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CONTENTS
Volume 45, Number 2, January25 2013
 

Abstract
Based on link-model, we conducted a static analysis and computation of a three-span suspended cable structure in the present paper, and obtained the static configuration and tension distribution of the cable. Using the link and beam model based on finite element method, we analyzed the vibration modal of three-span suspended cable structure, and compared with the results obtained from ANSYS using link and beam element. The vibration modals of shallow sagging inclined cables calculated from proposed method agrees well with ANSYS results, which validates the proposed method. As a result, the influence of bend stiffness on in-plane natural frequencies is much greater than that on out-of-plane natural frequencies of inclined cables.

Key Words
inclined cables; link-model; beam-model; static analysis; non-linear vibration

Address
Zhi-Jiang Li: Central South University, Changsha 430011, China
Peng Li: China ship development and design center, Wuhan 430064, China
Zeng He: Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment, Wuhan 430074, China
Ping Cao: Central South University, Changsha 430011, China

Abstract
The effect of structural uncertainties or measurement errors on damage detection results makes the robustness become one of the most important features during identification. Due to the wide use of vibration signatures on damage detection, the development of vibration-based techniques has attracted a great interest. In this work, a review on vibration-based robust detection techniques is presented, in which the robustness is considerably improved through modeling error compensation, environmental variation reduction, denoising, or proper sensing system design. It is hoped that this study can give help on structural health monitoring or damage mitigation control.

Key Words
robust damage detection; modeling error; environmental variation; denoising; sensing system design; vibration signatures

Address
Y.Y. Li: Department of Mechanical and Automation Engineering, The Chinese University of Hong Kong, Sha Tin, New Territories, Hong Kong
Y. Chen: School of Mechatronics Engineering, University of Electronic Science and Technology of China, Chengdu, China

Abstract
The mechanical behavior of rectangular foundation plates with perimetric beams and internal stiffening beams of the plate is herein analyzed, taking the foundation design into account. A series of dimensionless parameters related to the geometry of the studied elements were defined. In order to generalize the problem statement, an initial settlements was considered. A numeric procedure was developed for the resolution by means of the Finite Differences Method that takes into account the stiffness of the plate, the perimetric and internal plate beams and the soil reaction module. Iterative algorithms were employed which, for each of the analyzed cases, made it possible to find displacements and reaction percentages taken by the plate and those that discharge directly into the perimetric beams, practically without affecting the plate. To enhance its mechanical behavior the internal stiffening beams were prestressed and the results obtained with and without prestressing were compared. This analysis was made considering the load conditions and the soil reaction module constant.

Key Words
elastic foundation; plates, prestressed beam; Finite Differences Method; finite elements method

Address
C.J. Orbanich and N.F. Ortega: Department of Engineering, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca, Argentina

Abstract
Current methods of analysis of trusses depend on matrix formulations based on equilibrium equations which are in fact derived from energy principles, and compatibility conditions. Recently it has been shown that the minimum energy principle, by itself, in its pure and unmodified form, can well be exploited to analyze structures when coupled with an optimization algorithm, specifically with a meta-heuristic algorithm. The resulting technique that can be called Total Potential Optimization using Meta-heuristic Algorithms (TPO/MA) has already been applied to analyses of linear and nonlinear plane trusses successfully as coupled with simulated annealing and local search algorithms. In this study the technique is applied to both 2-dimensional and 3-dimensional trusses emphasizing robustness, reliability and accuracy. The trials have shown that the technique is robust in two senses: all runs result in answers, and all answers are acceptable as to the reliability and accuracy within the prescribed limits. It has also been shown that Harmony Search presents itself as an appropriate algorithm for the purpose.

Key Words
meta-heuristics; harmony search; total potential optimization method; truss; nonlinearity; robustness

Address
Yusuf Cengiz Toklu: Department of Civil Engineering, Faculty of Engineering, Bayburt University, 69000 Bayburt, Turkey
Gebrail Bekdas and Rasim Temur: Department of Civil Engineering, Faculty of Engineering, Istanbul University, 34320 Avcilir, Istanbul, Turkey

Abstract
A new dynamic reliability analysis of structure under repeated random loads is proposed in this paper. The proposed method is developed based on the idea that the probability density of several times random loads can be derived from the probability density of single-time random load. The reliability prediction models of structure based on time responses under several times random loads with and without strength degradation are obtained by using the stress-strength interference theory and probability density evolution method. The resulting differential equations in the prediction models can be solved by using the forward finite difference method. Then, the probability density functions of strength redundancy of the structures can be obtained. Finally, the structural dynamic reliability can be calculated using integral method. The efficiency of the proposed method is demonstrated numerically through a speed reducer. The results have shown that the proposed method is practicable, feasible and gives reasonably accurate prediction.

