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CONTENTS
Volume 18, Number 2, August 2004
 

Abstract
The optimization of active bars?placement and feedback gains of closed loop control system for random intelligent truss structures under non-stationary random excitation is presented. Firstly, the optimal mathematical model with the reliability constraints on the mean square value of structural dynamic displacement and stress response are built based on the maximization of dissipation energy due to control action. In which not only the randomness of the physics parameters of structural materials, geometric dimensions and structural damping are considered simultaneously, but also the applied force are considered as non-stationary random excitation. Then, the numerical characteristics of the stationary random responses of random intelligent structure are developed. Finally, the rationality and validity of the presented model are demonstrated by an engineering example and some useful conclusions are obtained.

Key Words
optimization; non-stationary random excitation; random intelligent truss structures; reliability constraints; active bars\' placement; feedback gains.

Address
W. Gao, J. J. Chen and T. B. Hu; School of Electromechanical Engineering, Xidian University, Xi\'an, 710071, P. R. China
N. J. Kessissoglou and R. B. Randall; School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, NSW2052, Australia

Abstract
The interaction between concrete core expansion and deformation of perimeter ties has been known to have a significant effect on the effective confinement of rectangular reinforced concrete (RC) tied columns. This interaction produces passive confining pressure to the concrete core. Most existing models for determining the response of RC tied columns do not directly account for the influence of flexural stiffness of the ties and the variation of confining stress along the column height. This study presents a procedure for determining the confined compressive strength of RC square columns confined by rectilinear ties with various tie configurations considering directly the influence of flexural flexibility of the ties and the variation of confining stress along the vertical direction. The concept of area compatibility is employed to ensure compatibility of the concrete core and steel hoop in a global sense. The proposed procedure yields satisfactory predictions of confined strengths compared with experimental results, and the influence of tie flexibility, tie configuration and degree of confinement can be well captured.

Key Words
reinforced concrete columns; confinement; flexural flexibility; rectilinear ties; tie configurations.

Address
J. Teerawong, P. Lukkunaprasit and T. Senjuntichai;
Dept. of Civil Engineering, Chulalongkorn University, Bangkok 10330, Thailand

Abstract
In this paper axial loading tests on low strength concrete members, which were confined with various thickness of carbon fiber reinforced polymer (CFRP) composite sheets are described. Totally 46 specimens with circular, square and rectangular cross-sections with unconfined concrete compressive strengths between 6 and 10 MPa were included in the test program. During the tests, a photogrammetrical deformation measurement technique was also used, as well as conventional measurement techniques. The contribution of external confinement with CFRP composite sheets to the compressive behavior of the specimens with low strength concrete is evaluated quantitatively, in terms of strength, longitudinal and lateral deformability and energy dissipation. The effects of width/depth ratios and the corner radius of the specimens with rectangular cross-section on the axial behavior were also examined. It was seen that the effectiveness of the external confinement with CFRP composite sheets is much more pronounced, when the unconfined concrete compressive strength is relatively lower. It was also found that the available analytical expressions proposed for normal or high strength concrete confined by CFRP sheets could not predict the strength and deformability of CFRP confined low strength concrete accurately. New expressions are proposed for the compressive strength and the ultimate axial strain of CFRP confined low strength concrete.

Key Words
compression; concrete; confined concrete; ductility; fibers; stress-strain curves.

Address
Alper Ilki, Nahit Kumbasar and Volkan Koc;
Istanbul Technical University, Civil Eng. Faculty, 34469, Maslak, Istanbul, Turkey

Abstract
By means of the two-dimensional basic equations of transversely isotropic magneto-electro-elastic media and the strict differential operator theorem, the general solution in the case of distinct eigenvalues is derived, in which all mechanical, electric and magnetic quantities are expressed in four harmonic displacement functions. Based on this general solution in the case of distinct eigenvalues, a series of problems is solved by the trial-and-error method, including magneto-electro-elastic rectangular beam under uniform tension, electric displacement and magnetic induction, pure shearing and pure bending, cantilever beam with point force, point charge or point current at free end, and cantilever beam subjected to uniformly distributed loads. Analytical solutions to various problems are obtained.

Key Words
general solution; magneto-electro-elastic plane; harmonic function; analytical solution.

