Techno Press
Tp_Editing System.E (TES.E)
Login Search


sem
 
CONTENTS
Volume 15, Number 6, June 2003
 

Abstract
Mechanical anchorage devices are generally tested in the laboratory and may be analyzed using the finite element method. These devices are composed of many components interacting through diverse contact interfaces. Generally, a Coulomb friction law is sufficient to take into account friction between smooth surfaces. However, in the case of mechanical anchorages, a gripping system, named herein the wedge-tendon system, is used to anchor the prestressing tendon. The wedge inner surface is made of a series of triangular notches designed to grip the tendon. In this particular case, the Coulomb law is not adapted to simulate the contact interface. The present paper deals with a new constitutive contact/gripping law to simulate the gripping effect. A parameter identification procedure, based on experimental results as well as on a finite element/neural network approach, is presented. It is demonstrated that all parameters have been selected in a satisfactory way and that the proposed constitutive law is well adapted to simulate the wedge gripping effect taking place in a mechanical anchorage device.

Key Words
anchorage device; contact; finite element; neural networks; parameter identification; wedge-tendon interface.

Address
Department of Applied Sciences, Universite du Quebec a Chicoutimi, Quebec, Canada, G7H 2B1
Department of Civil Engineering, Laval University, Quebec, Canada, G1K 7P4

Abstract
Current design specifications prescribe that the upper and lower reinforcement mat is required in the same amount to resist negative and positive moment in bridge decks. This design concept is primarily based on the unrealistic assumption that the girder plays a role of rigid support against deck deflection. In reality, however, girders are flexible and the deflection of girders affect the behavior of deck slabs. In the present study, an analytical method was developed to take the effect of the girder flexibility on the deck behavior into account. The method was formulated based on the slope-deflection equations of plates and harmonic analysis. Unlike the conventional finite element analysis, the input and output schemes are simple and convenient. The validity of the presented study was verified by a series of comparative studies with finite element analyses and experimental tests. It was shown from the analyses that the negative transverse moments of decks were significantly reduced in many cases when the girder flexibility were appropriately taken into consideration whereas the positive moments tend to increase. This poses a strong need to improve the conventional design concept of decks on rigid girders to those on flexible girders.

Key Words
bridge decks; girder deflection; negative bending moment; harmonic analysis; elastic support.

Address
Department of Civil and Environmental Engineering, Korea University, 5-1 Anam-Dong, Sungbuk-Ku, Seoul, 136-701, South Korea
Korea Railroad Research Institute, 374-1 Woulam-Dong, Ulwang-City, Kyounggi-Do, 437-050, South Korea
Department of Civil and Environmental Engineering, Korea University, 5-1 Anam-Dong, Sungbuk-Ku, Seoul, 136-701, South Korea

Abstract
Many papers which deal with the dynamic instability of shell-like structures under the STEP load have been published. But, there have been few papers related to the dynamic instability of hybrid cable domes. In this study, the dynamic instability of hybrid cable domes considering geometric nonlinearity is investigated by a numerical method. The characteristic structural behaviour of a cable dome shows a strong nonlinearity, so we determine the shape of a cable dome by applying initial stress and examine the indirect buckling mechanism under dynamic external forces. The dynamic critical loads are determined by the numerical integration of the nonlinear equation of motion, and the indirect buckling is examined by using the phase plane to investigate the occurrence of chaos.

Key Words
hybrid structure; cable dome; indirect buckling; nonlinear; initial imperfection; phase plane; chaos.

Address
Department of Architectural Engineering, Semyung University, Jecheon 390-711, Korea
Department of Architectural Engineering, Kyungpook National University, Daegu 702-701, Korea

Abstract
The stochastic optimal nonlinear control of coupled adjacent building structures is studied based on the stochastic dynamical programming principle and the stochastic averaging method. The coupled structures with control devices under random seismic excitation are first condensed to form a reduced-order structural model for the control analysis. The stochastic averaging method is applied to the reduced model to yield stochastic differential equations for structural modal energies as controlled diffusion processes. Then a dynamical programming equation for the energy processes is established based on the stochastic dynamical programming principle, and solved to determine the optimal nonlinear control law. The seismic response mitigation of the coupled structures is achieved through the structural energy control and the dimension of the optimal control problem is reduced. The seismic excitation spectrum is taken into account according to the stochastic dynamical programming principle. Finally, the nonlinear controlled structural response is predicted by using the stochastic averaging method and compared with the uncontrolled structural response to evaluate the control efficacy. Numerical results are given to demonstrate the response mitigation capabilities of the proposed stochastic optimal control method for coupled adjacent building structures.