Key Words
probability density evolution; random loads; structure; dynamic; reliability

Address
Yongfeng Fang, Jianjun Chen: Key Laboratory of Electronic Equipment Structure Design, Ministry of Education,
Xidian University, Xi\'an 710071, China
Kong Fah Tee: 2Department of Civil Engineering, University of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB, United Kingdom

Abstract
In this study a multi-objective optimization problem is solved. The objectives used here include simultaneous minimum construction cost in term of sections weight, minimum structural damage using a damage index, and minimum non-structural damage in term of inter-story drift under the applied ground motions. A high-speed and low-error neural network is trained and employed in the process of optimization to estimate the results of non-linear time history analysis. This approach can be utilized for all steel or concrete frame structures. In this study, the optimal design of a planar eccentric braced steel frame is performed with great detail, using the presented multi-objective algorithm with a discrete population and then a moment resisting frame is solved as a supplementary example.

Key Words
seismic design; multi-objective optimization; eccentric braced frame (EBF); moment resisting frame; neural networks; damage index; construction cost

Address
A. Kaveh: Centre of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Tehran-16, Iran
I. Shojaei: School of Civil Engineering, College of Engineering, University of Tehran, Iran; Engineering Optimization Research Group, College of Engineering, University of Tehran, Iran
Y. Gholipour: Engineering Optimization Research Group, College of Engineering, University of Tehran, Iran
H. Rahami: Engineering Optimization Research Group, College of Engineering, University of Tehran, Iran; School of Engineering Science, College of Engineering, University of Tehran, Iran

Abstract
Given the yield shear of a single-story inelastic structure with simple eccentricity, the problem of strength distribution among the resisting elements is investigated, with respect to minimize its torsional response during a ground motion. Making the hypothesis that the peak accelerations, of both modes of vibration, are determined from the inelastic acceleration spectrum, and assuming further that a peak response quantity is obtained by an appropriate combination rule (square root of sum of squares-SRSS or complete quadratic combination-CQC), the first aim of this study is to present an interaction relationship between the yield shear and the maximum torque that may be developed in such systems. It is shown that this torque may be developed, with equal probability, in both directions (clockwise and anticlockwise), but as it is not concurrent with the yield shear, a rational design should be based on a combination of the yield shear with a fraction of the peak torque. The second aim is to examine the response of such model structures under characteristic ground motions. These models provide a rather small peak rotation and code provisions that are based on such principles (NBCC-1995, UBC-1994, EAK-2000, NZS-1992) are superiors to EC8 (1993) and to systems with a stiffness proportional strength distribution.

Key Words
eccentric structures; modal analysis; inelastic spectra

Address
George K. Georgoussis: Department of Civil and Construction Engineering, School of Pedagogical and Technological Education
(ASPETE), N. Heraklion 14121, Attica, Greece

Abstract
Free vibration of symmetric angle-ply layered conical shell frusta of variable thickness is analyzed under shear deformation theory with different boundary conditions by applying collocation with spline approximation. Linear and exponential variation in thickness of layers are assumed in axial direction. Displacements and rotational functions are approximated by Bickley-type splines of order three and obtained a generalized eigenvalue problem. This problem is solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The vibration of three and five–layered conical shells, made up of two different type of materials are considered. Parametric studies are made for analysing the frequencies of the shell with respect to the coefficients of thickness variations, length-to-radius ratio, length-to-thickness ratio and ply angles with different combination of the materials. The results are compared with the available data and new results are presented in terms of tables and graphs.

Key Words
free vibration; conical shells; shear deformation; spline; angle-ply1

Address
K.K.Viswanathan, Saira Javed and Zainal Abdul Aziz: Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Johor, Malaysia

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