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CONTENTS
Volume 5, Number 3, September 2012
 

Abstract
The concrete bridge is likely to produce fatigue cracks during long period of service due to the moving vehicular loads and the degeneration of materials. This paper deals with the time-frequency analysis of a coupled bridge-vehicle system. The bridge is modeled as an Euler beam with breathing cracks. The vehicle is represented by a two-axle vehicle model. The equation of motion of the coupled bridge-vehicle system is established using the finite element method, and the Newmark direct integration method is adopted to calculate the dynamic responses of the system. The effect of breathing cracks on the dynamic responses of the bridge is investigated. The time-frequency characteristics of the responses are analyzed using both the Hilbert-Huang transform and wavelet transform. The results of time-frequency analysis indicate that complicated non-linear and non-stationary features will appear due to the breathing effect of the cracks.

Key Words
bridge-vehicle system; dynamic response; time-frequency analysis; Hilbert-Huang transform; wavelet transform.

Address
W.J. Wang, Z.R. Lu and J.K. Liu: Department of Applied Mechanics, Sun Yat-sen University, Guangzhou, Guangdong Province, 510006, P.R. China

Abstract
Cable-stayed bridges are commonly used in modern bridge engineering for covering long spans. In some special cases, the designer is obliged to build such a bridge over an existing fault. Activation of this fault is possible to bring about a relative displacement or separation movement between two neighboring pylons of the bridge built on opposite sides of the fault. In this work, the effect of such a fault-induced pylon displacement on bridge

Key Words
cable-stayed bridges; pylon displacement; fault; fault induced pylon movement.

Address
I.G. Raftoyiannis, G.T. Michaltsos and T.G. Konstantakopoulos: Department of Civil Engineering, National Technical University of Athens, Greece

Abstract
This paper reports the development of a generalized inverse analysis formulation for the parameter estimation of four-parameter Burger model. The analysis is carried out by formulating the problem as a mathematical programming formulation in terms of identification of the design vector, the objective function and the design constraints. Thereafter, the formulated constrained nonlinear multivariable problem is solved with the aid of fmincon: an in-built constrained optimization solver module available in MatLab. In order to gain experience, a synthetic case-study is considered wherein key issues such as the determination and setting up of variable bounds, global optimality of the solution and minimum number of data-points required for prediction of parameters is addressed. The results reveal that the developed technique is quite efficient in predicting the model parameters. The best result is obtained when the design variables are subjected to a lower bound without any upper bound. Global optimality of the solution is achieved using the developed technique. A minimum of 4-5 randomly selected data-points are required to achieve the optimal solution. The above technique has also been adopted for real-time settlement of four oil refineries with encouraging results.

Key Words
inverse analysis; four-parameter Burger model; mathematical programming; constrained nonlinear multivariable problem; variable bounds; global optimality.

Address
Arindam Dey: Department of Civil Engineering, Indian Institute of Technology Guwahati, Assam-781039, India; Prabir Kr. Basudhar: Department of Civil Engineering, Indian Institute of Technology Kanpur, UP-208016, India

Abstract
Hygroexpansion of wood is a known and undesired characteristic in civil engineering. When wood is exposed to changing environmental humidity, it adsorbs or desorbs moisture and warps. The resulting distortions or - at restrained conditions - cracks are a major concern in timber engineering. We herein present a multiscale model for prediction of the macroscopic hygroexpansion behavior of individual pieces of softwood from their microstructure, demonstrated for spruce. By applying poromicromechanics, we establish a link between the swelling pressure, driving the hygroexpansion of wood at the nanoscale, and the resulting macroscopic dimensional changes. The model comprises six homogenization steps, which are performed by means of continuum micromechanics, the unit cell method and laminate theory, all formulated in a poromechanical framework. Model predictions for elastic properties of wood as functions of the moisture content closely approach corresponding experimental data. As for the hygroexpansion behavior, the swelling pressure has to be back-calculated from macroscopic hygroexpansion data. The good reproduction of the anisotropy of wood hygroexpansion, based on only a single scalar calibration parameter, underlines the suitability of the model. The multiscale model constitutes a valuable tool for studying the effect of microstructural features on the macroscopic behavior and for assessing the hygroexpansion behavior at smaller length scales, which are inaccessible to experiments. The model predictions deliver input parameters for the analysis of timber at the structural scale, therewith enabling to optimize the use of timber and to prevent moisture-induced damage or failure.

Key Words
wood; hygroexpansion; multilayered unit cell; microstructure; anisotropy; poromechanics; ray cells; earlywood; latewood.

Address
Stefan Gloimuller, Karin de Borst, Thomas K. Bader and Josef Eberhardsteiner: Institute for Mechanics of Materials and Structures, Vienna University of Technology, Karlsplatz 13/202, A-1040 Vienna, Austria

Abstract
In most of the design offices, analysis of the frame is carried out without considering the effect of the rigidity of mat. The analysis of the superstructure without modelling the foundation properly and conversely analysing the foundation system without considering the stiffness of the superstructure may mislead the estimation of the forces. This paper examines the parameters, which affect the interaction and they are grouped into relative stiffness factors krs and ksb. An interaction analysis is performed for the five storeyed space frame of 3 bays

Key Words
interaction; frame; mat; stiffness; settlement; forces; moments.

Address
D. Daniel Thangaraj: Civil Engineering, Anna University College of Engineering, Tindivanam-604 001, India; K. Ilamparuthi: Department of Civil Engineering, Anna University, Chennai-600 025, India

Abstract
We apply a partitioned-solution (iterative-staggered) coupling method based on a fixed Eulerian mesh with the level set function to a large-deformation fluid-structure interaction (FSI) problem where a large-deformable thin structure moves in a high-speed flow field, as an airbag does during deployment. This method combines advanced fluid and structure solvers−specifically, the constrained interpolation profile finite element method (CIP-FEM) for fluid Eulerian mesh and large-deformable structural elements for Lagrangian structural mesh. We express the large-deformable interface as a zero isosurface by the level set function, and introduce virtual nodes with level sets and structural normal velocities to generate the level set function according to the large-deformable interfacial geometry and enforce the kinematic condition at the interface. The virtual nodes are located in the direction normal to the structural mesh. It is confirmed that application of the method to unfolded airbag deployment simulation shows the adequacy of the method.

Key Words
fluid-structure interaction; large deformation; Eulerian mesh; level set function; interface treatment; partitioned-solution method.

Address
Gaku Hashimoto: The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan; Kenji Ono: RIKEN, 7-1-26 Minatojima-minami-machi, Chuo-ku, Kobe, Hyogo, 650-0047 Japan; Hiroshi Okuda: The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568, Japan


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