Key Words
building structure; random vibration; optimal control; stochastic averaging; stochastic dynamical programming.

Address
Department of Mechanics, Zhejiang University, Hangzhou 310027, P. R. China
epartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong

Abstract
The buckling and vibration characteristics of stiffened plates subjected to in-plane concentrated edge loading are studied using finite element method. The problem involves the effects of non-uniform stress distribution over the plate. Buckling loads and vibration frequencies are determined for different plate aspect ratios, boundary edge conditions and load positions. The non-uniform stresses may also be caused due to the supports on the edges. The analysis presented determines the initial stresses all over the region considering the pre-buckling stress state for different kinds of loading and edge conditions. In the structural modeling, the plate and the stiffeners are treated as separate elements where the compatibility between these two types of elements is maintained. The vibration characteristics are discussed and the results are compared with those available in the literature and some interesting new results are obtained.

Key Words
finite element method; stiffened plate; buckling and frequency parameter.

Address
Aerospace Engineering Department, I. I. T. Kharagpur-721302, India
Department of Ocean Engineering and Naval Architecture I. I. T. Kharagpur-721302, India

Abstract
Gradient elastic flexural beams are dynamically analysed by analytic means. The governing equation of flexural beam motion is obtained by combining the Bernoulli-Euler beam theory and the simple gradient elasticity theory due to Aifantis. All possible boundary conditions (classical and non-classical or gradient type) are obtained with the aid of a variational statement. A wave propagation analysis reveals the existence of wave dispersion in gradient elastic beams. Free vibrations of gradient elastic beams are analysed and natural frequencies and modal shapes are obtained. Forced vibrations of these beams are also analysed with the aid of the Laplace transform with respect to time and their response to loads with any time variation is obtained. Numerical examples are presented for both free and forced vibrations of a simply supported and a cantilever beam, respectively, in order to assess the gradient effect on the natural frequencies, modal shapes and beam response.

Key Words
beams; gradient elasticity; flexural vibrations; non-classical boundary conditions; free vibrations; forced vibrations.

Address
General Department, School of Technology, Aristotle University of Thessaloniki, GR-54006 Thessaloniki, Greece
Department of Mechanical and Aeronautical Engineering, University of Patras, GR-26500 Patras, Greece
Department of Civil Engineering, University of Patras, GR-26500 Patras, Greece


Abstract
A time domain method is presented for soil-structure interaction analysis under seismic excitations. It is based on the finite element formulation incorporating infinite elements for the far field soil region. Equivalent earthquake input forces are calculated based on the free field responses along the interface between the near and far field soil regions utilizing the fixed exterior boundary method in the frequency domain. Then, the input forces are transformed into the time domain by using inverse Fourier transform. The dynamic stiffness matrices of the far field soil region formulated using the analytical frequency-dependent infinite elements in the frequency domain can be easily transformed into the corresponding matrices in the time domain. Hence, the response can be analytically computed in the time domain. A recursive procedure is proposed to compute the interaction forces along the interface and the responses of the soil-structure system in the time domain. Earthquake response analyses have been carried out on a multi-layered half-space and a tunnel embedded in a layered half-space with the assumption of the linearity of the near and far field soil region, and results are compared with those obtained by the conventional method in the frequency domain.

Key Words
soil-structure interaction; analytical frequency-dependent infinite element; earthquake response analysis; time domain analysis; recursive procedure.

Address
Department of Civil Engineering, Kunsan National University, San 68, Miryong-Dong, Kunsan, Jeonbuk 573-701, Korea
Department of Civil Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusong-Dong, Yusong-Ku, Daejeon 305-701, Korea

Abstract
The quasi-static and dynamic responses of a linear viscoelastic circular beam on Winkler foundation are studied numerically by using the mixed finite element method in transformed Laplace-Carson space. This element VCR12 has 12 independent variables. The solution is obtained in transformed space and Schapery, Dubner, Durbin and Maximum Degree of Precision (MDOP) transform techniques are employed for numerical inversion. The performance of the method is presented by several quasi-static and dynamic example problems.

Key Words
viscoelastic circular beam; mixed finite element; inverse Laplace transform; elastic foundation.

Address
Faculty of Civil Engineering, Istanbul Technical University, 80626 Maslak-Istanbul, Turkey


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com