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CONTENTS
Volume 22, Number 1, January10 2006
 

Abstract
This paper presents a virtual boundary element-equivalent collocation method (VBEM) for the plane magnetoelectroelastic solids, which is based on the fundamental solutions of the plane magnetoelectroelastic solids and the basic idea of the virtual boundary element method for elasticity. Besides all the advantages of the conventional boundary element method (BEM) over domain discretization methods, this method avoids the computation of singular integral on the boundary by introducing the virtual boundary. In the end, several numerical examples are performed to demonstrate the performance of this method, and the results show that they agree well with the exact solutions. So the method is one of the efficient numerical methods used to analyze megnatoelectroelastic solids.

Key Words
magnetoelectroelastic solids; plane problem; virtual boundary element; fundamental solution; collocation method.

Address
Wei-An Yao and Xiao-Chuan Li;
State Key Laboratory of Structural Analysis for Institute Equipment, Dalian University of Technology, Dalian, 116023, P. R. China
Gui-Rong Yu; Department of Science, Shenyang Institute of Aeronautical Engineering, Shenyang, 110034, P. R. China

Abstract
The application of cellular materials in load-carrying and security-relevant structures requires the exact prediction of their mechanical behavior, which necessitates the development of robust simulation models and techniques based on appropriate experimental procedures. The determination of the yield surface requires experiments under multi-axial stress states because the yield behavior is sensitive to the hydrostatic stress and simple uniaxial tests aim only to determine one single point of the yield surface. Therefore, an experimental technique based on a uniaxial strain test for the description of the influence of the hydrostatic stress on the yield condition in the elastic-plastic transition zone at small strains is proposed and numerically investigated. Furthermore, this experimental technique enables the determination of a second elastic constant, e.g., Poisson\'s ratio.

Key Words
multi-axial testing; cellular solids; plasticity; yield surface; nonlinear behavior.

Address
T. Fiedler; Centre for Mechanical Technology and Automation, University of Aveiro, Aveiro, Portugal
A. Ochsner and J. Gracio;
Centre for Mechanical Technology and Automation, University of Aveiro, Aveiro, Portugal
Department of Mechanical Engineering, University of Aveiro, Aveiro, Portugal

Abstract
Three-dimensional description of building structure taking into consideration soil-structure interaction is a very complex problem and solution of this problem is often obtained by using finite element method. However, this method takes a significant amount of computational time and memory. Therefore, an efficient computational model based on subdivision of the structure into building elements such as wall and floor slab elements, plane and three-dimensional joints and lintels, that could provide accurate results with significantly reduced computational time, is proposed in this study for the analysis three-dimensional structures subjected to dynamic load. The examples prove the efficiency and the computing possibilities of the model.

Key Words
three-dimensional building elements; super elements; dynamic problem formulation; finite element method.

Address
Department of Civil Engineering, Bialystok University of Technology, ul. Wiejska 45E, 15-351 Bialystok, Poland

Abstract
The paper summarizes the dynamic-based assessment of a reinforced concrete arch bridge, dating back to the 50?. The outlined approach is based on ambient vibration testing, output-only modal identification and updating of the uncertain structural parameters of a finite element model. The Peak Picking and the Enhanced Frequency Domain Decomposition techniques were used to extract the modal parameters from ambient vibration data and a very good agreement in both identified frequencies and mode shapes has been found between the two techniques. In the theoretical study, vibration modes were determined using a 3D Finite Element model of the bridge and the information obtained from the field tests combined with a classic system identification technique provided a linear elastic updated model, accurately fitting the modal parameters of the bridge in its present condition. Hence, the use of output-only modal identification techniques and updating procedures provided a model that could be used to evaluate the overall safety of the tested bridge under the service loads.

Key Words
ambient vibration testing; arch bridge; enhanced frequency domain identification technique; finite element model updating; output-only modal identification; peak picking technique.

Address
Department of Structural Engineering, Politecnico di Milano, Milan, Italy

Abstract
This paper deals with the effects of various moisture environments on the structural behavior of concrete beams. The presented results were obtained within a large experimental program carried out at the Laboratoire Central des Ponts et ChaussŽes (LCPC), with Electricite de France (EDF) as a partner. The aim of this paper is to point out and to quantify the strains resulting from unidirectional moisture conditions: a drying gradient applied during 14 months, followed by the re-wetting of the dried surface during 9 months. The effect of reinforcement on the shrinkage and on the deformation due to water absorption is pointed out. Moreover, a lot of tests on companion cylinders and prisms were carried out to determine the mechanical characteristics of the material and help checking analysis methods. The paper focuses on numerous measurements obtained during the 23 months on one plain concrete beam and one reinforced concrete beam: variation of water content, followed by precise weighing and gammadensitometry, relative humidity measurements, local and global deformations in the three directions and deflection of the beams. Thus, the effects of drying and water absorption on the behavior of concrete structures are documented and analyzed in comparison with existing representation of water diffusion.

Key Words
concrete; reinforcement; moisture; shrinkage; water absorption.

Address
S. Multon; Laboratoire MatŽriaux et Durabilite des Constructions, 135, Avenue de Rangueil,31077 Toulouse Cedex 4, France
J-F. Seignol and F. Toutlemonde;
Laboratoire Central des Ponts et ChaussŽes, 58, Boulevard Lefebvre, 75732 Paris, Cedex 15, France

Abstract
Control of structural response due to seismic excitation in a manner of coupling adjacent buildings has been actively developed, and most attention focused on those buildings of similar height. However, with the rapid development of some modern cities, multi-story buildings constructed with an auxiliary low-rise podium structure to provide extra functions to the complex become a growing construction scheme. Being inspired by the positively examined coupling control approach for buildings with similar height, this paper aims to provide a comprehensive analytical study on control effectiveness of using friction dampers to link the two buildings with significant height difference to supplement the recent experimental investigation carried out by the writers. The analytical model of a coupled building system is first developed with passive friction dampers being modeled as Coulomb friction. To highlight potential advantage of coupling the main building and podium structure with control devices that provide a lower degree of coupling, the inherent demerit of rigid-coupled configuration is then evaluated. Extensive parametric studies are finally performed. The concerned parameters influencing the design of optimal friction force and control efficiency include variety of earthquake excitation and differences in floor mass, story number as well as number of dampers installed between the two buildings. In general, the feasibility of interaction control approach applied to the complex structure for vibration reduction due to seismic excitation is supported by positive results.

Key Words
coupling control; analytical study; passive friction damper; Coulomb friction; seismic excitation.

Address
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China

Abstract
The paper deals with the numerical solution of the dynamic problem of masonry structures. Masonry is modelled as a non-linear elastic material with zero tensile strength and infinite compressive strength. Due to the non-linearity of the adopted constitutive equation, the equations of the motion must be integrated directly. In particular, we apply the Newmark or the Hilber-Hughes-Taylor methods implemented in code NOSA to perform the time integration of the system of ordinary differential equations obtained from discretising the structure into finite elements. Moreover, with the aim of evaluating the effectiveness of these two methods, some dynamic problems, whose explicit solutions are known, have been solved numerically. Comparisons between the exact solutions and the corresponding approximate solutions obtained via the Newmark and Hilber-Hughes-Taylor methods show that in the cases under consideration both numerical methods yield satisfactory results.

Key Words
non-linear elasticity; masonry structures; dynamic analysis; finite element method.

Address
Istituto di Scienza e Tecnologie dell?nformazione ?. Faedo?STI-CNR Via G. Moruzzi, 1 56124 Pisa, Italy


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