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CONTENTS
Volume 27, Number 1, September10 2007
 

Abstract
In the present study, a spline finite strip with higher-order shear deformation is formulated for the stability and free vibration analysis of composite plates. The analysis is conducted based on Reddy?s third-order shear deformation theory, Touratier?s ?Sine? model, Afaq?s exponential model and Cho?s higher-order zigzag laminate theory. Consequently, the shear correction coefficients are not required in the analysis, and an improved accuracy for thick laminates is achieved. The numerical results, based on different shear deformation theories, are resented in comparison with the three-dimensional elasticity solutions. The effects of length-to-thickness ratio, fibre orientation, and boundary conditions on the critical buckling loads and natural frequencies are investigated through numerical examples.

Key Words
stability; free vibration; composite plate; spline finite strip method; Reddy?s third-order shear deformation theory; Touratier?s ?Sine? model; Afaq?s Exponential model; Cho?s higher-order zigzag laminate theory.

Address
G. Akhras and W. Li: Dept. of Civil Engineering, Royal Military College of Canada, P.O. Box 17000, STN Forces, Kingston, Ontario, K7K 7B4, Canada

Abstract
The main source of transverse vibration of a conveyor belt is frictional contact between pulley and belt. Also, environmental characteristics such as natural dampers and springs affect natural frequencies, stability and bifurcation points of system. These phenomena can be modeled by a small velocity fluctuation about mean velocity. Also, viscoelastic foundation can be modeled as the dampers and springs with continuous characteristics. In this study, non-linear vibration of a conveyor belt supported partially by a distributed viscoelastic foundation is investigated. Perturbation method is applied to obtain a closed form analytic solutions. Finally, numerical simulations are presented to show stiffness, damping coefficient, foundation length, non-linearity and mean velocity effects on location of bifurcation points, natural frequencies and stability of solutions.

Key Words
non-linear vibration; stability; perturbation method; viscoelastic foundation.

Address
M. H. Ghayesh and S. E. Khadem: Mechanical & Aerospace Engineering Department, Tarbiat Modarres University, P.O. Box 14115-177, Tehran, Iran

Abstract
An Articulated tower is one of the compliant offshore structures connected to the sea-bed through a universal joint which is the most vulnerable location of the tower that sustains the randomly fluctuating shear stresses. The time history response of the bottom hinge shear is obtained and presented in the spectral form. The fatigue and fracture reliability assessment of the tower joint against randomly varying shear stresses have been carried out. Non-linear limit state functions are derived in terms of important random variables using S-N curve and fracture mechanics approaches. Advanced First Order Reliability Method is used for reliability assessment. Sensitivity analysis shows the influence of various variables on the hinge safety. Fatigue life estimation has been made using probabilistic approach.

Key Words
articulated; off-shore; SPM; random sea; reliability; fatigue; compliant.

Address
Nazrul Islam: Civil Engineering Dept., Jamia Millia Islamia University, New Delhi-110025, India
Suhail Ahmad: Applied Mechanics Dept., Indian Institute of Technology, New Delhi-110016, India

Abstract
This paper presents a modified and improved bi-directional evolutionary structural optimization (BESO) method for topology optimization. A sensitivity filter which has been used in other optimization methods is introduced into BESO so that the design solutions become mesh-independent. To improve the convergence of the optimization process, the sensitivity number considers its historical information. Numerical examples show the effectiveness of the modified BESO method in obtaining convergent and mesh-independent solutions. A study of the effects of various BESO parameters on the solution is then conducted to determine the appropriate values for these parameters.

Key Words
bi-directional evolutionary structural optimization (BESO); numerical stability; mesh-independency; parameters study.ore; SPM; random sea; reliability; fatigue; compliant.

Address
X. Huang and Y. M. Xie: School of Civil and Chemical Engineering, RMIT University, GPO Box 2476V, Melbourne 3001, Australia

Abstract
The code provisions on lap splices are critically assessed in the light of 203 beams without transverse reinforcement and 278 beams with transverse reinforcement. For comparison, the provisions given in the ACI 318, Eurocode 2, and TS 500 Codes are considered. The ACI Committee 408 recommended provision and a new proposal are also taken into account throughout the assessment. The comparison with real beam tests where the splice region was subjected to constant moment indicates that current provisions in the Codes do not agree acceptably with test results. The steel stress prediction graphs calculated by means of the Code provisions show high scatter and remain unsafe especially for test data without transverse reinforcement. Both the recent recommended provision by ACI Committee 408 and a new design expression proposed by the author have much less scatter with fewer unsafe predictions. The simplified design provision proposed by ACI Committee 408 does not yield similar results to that of the advanced design provision proposed by the same committee and therefore it could conveniently be replaced with the simpler equation proposed by the author.

Key Words
lap splice; comparison; code provisions; development length.

Address
Erdem Canbay: Dept. of Civil Engineering, Middle East Technical University, Ankara, 06531, Turkey

Abstract
When assessing buildings that may collapse during a large earthquake, conventional rapid visual screening procedures generally provide good results when identifying buildings for further investigation. Unfortunately, their accuracy at identify buildings at risk is not so good. In addition, there appears to be little room for improvement. This paper investigates an alternative screening procedure based on fuzzy logic and artificial neural networks. Two databases of buildings damaged during the Athens earthquake of 1999 are used for training purposes. Extremely good results are obtained from one database and not so good results are obtained from the second database. This finding illustrates the importance of specifically collecting data tailored to the requirements of the fuzzy logic based rapid visual screening procedure. In general, results demonstrate that the trained fuzzy logic based rapid visual screening procedure represents a marked improvement when identifying buildings at risk. In particular, when smaller percentages of the buildings with high damage scores are extracted for further investigation, the proposed fuzzy screening procedure becomes more efficient. This paper shows that the proposed procedure has a significant optimisation potential, is worth pursuing and, to this end, a strategy that outlines the future development of the fuzzy logic based rapid visual screening procedure is proposed.

Key Words
fuzzy logic; artificial neural networks; rapid visual screening; seismic vulnerability; vulnerability assessment; damage.

Address
V. J. Moseley, S. E. Dritsos and D. L. Kolaksis: Dept. of Civil Engineering, University of Patras, 26500, Patras, Greece

Abstract
In this paper, experimental investigations on the inelastic seismic behavior of tunnel form buildings (i.e., box-type or panel systems) are presented. Two four-story scaled building specimens were tested under quasi-static cyclic lateral loading in longitudinal and transverse directions. The experimental results and supplemental finite element simulations collectively indicate that lightly reinforced structural walls of tunnel form buildings may exhibit brittle flexural failure under seismic action. The global tension/compression couple triggers this failure mechanism by creating pure axial tension in outermost shearwalls. This type of failure takes place due to rupturing of longitudinal reinforcement without crushing of concrete, therefore is of particular interest in emphasizing the mode of failure that is not routinely considered during seismic design of shear-wall dominant structural systems.

Key Words
reinforced concrete; shear-wall; brittle failure; tunnel form building; box system; cyclic loading; finite elements

Address
S. Bahadir Yuksel: Dept. of Civil Engineering, Selcuk University, Konya 42075, Turkey
Erol Kalkan: California Geological Survey, Earthquake Engineering Program, Sacramento, 95814 CA, USA


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