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CONTENTS
Volume 42, Number 3, May10 2012
 

Abstract
The multi-span suspension bridge having double main cables in the vertical plane is investigated regarding endurance of live load distribution in the case of non-displaced pylon and pylon displacement. The coefficient formula of live load distribution described as the ratio of live load on the bottom cable to the top cable is obtained. Based on this formula, some function in respect of this bridge are derived and used to analyze its characteristics. This analysis targets the cable force, the cable sag and the horizontal displacement at the pylon top under live load etc. The results clarified that the performance of the live load distribution and the horizontal force of cables in the case of non-deformed pylon has a similar tendency to those in the case of deformed pylon, and the increase of pylon rigidity can increase live load distributed to the bottom cable and slightly raise the cable horizontal force under live load. However, effect on the vertical rigidity of bridge and the horizontal force increment of cables caused by live load is different in the case of non-deformed pylon and deformed pylon.

Key Words
suspension bridge; double main cables; coefficient of live load distribution; cable sag

Address
Li-wen Zhang, Ru-cheng Xiao, Yang Jiang and Sheng-bo Chai: Department of bridge Engineering, Tongji University, 1239 Siping Rd., Shanghai 200092, China

Abstract
This paper examines the problem of a penny-shaped crack in a thermoporoelastic body. On the basis of the recently developed general solutions for thermoporoelasticity, appropriate potentials are suggested and the governing equations are solved in view of the similarity to those for pure elasticity. Exact and closed form fundamental solutions are expressed in terms of elementary functions. The singularity behavior is then discussed. The present solutions are compared with those in literature and an excellent agreement is achieved. Numerical calculations are performed to show the influence of the material parameters upon the distribution of the thermoporoelastic field. Due to its ideal property, the present solution is a natural benchmark to various numerical codes and simplified analyses.

Key Words
thermoporoelasticity; transversely isotropic; fundamental solution; potential theory method; penny-shaped crack

Address
Xiang-Yu LI: School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu, 610031, P.R. China; UPMC Sisyphe, Boite 105, 4 Place Jussieu, 75252 Paris, Cedex 05, France
J. Wu: Laboratoire d\'Etudes Aerodynamiques, Universite de Poitiers, Bd Marie et Pierre Curie, BP 30179,
Teleport 2, Chasseneuil, Cedex, France
W.Q. Chen: Department of Engineering Mechanics, Zhejiang University, Yuquan Campus, Hangzhou 310027, P.R. China
Hui-Ying Wang: E.N.S.M.A., University of Poitiers, B.P., B.P. 109-Chasseneuil du Poitou 86960 Futuroscope, Cedex, France
Z.Q. Zhou: Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL 33124, USA

Abstract
Particle Swarm Optimization (PSO) is a stochastic population based optimization algorithm which has attracted attentions of many researchers. This method has great potentials to be applied to many optimization problems. Despite its robustness the standard version of PSO has some drawbacks that may reduce its performance in optimization of complex structures such as laminated composites. In this paper by suggesting a new variation scheme for acceleration parameters and inertial weight factors of PSO a novel optimization algorithm is developed to enhance the basic version\'s performance in optimization of laminated composite structures. To verify the performance of the new proposed method, it is applied in two multi-objective design optimization problems of laminated cylindrical. The numerical results from the proposed method are compared with those from two other conventional versions of PSObased algorithms. The convergancy of the new algorithms is also compared with the other two versions. The results reveal that the new modifications inthe basic forms of particle swarm optimization method can increase its convergence speed and evade it from local optima traps. It is shown that the parameter variation scheme as presented in this paper is successful and can evenfind more preferable optimum results in design of laminated composite structures.

Key Words
cylindrical composite laminated shell; optimization algorithms; particle swarm optimization

Address
A. Sepehri: School of Mechanical Engineering, Shiraz University, Shiraz, Iran
F. Daneshmand: School of Mechanical Engineering, Shiraz University, Shiraz, Iran; Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street W.,
Montreal, Quebec, H3A 2K6, Canada
K. Jafarpur: School of Mechanical Engineering, Shiraz University, Shiraz, Iran

Abstract
In this paper decay and mapped elastodynamic infinite elements, based on modified Bessel shape functions and appropriate for Soil-Structure Interaction problems are described and discussed. These elements can be treated as a new form of the recently proposed Elastodynamic Infinite Elements with United Shape Functions (EIEUSF) infinite elements. The formulation of 2D horizontal type infinite elements (HIE) is demonstrated, but by similar techniques 2D vertical (VIE) and 2D corner (CIE) infinite elements can also be formulated. It is demonstrated that the application of the elastodynamical infinite elements is the easier and appropriate way to achieve an adequate simulation including basic aspects of Soil-Structure Interaction. Continuity along the artificial boundary (the line between finite and infinite elements) is discussed as well and the application of the proposed elastodynamical infinite elements in the Finite Element Method is explained in brief. Finally, a numerical example shows the computational efficiency of the proposed infinite elements.

