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CONTENTS
Volume 28, Number 1, January10 2008
 

Abstract
The conventional design of bridge piers against scour uses scour equations which involve number of uncertain flow, sediments and structural parameters. The inherent high uncertainties in these parameters suggest that the reliability of piers must be assessed to ensure desirable safety of bridges against scour. In the present study, a procedure for the reliability assessment of bridge piers, installed in main and flood channels, against scour has been presented. To study the influence of various random variables on piers? reliability sensitivity analysis has been carried out. To incorporate the reliability in the evaluation of safety factor, a simplified relationship between safety factor and reliability index has been proposed. Effects of clear water (flood channel) and live bed scour (main channel) are highlighted on pier reliability. In addition to these, an attempt has also been made to explain the failure of Black mount bridge of New Zealand based on its pier?s reliability analysis. Some parametric studies have also been included to obtain the results of practical interest.

Key Words
piers; scouring; bridges; reliability; FORM; Monte Carlo Simulation.

Address
Department of Civil Engineering, Aligarh Muslim University, Aligarh, 202 002, India

Abstract
A general solution to the field equations of homogeneous isotropic generalized thermoelastic diffusion with two relaxation times (Green and Lindsay theory) has been obtained using the Fourier
transform. Assuming the disturbances to be harmonically time.dependent, the transformed solution is obtained in the frequency domain. The application of a time harmonic concentrated and distributed loads
have been considered to show the utility of the solution obtained. The transformed components of displacement, stress, temperature distribution and chemical potential distribution are inverted numerically, using a numerical inversion technique. Effect of diffusion on the resulting expressions have been depicted graphically for Green and Lindsay (G-L) and coupled (C-T) theories of thermoelasticity.

Key Words
generalized thermoelastic diffusion; time harmonic; concentrated and distributed loads; fourier transform.

Address
Nidhi Sharma: Dept. of Mathematics, N I T, Kurukshetra-136119, India
Rajneesh Kumar: Dept. of Mathematics, Kurukshetra University, Kurukshetra, India
Paras Ram: Dept. of Mathematics, N I T, Kurukshetra-136119, India

Abstract
Column shear failures observed during recent earthquakes and experimental data indicate that shear deformations are typically associated with the amount of transverse reinforcement, column aspect ratio, axial load, and a few other parameters. It was shown that in some columns shear displacements can be significantly large, especially after flexural yielding. In this paper, a piecewise linear model is
developed to predict an envelope of the cyclic shear response including the shear displacement and corresponding strength predictions at the first shear cracking, peak strength, onset of lateral strength
degradation, and loss of axial-load-carrying capacity. Part of the proposed model is developed using the analysis results from the Modified Compression Field Theory (MCFT). The results from the proposed model, which uses simplified equations, are compared with the column test data.

Key Words
shear deformation; reinforced concrete column; seismic response; shear failure; shear strength degradation.

Address
Halil Sezen: Dept. of Civil and Environment Engineering and Geodetic Science, The Ohio State University, 470 Hitchcock Hall, 2070 Neil Avenue, Columbus, OH 43210, USA

Abstract
Anisotropic materials are increasingly required in modern technological applications. Certainly, civil, mechanical and naval engineers frequently deal with the situation of analyzing the dynamical behaviour of structural elements being composed of such materials. For example, panels of anisotropic materials must sometimes support electromechanical engines, and besides, holes are performed in them for operational reasons e.g., conduits, ducts or electrical connections. This study is concerned with the natural frequencies and normal modes of vibration of rectangular anisotropic plates supported by different combinations of the classical boundary conditions: clamped, simply . supported and free, and with additional complexities such holes of free boundaries and attached concentrated masses. A variational
approach (the well known Ritz method) is used, where the displacement amplitude is approximated by a set of beam functions in each coordinate direction corresponding to the sides of the rectangular plate.
Consequently each coordinate function satisfies the essential boundary conditions at the outer edge of the plate. The influence of the position and magnitude of both hole and mass, on the natural frequencies and modal shapes of vibration are studied for a generic anisotropic material. The classical Ritz method with beam functions as spatial approximation proved to be a suitable procedure to solve a problem of such
analytical complexity.

Key Words
vibration of plates; anisotropic plates; concentrated mass; holes of free edge; Ritz method.

