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CONTENTS
Volume 51, Number 6, September25 2014
 

Abstract
Meshless local collocation method produces much better conditioned matrices than meshless global collocation methods. In this paper, the meshless local collocation method based on thin plate spline radial basis function and first-order shear deformation theory are used to calculate the natural frequencies and mode shapes of laminated composite shells. Through numerical experiments, the accuracy and efficiency of present method are demonstrated.

Key Words
meshless local collocation; thin plate spline; radial basis function; natural frequencies; mode shapes; laminated composite shell

Address
Song Xiang : Liaoning Key Laboratory of General Aviation, Shenyang Aerospace University, No. 37 Daoyi South Avenue, Shenyang, Liaoning, 110136, People\'s Republic of China
Ying-tao Chen : Faculty of Aerospace engineering, Shenyang Aerospace University, No. 37 Daoyi South Avenue, Shenyang, Liaoning, 110136, People\'s Republic of China

Abstract
In this paper, we present an alternative seismic design strategy for cable stayed bridges with concrete pylons when subjected to strong ground motions. The comparison of conventional seismic design using supplemental dampers (strategy A) and the new strategy using nonlinear seismic design of pylon columns (strategy B) is exemplified by one typical medium span cable stayed bridge subjected to strong ground motions from 1999 Taiwan Chi-Chi earthquake and 2008 China Wenchuan earthquake. We first conducted the optimization of damper parameters according to strategy A in response to the distinct features that strong ground motions contain. And then we adopted strategy B to carry out seismic analysis by introducing the elastic-plastic elements that allowing plasticity development in the pylon columns. The numerical results show that via strategy A, the earthquake induced structural responses can be kept in the desired range provided with the proper damping parameters, however, the extra cost of unusual dampers will be inevitable. For strategy B, the pylon columns may not remain elastic and certain plasticity developed, but the seismic responses of the foundation will be greatly decreased, meanwhile, the displacement at the top of pylon seems to be not affected much by the yielding of pylon columns, which indicates the pylon nonlinear design can be an alternative design strategy when strong ground motions have to be considered for the bridge.

Key Words
seismic design; cable stayed bridge; strong ground motion; concrete pylon; nonlinear seismic behavior

Address
Yan Xu, Jianzhong Li : State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Xinzhi Duan : Shanghai Municipal Engineering Design and Research Institute, 200092, China

Abstract
The rational finite element method is different from the standard finite element method, which is constructed using basic solutions of the governing differential equations as interpolation functions in the elements. Therefore, it is superior to the isoparametric approach because of its obvious physical meaning and accuracy; it has successfully been applied to the isotropic elasticity problem. In this paper, the formulation of rational finite elements for plane orthotropic elasticity problems is deduced. This method is formulated directly in the physical domain with full consideration of the requirements of the patch test. Based on the number of element nodes and the interpolation functions, different approaches are applied with complete polynomial interpolation functions. Then, two special stiffness matrixes of elements with four and five nodes are deduced as a representative application. In addition, some typical numerical examples are considered to evaluate the performance of the elements. The numerical results demonstrate that the present method has a high level of accuracy and is an effective technique for solving plane orthotropic elasticity problems.

Key Words
orthotropic; elastic problem; rational finite element method

Address
Ling Mao, Weian Yao, Qiang Gao and Wanxie Zhong : State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian, 116024, P.R. China

Abstract
Using the infinitesimal theory of elasticity and analytical formulation based on the first-order shear deformation theory (FSDT) is presented for axisymmetric thick-walled cylinders made of functionally graded materials under internal and/or external uniform pressure. The material is assumed to be isotropic heterogeneous with constant Poisson\'s ratio and radially exponentially varying elastic modulus. At first, general governing equations of the FGM thick cylinders are derived by assumptions of the FSDT. Then the obtained equations are solved under the generalized clamped-clamped conditions. The results are compared with the findings of both FSDT and finite element method (FEM).

