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CONTENTS
Volume 25, Number 5, March30 2007
 

Abstract
In this work, a new approach is developed for dynamic analysis of a composite beam with an interply crack, based on finite element solution of partial differential equations with the use of the COMSOL Multiphysics package, allowing for fast and simple change of geometric characteristics of the delaminated area. The use of COMSOL Multiphysics package facilitates automatic mesh generation, which is needed if the problem has to be solved many times with different crack lengths. In the model, a physically impossible interpenetration of the crack faces is prevented by imposing a special constraint, leading to taking account of a force of contact interaction of the crack faces and to nonlinearity of the formulated boundary value problem. The model is based on the first order shear deformation theory, i.e., the longitudinal displacement is assumed to vary linearly through the beam\'s thickness. The shear deformation and rotary inertia terms are included into the formulation, to achieve better accuracy. Nonlinear partial differential equations of motion with boundary conditions are developed and written in the format acceptable by the COMSOL Multiphysics package. An example problem of a clamped-free beam with a piezoelectric actuator is considered, and its finite element solution is obtained. A noticeable difference of forced vibrations of the delaminated and undelaminated beams due to the contact interaction of the crack\'s faces is predicted by the developed model.

Key Words
composite delaminated beam; contact of crack faces; shear deformation theory; nonlinear partial differential equations; nonlinear finite element analysis; COMSOL Multiphysics package; automatic mesh generation.

Address
University of Dayton Research Institute, 6130 Noranda Dr., Dayton, Ohio 45415, USA

Abstract
In this paper, the energy-based plastic-damage model previously proposed by the authors [International Journal of Solids and Structures, 43(3-4): 583-612] is first simplified with an empirically defined evolution law for the irreversible strains, and then it is extended to its rate-dependent version to account for the strain rate effect. Regarding the energy dissipation by the motion of the structure under dynamic loadings, within the framework of continuum damage mechanics a new damping model is proposed and incorporated into the developed rate-dependent plastic-damage mode, leading to a unified constitutive model which is capable of directly considering the damping on the material scale. Pertinent computational aspects concerning the numerical implementation and the algorithmic consistent modulus for the unified model are also discussed in details, through which the dynamic nonlinear analysis of damping structures can be coped with by the same procedures as those without damping. The proposed unified plastic-damage model is verfied by the simulations of concrete specimens under different quasistatic and high rate straining loading conditions, and is then applied to the Koyna dam under earthquake motions. The numerical predictions agree fairly well with the results obtained from experimental tests and/or reported by other investigators, demonstrating its capability for reproducing most of the typical nonlinear performances of concrete under quasi-static and dynamic loading conditions.

Key Words
concrete; continuum damage mechanics; nonlinear analysis; dynamics; damping.

Address
Jian-Ying Wu; Dept. of Civil Engineering, South China Univ. of Technology, Guangzhou,Post code: 510640, P.R. China
Jie Li; Dept. of Building Engineering, Tongji University, Shanghai, Post code: 200092, P.R. China

Abstract
This paper investigates the feasibility of supplementing base isolation with active bang-bang control mechanisms. We formulate discrete approximations to energy-balance and power-demand equations for a base isolated structure supplemented with constant stiffness bang-bang (CKBB) control. Numerical experiments are conducted to: (1) Identify situations when constant stiffness bang-bang control is most likely to \"add value\" to system responses due to base isolation alone, and (2) Quantitatively determine the work done and power required by the actuators. A key observation from the numerical experiments is that \"overall performance\" of the actuators is coupled to \"input energy per unit time.\"

Key Words
base isolation; bang-bang control; energy-based design.

Address
Dept. of Civil and Environmental Engineering, and Institute for Systems Research,University of Maryland, College Park, MD 20742, USA

Abstract
The article describes a technique for the measurement of the level of complexity of fracture surfaces by the method of vertical sections, and a performed statistical analysis of the effect of profile lines on the fractographic and fractal parameters of fractures, i.e. the profile line development factor, RL, and the fracture surface development factor, RS, (as defined by the cycloid method), as well as the fractal dimension, DC, (as determined by the chord method), and the fractal dimension, DBC, (as determined by the box method). The above-mentioned parameters were determined for fracture surfaces of basalt and gravel concretes, respectively, which had previously been subjected to fracture toughness tests. The concretes were made from mixtures of a water/cement ratio ranging from 0.41 to 0.61 and with a variable fraction of coarse aggregate to fine aggregate, Cagg./Fagg., in the range from 1.5 to 3.5. Basalt and gravel aggregate of a fraction to maximum 16 mm were used to the tests. Based on the performed analysis it has been established that the necessary number of concrete fracture profile lines, which assures the reliability of obtained testing results, should amount to 12.

