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CONTENTS
Volume 28, Number 4, March10 2008
 

Abstract
This study investigates effect of uncertainty in natural vibration period on the seismic demand. It is shown that since this uncertainty affects the acceleration and displacement responses differently, two ratios, one relating peak acceleration responses and the other relating the peak displacement responses, are not equal and both must be employed in evaluating and defining the critical seismic demand. The evaluation of the ratios is carried out using more than 200 strong ground motion records. The results suggest that the uncertainty in the natural vibration period impacts significantly the statistics of the ratios relating the peak responses. By using the statistics of the ratios, a procedure and sets of empirical equations are developed for estimating the probability consistent seismic demand for both linear and nonlinear systems.

Key Words
peak linear elastic responses; peak inelastic responses; probability; seismic demand;uncertainty.

Address
H.P. Hong and S.S. Wang: Dept. of Civil and Environmental Engineering, University of Western Ontario, Canada
A.K.H. Kwan: Dept. of Civil Engineering, University of Hong Kong

Abstract
In this study stochastic analysis of non-linear dynamical systems under ?-stable, multiplicative white noise has been conducted. The analysis has dealt with a special class of ?-stable stochastic processes namely sub-Gaussian white noises. In this setting the governing equation either of the probability density function or of the characteristic function of the dynamical response may be obtained
considering the dynamical system forced by a Gaussian white noise with an uncertain factor with ?/2-stable distribution. This consideration yields the probability density function or the characteristic function of the response by means of a simple integral involving the probability density function of the system under Gaussian white noise and the probability density function of the ?/2-stable random parameter. Some numerical applications have been reported assessing the reliability of the proposed formulation. Moreover a proper way to perform digital simulation of the sub-Gaussian ?-stable random process preventing dynamical systems from numerical overflows has been reported and discussed in detail.

Key Words
Levy white noise; stochastic differential calculus; Fokker-Planck equation; sub-Gaussian white noise.

Address
Mario Di Paola, Antonina Pirrotta and Massimiliano Zingales: Dipartimento di Ingegneria Strutturale e Geotecnica, Palermo, Viale delle Scienze, I-90128, Italy

Abstract
The fatigue damage accumulation rates of horizontally curved thin walled box-girder bridge have been estimated from vehicle-induced dynamic stress history using rain flow cycle counting method in the time domain approach. The curved box-girder bridge has been numerically modeled using computationally efficient thin walled box-beam finite elements, which take into account the important structural actions like torsional warping, distortion and distortional warping in addition to the conventional displacement and rotational degrees of freedom. Vehicle model includes heave-pitch-roll degrees of freedom with longitudinal and transverse input to the wheels. The bridge deck unevenness, which is taken as inputs to the vehicle wheels, has been assumed to be a realization of homogeneous random process specified by a power spectral density (PSD) function. The linear damage accumulation theory has been applied to calculate fatigue life. The fatigue life estimated by cycle counting method in time domain has been compared with those found by estimating the PSD of response in frequency domain. The frequency domain method uses an analytical expression involving spectral moment characteristics of stress process.
The effects of some of the important parameters on fatigue life of the curved box bridge have been studied.

Key Words
fatigue life; horizontally curved; thin walled box-girder; finite elements; cycle counting; linear damage accumulation; power spectral density.

Address
K. Nallasivam, Sudip Talukdar and Anjan Dutta: Dept. of Civil Engineering, Indian Institute of Technology Guwahati-781039, India

Abstract
Ground motions in near source region of large crustal earthquakes are significantly affected by rupture directivity and tectonic fling. These effects are the strongest at longer periods and they can have a significant impact on Engineering Structures. In this paper, it is aimed to determine near-fault ground motion effects on the nonlinear response of dams including dam-reservoir-foundation interaction.
Four different types of dam, which are gravity, arch, concrete faced rockfill and clay core rockfill dams, are selected to investigate the near-fault ground motion effects on dam responses. The behavior of
reservoir is taken into account by using Lagrangian approach. Strong ground motion records of Duzce (1999), Northridge (1994) and Erzincan (1992) earthquakes are selected for the analyses. Displacements, maximum and minimum principal stresses are determined by using the finite element method. The displacements and principal stresses obtained from the four different dam types subjected to these nearfault strong-ground motions are compared with each other. It is seen from the results that near-fault ground motions have different impacts on the dam types.