Key Words
thick cylinders; shear deformation theory; exponential; FGM; FSDT; FEM

Address
Mehdi Ghannad and Hamed Gharooni : Department of Mechanical Engineering, Shahrood University of Technology, Shahrood, Iran

Abstract
Large post-buckling behavior of Timoshenko beams subjected to non-follower axial compression loads are studied in this paper by using the total Lagrangian Timoshenko beam element approximation. Two types of support conditions for the beams are considered. In the case of beams subjected to compression loads, load rise causes compressible forces end therefore buckling and postbuckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The beams considered in numerical examples are made of lower-Carbon Steel. In the study, the relationships between deflections, rotational angles, critical buckling loads, post-buckling configuration, Cauchy stress of the beams and load rising are illustrated in detail in post-buckling case.

Key Words
gometrical non-linearity; post-buckling analysis; total Lagrangian finite element model; timoshenko beam; large displacements; large rotations

Address
Şeref D. Akbaş : Department of Civil Engineering, Bursa Technical University, Yildirim Campus, 152 Evler Mah., Egitim Cad., 1. Damla Sok., No:2/10, 16330 Yildirim, Bursa, Turkey

Abstract
This paper presents a factor-analysis based questionnaire categorization method to improve the reliability of the evaluation of working conditions without influencing the completeness of the questionnaire both in Taiwanese and Chinese construction enterprises for structural engineering applications. The proposed approach springs from the AI application and expert systems in structural engineering. Questions with a similar response pattern are grouped into or categorized as one factor. Questions that form a single factor usually have higher reliability than the entire questionnaire, especially in the case when the questionnaire is complex and inconsistent. By classifying questions based on the meanings of the words used in them and the responded scores, reliability could be increased. The principle for classification was that 90% of the questions in the same classified group must satisfy the proposed classification rule and consequently the lowest one was 92%. The results show that the question classification method could improve the reliability of the questionnaires for at least 0.7. Compared to the question deletion method using SPSS, 75% of the questions left were verified the same as the results obtained by applying the classification method.

Key Words
construction enterprise; expert system; factor analysis; questionnaire categorization; reliability improvement; working condition

Address
Jeng-Wen Lin : Department of Civil Engineering, Feng Chia University, Taichung 40724, Taiwan, R.O.C
Pu Fun Shen : Ph.D. Program in Civil and Hydraulic Engineering, Feng Chia University, Taichung 40724, Taiwan, R.O.C

Abstract
In the preliminary design stage of an RC 3D-frame, repeated sequential analyses to determine optimal members\' sizes and the investigation of the parameters required to minimize the differential column shortening are computational effort consuming, especially when considering various types of loads such as dead load, temperature action, time dependent effects, construction and live loads. Because the desired accuracy at this stage does not justify such luxury, two backpropagation feedforward artificial neural networks have been proposed in order to approximate this information. Instead of using a commercial software package, many references providing advanced principles have been considered to code a program and generate these neural networks. The first one predicts the typical amount of time between two phases, needed to achieve the minimum maximorum differential column shortening. The other network aims to prognosticate sequential analysis results from those of the simultaneous analysis. After the training stages, testing procedures have been carried out in order to ensure the generalization ability of these respective systems. Numerical cases are studied in order to find out how good these ANN match with the sequential finite element analysis. Comparison reveals an acceptable fit, enabling these systems to be safely used in the preliminary design stage.

Key Words
sequential analysis; differential column shortening; optimization; minimization; finite element analysis; 3D-frame; artificial neural network

Address
Wilfried W. Njomo : Department of Civil Engineering, Middle East Technical University, Ankara, Turkey
Giray Ozay : Department of Civil Engineering, Eastern Mediterranean University, Famagusta, via Mersin 10, Turkey

Abstract
Roles of reactor internals are to support nuclear fuel, provide insertion and withdrawal channels of nuclear fuel control rods, and carry out core cooling. In case of functional loss of the reactor internals, it may lead to severe accidents caused by damage of nuclear fuel assembly and deterioration of reactor vessel due to attack of fallen out parts. The present study is to examine fluid flows in reactor internals subjected to hydrodynamic loads. In this context, an integrated model was developed and applied to two kinds of numerical analyses; one is to analyze periodic loading effect caused by pump pulsation and the other is to analyze random loading effect employing different turbulent models. Acoustic pressure distributions and flow velocity as well as pressure and temperature fields were calculated and compared to establish appropriate analysis techniques.

