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CONTENTS
Volume 19, Number 5, March30 2005
 

Abstract
In this study, a new smart beam finite element is proposed for the finite element modeling of beam-type smart structures that are equipped with bonded plate-type piezoelectric sensors and actuators. Constitutive equations for the direct piezoelectric effect and converse piezoelectric effect of piezoelectric materials are considered in the formulation. By using a variational principle, the equations of motion for the smart beam finite element are derived. The proposed 2-node beam finite element is an isoparametric element based on Timoshenko beam theory. The proposed smart beam finite element is applied to the free vibration control adopting a constant gain feedback scheme. The electrical force vector, which is obtained in deriving an equation of motion, is the control force equivalent to that in existing literature. Validity of the proposed element is shown through comparing the analytical results of the verification examples with those of other previous researchers. With the use of smart beam finite elements, simulation of free vibration control is demonstrated by sensing the voltage of the piezoelectric sensors and by applying the voltages to the piezoelectric actuators.

Key Words
piezoelectric materials; piezoelectric sensor; piezoelectric actuator; Timoshenko beam theory; free vibration control.

Address
Myung-Kwan Song; Department of Civil Engineering, The University of Tokyo, Tokyo 113-8656, Japan
Hyuk-Chun Noh; Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027, U.S.A.
Sun-Hoon Kim; Department of Civil Engineering, Youngdong University, Chungbuk 370-701, Korea
In-Seon Han; Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea

Abstract
The parametric dynamic stability of an asymmetric sandwich beam with viscoelastic core on viscoelastic supports at the ends and subjected to an axial pulsating load is investigated. A set of Hill

Key Words
parametric dynamic instability; viscoelastic core; sandwich beam; viscoelastic supports; zone instability; simple and combination resonances.

Address
Ranajay Ghosh; Theoretical and Applied Mechanics, Cornell University, Ithaca, New York 14853-1503, USA
Sanjay Dharmavaram and Kumar Ray;
Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur-721302, India
P. Dash; A.T. - Bidyadharpur Sasam, P.O. Khaira, Dist., Orissa, Balasore-756048, India

Abstract
The numerical simulations on the influence of mesoscopic structures on the macroscopic strength and fracture characteristics are carried out based on that the concrete is assumed to be a three-phase composite composed of matrix (mortar), aggregate and bond between them by using a numerical code named MFPA. The finite element program is employed as the basic stress analysis tool when the elastic damage mechanics is used to describe the constitutive law of meso-level element and the maximum tensile strain criterion and Mohr-Coulomb criterion are utilized as damage threshold. It can be found from the numerical results that the bond between matrix and aggregate has a significant effect on the macroscopic mechanical performance of concrete.

Key Words
concrete; mesoscopic; fracture process; numerical simulation.

Address
Laboratory of Numerical Test on Material Failure, School of Resource and Civil Engineering, Box 138, Northeastern University, Shenyang 110004, China

Abstract
The non-linear static and dynamic response of doubly curved thin isotropic shells has been studied for the step and sinusoidal loadings. Dynamic analogues Von Karman-Donnel type shell equations are used. Clamped immovable and simply supported immovable boundary conditions are considered. The governing nonlinear partial differential equations of the shell are discretized in space and time domains using the harmonic differential quadrature (HDQ) and finite differences (FD) methods, respectively. The accuracy of the proposed HDQ-FD coupled methodology is demonstrated by the numerical examples. Numerical examples demonstrate the satisfactory accuracy, efficiency and versatility of the presented approach.

Key Words
non-linear dynamic analysis; doubly curved shells; harmonic differential quadrature; coupled methodology.

Address
Omer Civalek; Akdeniz University, Engineering Faculty, Civil Engineering Department, Division of Mechanics, 07200, Topcular, Antalya, Turkey
Mehmet Ulker; Firat University, Engineering Faculty, Civil Engineering Department, Division of Mechanics, Elazig, Turkey

Abstract
Using two different, but related approaches, an exact dynamic stiffness matrix for a two-part beam-mass system is developed from the free vibration theory of a Bernoulli-Euler beam. The first approach is based on matrix transformation while the second one is a direct approach in which the kinematical conditions at the interfaces of the two-part beam-mass system are satisfied. Both procedures allow an exact free vibration analysis of structures such as a plane or a space frame, consisting of one or more two-part beam-mass systems. The two-part beam-mass system described in this paper is essentially a structural member consisting of two different beam segments between which there is a rigid mass element that may have rotatory inertia. Numerical checks to show that the two methods generate identical dynamic stiffness matrices were performed for a wide range of frequency values. Once the dynamic stiffness matrix is obtained using any of the two methods, the Wittrick-Williams algorithm is applied to compute the natural frequencies of some frameworks consisting of two-part beam-mass systems. Numerical results are discussed and the paper concludes with some remarks.

Key Words
dynamic stiffness method; beam-mass systems; free vibration; Wittrick-Williams algorithm.

Address
School of Engineering and Mathematical Sciences, City University, London, Northampton Square, London, EC1V OHB, England, U.K.

Abstract
Numerous tests on concrete structure members under local pressure demonstrated that the compressive strength of concrete at the loaded surface is increased by the confinement effect provided by the enveloping concrete. Even though most design codes propose specific criteria for preventing bearing failure, they do not take into consideration size effect which is an important phenomenon in the fracture mechanics of concrete/reinforced concrete. In this paper, six series of square prism concrete blocks with three different depths (size range = 1:4) and two different height/depth ratios of 2 and 3 are tested under concentrated load. Ultimate loads obtained from the test results are analysed by means of the modified size effect law (MSEL). Then, a prediction formula, which considers effect of both depth and height on size effect, is proposed. The developed formula is compared with experimental data existing in the literature. It is concluded that the observed size effect is in good agreement with the MSEL.

Key Words
concrete; bearing strength; size effect law; modified size effect law.

Address
R. Ince; Firat University, Engineering Faculty, Civil Engineering Department, Elazig, Turkey
E. Arici; Firat University, Technical Education Faculty, Construction Education Department, Elazig, Turkey

Abstract
In this paper the accumulation of local damage during the cyclic loading in reinforced high-strength concrete columns is experimentally investigated. Two identical column specimens with annular cross-section and spiral reinforcement were designed and two tests, up to failure, under the action of a constant vertical concentrated force and a time-dependent concentrated horizontal force, were carried out at the LNEC shaking tables facility. Sine type signals, controlled in amplitude, frequency and time duration were used for these experiments. The concept of local damage based on local stiffness degradation is considered in detail and illustrated by experimental results. The specimens were designed and reinforced in such a way that the accumulation of damage was predicted by dominating deformations (cracking and crushing of the concrete) while the increasing of the loading values was a dominating factor of damage. It was observed that the local damage of HSC columns has exposed their anisotropic local behaviour. The damage accumulation was slightly different from the expected in accordance with the continuum damage concept, and a partial random character was observed.

Key Words
high-strength reinforced concrete; column specimen; shaking table; local damage; stiffness degradation.

Address
Rogerio Bairrao; Structures Department, National
Laboratory for Civil Engineering, Av. Brasil 101, 1700-066 Lisboa, Portugal
Rimantas Kaianauskas and Romualdas Kliukas;
Department Strength of Materials, Vilnius Gediminas Technical University, 11 Saul.etekio Ave, 10223 Vilnius-40, Lithuania


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