Key Words
concrete; fractal dimension; pores structure; image analysis.

Address
Rzeszow University of Technology, Powstancow Warszawy 6, 35-959 Rzeszow, Poland

Abstract
Recent development of fiber optic sensor technology has provided an excellent choice for civil engineers for performance monitoring of civil infrastructures. Fiber optic sensors have the advantages of small dimensions, good resolution and accuracy, as well as excellent ability to transmit signal at long distances. They are also immune to electromagnetic and radio frequency interference and may incorporate a series of interrogated sensors multiplexed along a single fiber. These advantages make fiber optic sensors a better method than traditional damage detection methods and devices to some extent. This paper provides a review of recent developments in fiber optic sensor technology as well as some applications of fiber optic sensors to the performance monitoring of civil infrastructures such as buildings, bridges, pavements, dams, pipelines, tunnels, piles, etc. Existing problems of fiber optic sensors with their applications to civil structural performance monitoring are also discussed.

Key Words
fiber optic sensors; performance monitoring; civil infrastructure; damage detection.

Address
Dept. of Civil and Environmental Engineering, Louisianan State University, Baton Rouge, LA 70803, USA

Abstract
Many works have been done in classical theory of thermoelasticity in materials with memory by researchers like Nunziato, Chen and Gurtine and many others. No work is located in generalized thermoelasticity regarding materials with memory till date. The present paper deals with the wave propagation in materials with memory in generalized thermoelasticity. Plane progressive waves and Rayleigh waves have been discussed in details. In the classical theory of heat conduction it was observed that heat propagates with infinite speed. This paradox has been removed in the present discussion. The set of governing equations has been developed in the present analysis. The results of wave velocity and
attenuation coefficient corresponding to low and high frequency have been obtained. For thermal wave the results show appreciable differences with those in the usual thermoelasticity theory.

Key Words
generalized thermoelasticity; plane progressive waves; Rayleigh waves.

Address
Arup Baksi; Umes Chandra College 13, Surya Sen Street, Calcutta-700012, India
Bidyut Kumar Roy; Department of Mathematics, Vivekananda College, 269, D. H. Road, Calcutta-700063, India
Rasajit Kumar Bera; Heritage Institute of Technology, Chowbaga Road, Anandapur, P.O. East Kolkata Township,
Kolkata-700107, India

Abstract
A finite element method (FEM) of B-spline wavelet on the interval (BSWI) is used in this paper to solve the static and vibration problems of thin plate. Instead of traditional polynomial interpolation, the scaling functions of two-dimensional tensor product BSWI are employed to construct the transverse displacements field. The method combines the accuracy of B-spline functions approximation and various basis functions for structural analysis. Some numerical examples are studied to demonstrate the proposed method and the numerical results presented are in good agreement with the solutions of other methods.

Key Words
B-spline wavelet on the interval; finite element method; thin plate analysis; modal analysis.

Address
Jiawei Xiang; School of Mechantronic Engineering, Guilin University of Electronic Technology, Guilin 541004, P.R. China
Zhengjia He, Yumin He and Xuefeng Chen; School of Mechanical Engineering, Xi\'an Jiaotong University, Xi\'an 710049, P.R. China

Abstract
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Key Words
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Address
J. Zhang; Dept. of Structural Engineering, Univ. of California, San Diego, 9500 Gilman Drive, MC 0085 LA Jolla, CA 92093-0085, USA
T. Sato; Section of Disaster Management and Social Service, Kobegakuin University, Kobe 651-2180, Japan
S. Iai; Dept. of Civil and Earth Resources Engineering, Kyoto University, Kyoto, 611-0011, Japan


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