Key Words
arch dam; clay core rockfill dam; concrete faced rockfill dam; concrete gravity dam; dam-reservoir-foundation interaction; finite element method; near-fault strong ground motion.

Address
Alemdar Bayraktar, Ahmet Can Altunisik and Baris Sevim: Dept. of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
Murat Emre Kartal: Dept. of Civil Engineering, Zonguldak Karaelmas University, 67100, Zonguldak, Turkey
Temel Turker: Dept. of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey

Abstract
The aim of this paper is to propose a design procedure for predicting the buckling strength of built-up, cold-formed steel columns based on the two well known methods; the effective width method and the Direct Strength Method. Several design approaches, based on different elastic buckling solutions, were considered in this investigation. Traditional hand methods, without interaction effects between the different modes, and a new numerical spline finite strip method were used to predict the buckling stresses. All of the proposed methods were compared with experimental data on plain and lipped, built-up columns. Results have shown that the effective width approaches are more accurate than the Direct Strength Method. However, both methods can be investigated using more experimental data to assess a
practical design method for built-up columns.

Key Words
buckling; built-up columns; DSM; effective width; spline finite strip.

Address
A. Megnounif and M. Djafour: Dept. of Civil Engineering, A. Belkaid University of Tlemcen, B.P. 230, Tlemcen, Algeria
A. Belarbi: Dept. of Civil, Architectural, and Environmental Engineering, Missouri University of
Science and Technology, Rolla, Missouri, USA
D. Kerdal: Dept. of Civil Engineering, University of Sciences and Technology of Oran, Oran, Algeria

Abstract
An adaptive finite element method for analyzing two-dimensional and axisymmetric nonlinear elastic fracture mechanics problems with cracks is presented. The J-integral is used as a parameter to characterize the severity of stresses and deformation near crack tips. The domain integral technique, for which all relevant quantities are integrated over any arbitrary element areas around the crack tips, is utilized as the J-integral solution scheme with 9-node degenerated crack tip elements. The solution accuracy is further improved by incorporating an error estimation procedure onto a remeshing algorithm
with a solution mapping scheme to resume the analysis at a particular load level after the adaptive remeshing technique has been applied. Several benchmark problems are analyzed to evaluate the
efficiency of the combined domain integral technique and the adaptive finite element method.

Key Words
adaptive finite element method; domain integral technique; J-integral; solution mapping.

Address
Sutthisak Phongthanapanich: Mechanical Engineering Technology Department, College of Industrial Technology, King Mongkut?s University of Technology North Bangkok, Bangkok 10800, Thailand
Kobsak Potjananapasiri and Pramote Dechaumphai:
Mechanical Engineering Department, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand

Abstract
In this study an approximate method based on the continuum approach and transfer matrix method for static and dynamic analyses of stiffened multi-bay coupled shear walls is presented. In this method the whole structure is idealized as a sandwich beam. Initially the differential equation of this equivalent sandwich beam is written then shape functions for each storey is obtained by the solution of differential equations. By using boundary conditions and storey transfer matrices which are obtained by these shape functions, system modes and periods can be calculated. Reliability of the study is shown with a few examples. A computer program has been developed in MATLAB and numerical samples have been solved for demonstration of the reliability of this method. The results of the samples show the agreement between the present method and the other methods given in literature.

Key Words
stiffened coupled shear wall; transfer matrix; static; dynamic.

Address
Kanat Burak Bozdogan and Duygu Ozturk: Civil Engineering Department, Ege University, Izmir, Turkey

Abstract
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Key Words
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Address
Jia-Jang Wu: Dept. of Marine Engineering, National Kaohsiung Marine University, No. 142, Hai-Chuan Road, Nan-Tzu, Kaohsiung 811, Taiwan, Republic of China


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