Address
Aimin Jiang; West Branch of Zhejiang University of Technology, Quzhou 324006, P.R. China
Haojiang Ding; Department of Civil Engineering, Zhejiang University, Hangzhou 310027, P.R. China

Abstract
The main purpose of this paper is the numerical analysis of the non-linear seismic response of a RC building mock-up. The mock-up is subjected to different synthetic horizontal seismic excitations. The numerical approach is based on a 3D-model involving multilayered shell elements. These elements are composed of several single-layer membranes with various eccentricities. Bending effects are included through these eccentricities. Basic equations are first written for a single membrane element with its own eccentricity and then generalised to the multilayered shell element by superposition. The multilayered shell is considered as a classical shell element : all information about non-linear constitutive relations are investigated at the local scale of each layer, whereas balance and kinematics are checked afterwards at global scale. The non-linear dynamic response of the building is computed with Newmark algorithm. The numerical dynamic results (blind simulations) are considered in the linear and non linear cases and compared with experimental results from shaking table tests. Multilayered shell elements are found to be a promising tool for predictive computations of RC structures behaviour under 3D seismic loadings. This study was part of the CAMUS International Benchmark.

Key Words
structural dynamics; non linear seismic response; multilayered shells; 3D modeling; finite element method.

Address
J. F. Semblat; Laboratoire Central des Ponts et Chaussees (LCPC), Eng. Modeling Department, 58 bd Lefebvre, 75732 PARIS Cedex 15, France
A. Aouameur; Dassault Data Services, Formerly at Laboratoire Central des Ponts et Chaussees (LCPC), France
F. J. Ulm; Massachusetts Institute of Technology, Cambridge, USA

Abstract
In this paper, a comparison of various random vibration and deterministic dynamic analyses of cable-stayed bridges subjected to asynchronous ground motion is presented. Different random vibration methods are included to determine the dynamic behaviour of a cable-stayed bridge for various ground motion wave velocities. As a numerical example the Jindo Bridge located in South Korea is chosen and a 413 DOF mathematical model is employed for this bridge. The results obtained from a spectral analysis approach are compared with those of two random vibration based response spectrum methods and a deterministic method. The analyses suggest that the structural responses usually show important amplifications depending on the decreasing ground motion wave velocities.

Key Words
spectral analysis approach; multiple support response spectrum method; deterministic analysis; asynchronous ground motion; cable-stayed bridge.

Address
K. Soyluk; Department of Civil Engineering, Gazi University, Maltepe, Ankara 06570, Turkey
A. A. Dumanoglu; Grand National Assembly of Turkey, Ankara, Turkey
M. E. Tuna; Department of Architecture, Gazi University, Maltepe, Ankara 06570, Turkey

Abstract
In the earlier application of the spline finite strip method(FSM), the uniform B3-spline functions were used in the longitudinal direction while the conventional interpolation functions were used in the transverse direction to construct the displacement filed in a strip. To overcome the shortcoming of the uniform B3-spline, non-periodic B-spline was developed as the displacement function. The use of non-periodic B3-spline function requires no tangential vectors at both ends to interpolate the geometry of shell and the Kronecker delta property is also satisfied at the end boundaries. Recently, non-periodic spline FSM which was modified to have a multiple knots at the boundary was developed for the shell analysis and applied to the analysis of bridges. In the formulation of a non-symmetric spline finite strip method, the concepts of non-periodic B3-spline and a stress-resultant finite strip with drilling degrees of freedom for a shell are used. The introduction of non-symmetrically spaced knots in the longitudinal direction allows the selective local refinement to improve the accuracy of solution at the connections or at the location of concentrated load. A number of numerical tests were performed to prove the accuracy and efficiency of the present study.

Key Words
non-periodic B-spline function; stress-resultant shell; a non-symmetric spline finite strip method.

Address
Kyeong-Ho Kim; Chungsuk Engineering Specific, Structural Division,
57 Karak-dong, Songpa-gu, Seoul, Korea
Chang-Koon Choi; Department of Civil and Environmental Engineering, KAIST, Daejeon 373-1, Korea

Abstract
The purpose of this paper is to determine the subsoil depth affected from the load on the plate resting on elastic foundation using stress distribution within the subsoil that will be occurred depending on the loading and dimension of the plate. An iterative method is developed in order to determine the effective depth of the subsoil under the plate. Numerical examples from the technical literature are solved by means of the method suggested herein and displacements, bending moments and shear forces are presented in graphical and tabular forms to evaluate the effects of the limit depth considered in the study. Results showed the efficiency and simplicity of the present approach for the plate resting on an elastic foundation.

Key Words
effective depth; plates on elastic foundation; Winkler model; Vlasov model; parameters of soil.

Address
Ayse T. Daloglu and K. Ozgan; Department of Civil Engineering, Karadeniz Technical University, Trabzon, 61080, Turkey


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