Address
C. A. Rossit: Dpto. de Ingenieria, Instituto de Mecanica Aplicada, Universidad Nacional del Sur, 8000, Bahia Blanca, Argentina
P. M. Ciancio: Facultad de Ingenieria, Universidad Nacional del Centro de la Provincia de Buenos Aires, 7400, Olavarria, Argentina

Abstract
A number of construction practices, implemented during the design process of a reinforced concrete (RC) structural system, may have significant consequences on the behaviour of the structural system
in the case of earthquake loading. Although a number of provisions are imposed by the contemporary Greek national design codes for the seismic design of RC structures, in order to reduce the consequences, the influence of the construction practices on the seismic behaviour of the structural system remains significant. The objective of this work is to perform a comparative study in order to examine the influence of three, often encountered, construction practices namely weak ground storey, short and floating columns and two combinations on the seismic performance of the structural system with respect to the structural capacity and the maximum interstorey drifts in three earthquake hazard levels.

Key Words
construction practice; Greek national design codes; capacity spectrum method; hazard levels.

Address
Nikos D. Lagaros: Institute of Structural Analysis & Seismic Research, National Technical University of Athens, 9, Iroon Polytechniou Str., Zografou Campus, 157 80 Athens, Greece
Dept. of Civil Engineering, University of Thessaly, Pedion Areos, 383 34 Volos, Greece
Martha A. Geraki: Dept. of Civil Engineering, University of Thessaly, Pedion Areos, 383 34 Volos, Greece

Abstract
The paper presents a study on the effects of soil-structure-interaction (SSI) on the performance of the compliant liquid column damper (CLCD) for the seismic vibration control of short period structures. The frequency-domain formulation for the input-output relation of a flexible-base structure with CLCD has been derived. The superstructure has been modeled as a linear, single degreeof- freedom (SDOF) system. The foundation has been considered to be attached to the underlying soil medium through linear springs and viscous dashpots, the properties of which have been represented by complex valued impedance functions. By using a standard equivalent linearization technique, the nonlinear orifice damping of the CLCD has been replaced by equivalent linear viscous damping. A
numerical stochastic study has been carried out to study the functioning of the CLCD for varying degrees of SSI. Comparison of the damper performance when it is tuned to the fixed-base structural frequency and when tuned to the flexible-base structural frequency has been made. The effects of SSI on the optimal value of the orifice damping coefficient of the damper has also been studied. A more convenient approach for designing the damper while considering SSI, by using an established model of a replacement oscillator for the structure-soil system has also been presented. Finally, a simulation study, using a recorded accelerogram, has been carried out on the CLCD performance for the flexible-base structure.

Key Words
CLCD; SSI; complex valued impedance functions; short period structures; seismic vibration; equivalent SDOF oscillator; time history analysis.

Address
Ratan Kumar Ghosh and Aparna (Dey) Ghosh: Dept. of Civil Engineering, Bengal Engineering & Science University, Shibpur, Howrah, India

Abstract
Wind turbine blades are increasing in magnitude without a proportional increase of stiffness for which reason geometrical and inertial nonlinearities become increasingly important. Often these effects
are analysed using a nonlinear truncated expansion in undamped fixed base mode shapes of a blade, modelling geometrical and inertial nonlinear couplings in the fundamental flap and edge direction. The purpose of this article is to examine the applicability of such a reduced-degree-of-freedom model in predicting the nonlinear response and stability of a blade by comparison to a full model based on a nonlinear co-rotating FE formulation. By use of the reduced-degree-of-freedom model it is shown that under strong resonance excitation of the fundamental flap or edge modes, significant energy is transferred to higher modes due to parametric or nonlinear coupling terms, which influence the response and stability conditions. It is demonstrated that the response predicted by such models in some cases becomes instable or chaotic. However, as a consequence of the energy flow the stability is increased and the tendency of chaotic vibrations is reduced as the number of modes are increased. The FE model representing the case of infinitely many included modes, is shown to predict stable and ordered response for all considered parameters. Further, the analysis shows that the reduced-degree-of-freedom model of relatively low order overestimates the response near resonance peaks, which is a consequence of the small number of included modes. The qualitative erratic response and stability prediction of the reduced order models take place at frequencies slightly above normal operation. However, for normal operation of the wind turbine without resonance excitation 4 modes in the reduced-degree-of-freedom model perform acceptable.

Key Words
wind turbine blades; nonlinear vibration; bernoulli-euler beam; co-rotating finite elements; truncated modal expansion.

Address
K. Holm-J?rgensen, J.W. St?rdahl and S.R.K. Nielsen:
Dept. of Civil Engineering, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark


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