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CONTENTS
Volume 45, Number 4, February25 2013
 

Abstract
Complex structures are usually assembled from several substructures with joints connecting them together. These joints have significant effects on the dynamic behavior of the assembled structure and must be accurately modeled. In structural analysis, these joints are often simplified by assuming ideal boundary conditions. However, the dynamic behavior predicted on the basis of the simplified model may have significant errors. This has prompted the researchers to include the effect of joint stiffness in the structural model and to estimate the stiffness parameters using inverse dynamics. In the present work, structural joints have been modeled as a pair of translational and rotational springs and frequency equation of the overall system has been developed using sub-structure synthesis. It is shown that using first few natural frequencies of the system, one can obtain a set of over-determined system of equations involving the unknown stiffness parameters. Method of multi-linear regression is then applied to obtain the best estimate of the unknown stiffness parameters. The estimation procedure has been developed for a two parameter joint stiffness matrix.

Key Words
vibration; inverse dynamics; sub-structure synthesis; joint stiffness identification; linear parameters; multi-linear regression

Address
Sanjay B. Ingole: Government Polytechnic, Sadar,Nagpur 440001, India
Animesh Chatterjee: Visvesvaraya National Institute of Technology, Nagpur, 440010, India

Abstract
Hollow cylindrical tubes with a prismatic sandwich lining designed to replace the solid cross-sections are studied in this paper. The sections are divided by a number of revolving periodic unit cells and three topologies of unit cells (Square, Triangle and Kagome) are proposed. Some types of multiple-topology designed materials are also studied. The feasibility and accuracy of a homogenization method for obtaining the equivalent parameters are investigated. As the curved elements of a unit cell are represented by straight elements in the method and the ratios of the lengths of the curved elements to the lengths of the straight elements vary with the changing number of unit cells, some errors may be introduced. The frequencies of the first five modes and responses of the complete and equivalent models under an internal static pressure and an internal step pressure are compared for investigating the scope of applications of the method. The lower bounds and upper bounds of the number of Square, Triangular and Kagome cells in the sections are obtained. It is shown that treating the multiple-topology designed materials as a separate-layer structure is more accurate than treating the structure as a whole.

Key Words
sandwich tube; homogenization method; prismatic core; multiple-topology designed materials

Address
Kai Zhang: School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi\'an 710072, China; State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China
Zichen Deng: School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi\'an 710072, China; State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China
Huajiang Ouyang: School of Engineering, University of Liverpool, Liverpool L69 3GH, United Kingdom
Jiaxi Zhou: College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082, China

Abstract
RC flat plates that have no flexural stiffness by boundary beams may be governed by a serviceability as well as a strength condition. A construction sequence and its impact on the distributions of construction loads among slabs tied by shores are decisive factors influencing immediate and long term performances of flat plate. Over-loading and tensile cracking in early-aged slabs significantly increase the deflection of a flat plate system under construction. A reshoring work may be helpful in reducing slab deflections by controlling the vertical distributions of construction loads in a multi-shored flat plate system. In this study, a change of construction loads by reshoring works and its effects on deflections of flat plate systems under construction are analyzed. The slab construction loads with various reshoring schemes are defined by a simplified method, and the practical calculation of slab deflections with considering construction sequences and concrete cracking effects is applied. From parametric studies, the reshoring works are verified to reduce construction loads and slab deflections.

Key Words
flat plate; reshoring; deflection; construction load; reinforced concrete

Address
Su-Min Kang: Technology Research Institute, Daelim Industrial Co., Seoul, Republic of Korea
Tae-Sung Eom: Department of Architecture, Catholic University of Daegu, Gyeongbuk-do, Republic of Korea
Jae-Yo Kim: Department of Architectural Engineering, Kwangwoon University, Seoul, Republic of Korea

Abstract
In this paper, identification of isotropic and orthotropic linear elastic material constitutive parameters has been demonstrated by a FEA-free energy-based inverse analysis method. An important feature of the proposed method is that it requires no finite element (FE) simulation of the tested material. Full-field displacements calculated using digital image correlation (DIC) are used to compute DIC stress fields enforcing the equilibrium condition and DIC strain fields using interpolation functions. Boundary tractions and displacements are implicitly recast into an objective function that measures the energy residual of external work and internal elastic strain energy. The energy conservation principle states that the residual should be zero, and so minimizing this objective function inversely identifies the constitutive parameters. Synthetic data from simulated testing of isotropic materials and orthotropic composite materials under 2D plane stress conditions are used for verification of the proposed method. When identifying the constitutive parameters, it is beneficial to apply loadings in multiple directions, and in ways that create non-uniform stress distributions. The sensitivity of the parameter identification method to noise in both the measured full-field DIC displacements and loadings has been investigated.