Key Words
soil-structure interaction; wave propagation; infinite elements; finite element method; Bessel functions

Address
K.S. Kazakov: Department of Structural Mechanics, VSU, Sofia, Bulgaria

Abstract
This study is aimed at providing an efficient analytical model to obtain pressure- impulse diagram of one-way reinforced concrete slabs subjected to different shapes of air blast loading using single degree of freedom method (SDOF). A tri-linear elastic perfectly plastic SDOF model has been used to obtain the pressure-impulse diagram to correlate the blast pressure and the corresponding concrete flexural damage. In order to capture the response history for the slab, a new approximately SDOF method based on the conventional SDOF method is proposed and validated using published test data. The influences of pulse loading shape on the pressure-impulse diagram are studied. Based on the results, a pressure-impulse diagram generation method using SDOF and an analytical equation for the pressureimpulse diagram is proposed to different damage levels and different blast loading shapes.

Key Words
blast load; SDOF; pressure-impulse diagram; one-way concrete slab

Address
Wei Wang, Duo Zhang and Fangyun Lu: Institute of Technique Physics, College of Science, National University of Defense Technology, Changsha, Hunan, 410073, P.R. China

Abstract
A numerical approach to simulate the behaviour of timber shear walls under both static and dynamic loading is proposed. Because the behaviour of timber shear walls hinges on the behaviour of the nail connections, the force-displacement behaviour of sheathing-to-framing nail connections are first determined and then used to define the hysteretic properties of finite elements representing these connections. The model nails are subsequently implemented into model walls. The model walls are verified using experimental results for both monotonic and cyclic loading. It is demonstrated that the complex hysteretic behaviour of timber shear walls can be reasonably represented using model shear walls in which nonlinear material failure is concentrated only at the sheathing-to-framing nail connections.

Key Words
timber shear walls; midply; numerical simulation; hysteresis; nail connections; cyclic; monotonic

Address
Wei Yuen Loo, Pierre Quenneville and Nawawi Chouw: Department of Civil and Environmental Engineering, School of Engineering, University of Auckland, New Zealand

Abstract
Since relatively low elasticity modulus of the FRP materials results in lower natural frequencies, it is necessary to study the free vibration of FRP transmission poles. In this paper, the free vibration of tapered FRP transmission poles with thin-walled circular cross-section is investigated by a tapered beam element. To model the flexible joints of the modular poles, a rotational spring model is used. Modal analysis is performed for typical FRP poles with/without joint and they are also modeled by ANSYS commercial finite element software. There is a good correlation between the results of the tapered beam finite element model and those obtained from ANSYS as well as the existing experimental results. The effects of different geometries, material lay-ups, concentrated masses at the pole tip, and joint flexibilities are evaluated. Moreover, it is concluded that using tougher fibres at the inner and outer layers of the cross-section, results in higher natural frequencies, significantly.

Key Words
transmission pole; fiber-reinforced polymer; flexible joint; free vibration; finite element method

Address
Behnam Saboori: Centre of Excellence for Research in Advanced Materials & Structures, Faculty of Mechanical
Engineering, K.N. Toosi University of Technology, Pardis St., Molasadra Ave., Vanak Sq., Tehran, Iran
Seyed Mohammad Reza Khalili: Centre of Excellence for Research in Advanced Materials & Structures, Faculty of Mechanical Engineering, K.N. Toosi University of Technology, Pardis St., Molasadra Ave., Vanak Sq., Tehran, Iran; Faculty of Engineering, Kingston University, London, UK

Abstract
In this paper, a new damage detection and quantification method has been presented to perform detection and quantification of structural damage under ambient vibration loadings. To extract modal properties of the structural system under ambient excitation, natural excitation technique (NExT) and eigensystem realization algorithm (ERA) are employed. Sensitivity matrices of the dynamic residual force vector have been derived and used in the parameter subset selection method to identify multiple damaged locations. In the sequel, the steady state genetic algorithm (SSGA) is used to determine quantified levels of the identified damage by minimizing errors in the modal flexibility matrix. In this study, performance of the proposed damage detection and quantification methodology is evaluated using a finite element model of a truss structure with considerations of possible experimental errors and noises. A series of numerical examples with five different damage scenarios including a challengingly small damage level demonstrates that the proposed methodology can efficaciously detect and quantify damage under noisy ambient vibrations.

Key Words
modal identification; Eigensystem Realization Algorithm (ERA); Natural Excitation Technique (NExT); subset selection; genetic algorithm; damage detection; structural health monitoring

Address
Gun Jin Yun: Department of Civil Engineering, The University of Akron, Akron, OH, 44325-3905, USA


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