Key Words
hydrodynamic loads; pump pulsation frequency; reactor internals; turbulent models

Address
Da-Hye Kim, Yoon-Suk Chang : Kyung Hee University, Seocheon-dong, Giheung-gu, Yongin 446-701, Korea
Myung-Jo Jhung : Korea Institute of Nuclear Safety, Guseong-dong, Yuseong-gu, Daejeon 305-338, Korea

Abstract
Steel tubes have an efficient shape with large second moment of inertia relative to their light weight. One of the main problems of these members is their low buckling resistance caused from having thin walls. In this study, steel foams with high strength over weight ratio is used to fill the steel tube to beneficially modify the response of steel tubes. The linear eigenvalue and plastic collapse FE analysis is done on steel foam filled tube under pure compression and three point bending simulation. It is shown that steel foam improves the maximum strength and the ability of energy absorption of the steel tubes significantly. Different configurations with different volume of steel foam and composite behavior is investigated. It is demonstrated that there are some optimum configurations with more efficient behavior. If composite action between steel foam and steel increases, the strength of the element will improve, in a way that, the failure mode change from local buckling to yielding.

Key Words
steel foam; steel tube; plate buckling; imperfection; finite element analysis

Address
Mohammadreza Moradi : Department of Civil and Environmental Engineering, Old Dominion University, Norfolk, VA, 23529, USA
Sanjay R. Arwade : Department of Civil and Environmental Engineering, University of Massachusetts, Amherst, MA, 01003, USA

Abstract
Most existing damage detection methods based on curvature should investigate the indicator value changes between the intact and damaged state. However, the \'footprint\' in the intact state is usually not available for most actual beams. Therefore, a new damage localization indicator called Difference of Nearby Difference Curvature Indicator (DNDCI) was introduced for single-span beams. This indicator does not require prior information of the intact beam and is sensitive to the damage occurs on or nearby the measuring points. Practical and detailed application method of DNDCI has been proposed. Besides the idealized simply supported beams, it was validated by example that DNDCI is also applicable to the actual single-span beams supported by bearings.

Key Words
beam; damage; localization; curvature; displacement

Address
Yi-lin Wang : School of Civil Engineering, Shandong Jianzhu University, Jinan Shandong Province, P.R. China

Abstract
The article presents the methodology for finding material damping capacity at higher frequency and at relatively lower amplitudes. The Lamb wave dispersion theory and loss less finite element model is used to find the damping capacity of composite materials. The research has been focused on high frequency applications materials. The method was implemented on carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) plates. The Lamb waves were generated using ultrasonic pulse generator setup. The hybrid method has been explored in this article and the results have been compared with bandwidth methods available in the literature.

Key Words
lamb wave; acoustic emission; vibration; carbon fibers; glass fibers; damping

Address
B.S. Ben : Department of Mechanical Engineering, National Institute of Technology, Warangal, 506004, India
B.A. Ben : Department of Mechanical Engineering (AUCE), Andhra University, Visakhapatnam, 530003, India
S.H. Kweon and S.H. Yang : School of Mechanical Engineering, Kyungpook National University, Daegu 702-701,South Korea

Abstract
In this paper, three dimensional static and dynamic analyses of two dimensional functionally graded annular sector plates have been investigated. The material properties vary through both the radial and axial directions continuously. Graded finite element and Newmark direct integration methods have been used to solve the 3D-elasticity equations in time and space domains. The effects of power law exponents and different boundary conditions on the behavior of FGM annular sector plate have been investigated. Results show that using 2D-FGMs and graded elements have superiority over the homogenous elements and 1D-FGMs. The model has been compared with the result of a 1D-FGM annular sector plate and it shows good agreement.

Key Words
three dimensional elasticity; graded finite element method; 2D-FGM annular sector plate; static and dynamic analysis

Address
Kamran Asemi, Manouchehr Salehi and Mojtaba Sadighi : Mechanical Engineering Department, Amirkabir University of Technology, Tehran, Iran

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