induced by harmonic loadings applied at rigid circular plate. (C) 2009 Elsevier Ltd. All rights reserved.