Key Words
digital image correlation; constitutive law; inverse analysis; parameter identification; finite element; optimization; orthotropic material; anisotropic material

Address
Shen Shang and Gun Jin Yun: Department of Civil Engineering, The University of Akron, Akron, OH, 44325, USA
Shilpa Kunchumb and Joan Carletta: Department of Electrical & Computer Engineering, The University of Akron, Akron, OH, 44325, USA

Abstract
This paper investigates properties of integral operators in complex variable boundary integral equation in plane elasticity, which is derived from the Somigliana identity in the complex variable form. The generalized Sokhotski-Plemelj\' s formulae are used to obtain the BIE in complex variable. The properties of some integral operators in the interior problem are studied in detail. The Neumann and Dirichlet problems are analyzed. The prior condition for solution is studied. The solvability of the formulated problems is addressed. Similar analysis is carried out for the exterior problem. It is found that the properties of some integral operators in the exterior boundary value problem (BVP) are quite different from their counterparts in the interior BVP.

Key Words
properties of integral operators; complex variable boundary integral equation; Somigliana identity; interior boundary value problem; exterior boundary value problem

Address
Y.Z. Chen and Z.X. Wang: Division of Engineering Mechanics, Jiangsu University, Zhenjiang, Jiangsu, 212013 People\'s Republic of China

Abstract
In this study a truss model is used for the geometrically nonlinear static and dynamic analysis of a thin shallow arch subject to snap-through. Thanks to the very simple geometry of a truss, the equilibrium conditions can be easily written and the global stiffness matrix can be easily updated with respect to the deformed structure, within each step of the analysis. A very coarse discretization is applied; so, in a very simple way, the high frequency modes are suppressed from the beginning and there is no need to develop a complicated reduced-order technique. Two short computer programs have been developed for the geometrically nonlinear static analysis by displacement control of a plane truss model of a structure as well as for its dynamic analysis by the step-by-step time integration algorithm of trapezoidal rule, combined with a predictor-corrector technique. These two short, fully documented computer programs are applied on the geometrically nonlinear static and dynamic analysis of a specific thin shallow arch subject to snap-through.

Key Words
truss model; static nonlinear analysis; dynamic nonlinear analysis; snap-through; snap-back

Address
H. Xenidis and P.G. Papadopoulos: Department of Civil Engineering, Aristotle University of Thessaloniki 54124, Greece
K. Morfidis: Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki 55535, Greece

Abstract
This study explores the floor micro-vibrations induced by the automated guided vehicles (AGVs) in liquid-crystal-display (LCD) factories. The relationships between moving loads and both the vehicle weights and speeds were constructed by a modified Kanai-Tajimi (MKT) power spectral density (PSD) function whose best-fitting parameters were obtained through a regression analysis by using experimental acceleration responses of a small-scale three-span continuous beam model obtained in the laboratory. The AGV induced floor micro-vibrations under various AGV weights and speeds were then assessed by the proposed regressional MKT model. Simulation results indicate that the maximum floor micro-vibrations of the target LCD factory fall within the VC-B and VC-C levels when AGV moves at a lower speed of 1.0 m/s, while they may exceed the acceptable VC-B level when AGV moves at a higher speed of 1.5 m/s. The simulated floor micro-vibration levels are comparable to those of typical LCD factories induced by AGVs moving normally at a speed between 1.0 m/s and 2.0 m/s. Therefore, the numerical algorithm that integrates a simplified sub-structural multi-span continuous beam model and a proposed regressional MKT moving force model can provide a satisfactory prediction of AGV-induced floor micro-vibrations in LCD factories, if proper parameters of the MKT moving force model are adopted.

Key Words
micro-vibration; automated guided vehicle (AGV); liquid-crystal-display (LCD); moving loads; modified Kanai-Tajimi model; power spectral density (PSD)

Address
C.L. Lee and R.K.L. Su: Department of Civil Engineering, The University of Hong Kong, Hong Kong, China
Y.P. Wang: Department of Civil Engineering, National Chiao-Tung University, Hsinchu, Taiwan

Abstract
The free vibration of axially functionally graded tapered arches including shear deformation and rotatory inertia are studied through solving the governing differential equation of motion. Numerical results are presented for circular, parabolic, catenary, elliptic and sinusoidal arches with hinged-hinged, hinged-clamped and clamped-clamped end restraints. In this study Differential Quadrature element of lowest order (DQEL) or Lagrangian Interpolation technique is applied to solve the problems. Three general taper types for rectangular section are considered. The lowest four natural frequencies are calculated and compared with the published results.

Key Words
free vibration; axially functionally graded material; differential quadrature element method; tapered arch; frequency; boundary condition

Address
S. Rajasekaran: Department of Civil Engineering, PSG College of Technology, Coimbatore, Tamilnadu, India


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