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CONTENTS
Volume 73, Number 1, January10 2020
 

Abstract
Finite elements based on the partition of unity (PU) approximation have powerful capabilities for p-adaptivity and solutions with high smoothness without remeshing of the domain. Recently, the PU approximation was successfully applied to the three-node shell finite element, properly eliminating transverse shear locking and showing excellent convergence properties and solution accuracy. However, the enrichment with the PU approximation results in a significant increase in the number of degrees of freedom; therefore, it requires greater computational cost, thus making it less suitable for practical engineering. To circumvent this disadvantage, we propose a new strategy to decrease the total number of degrees of freedom in the existing PU-based shell element, without loss of optimal convergence and accuracy. To alleviate the locking phenomenon, we use the method of mixed interpolation of tensorial components and perform convergence studies to show the accuracy and capability of the proposed shell element. The excellent performances of the new shell elements are illustrated in three benchmark problems.

Key Words
partition of unity; shell finite element; three-node element; MITC method; convergence study; benchmark test

Address
1Department of Mechanical System Engineering, Jeonbuk National University, 567 Baekje-daero, Deokjin-gu,
Jeonju-si, Jeollabuk-do 54896, Republic of Korea
2Department of Biological Engineering, Massachusetts Institute of Technology,
77 Massachusetts Avenue, Cambridge, MA 02139, USA

Abstract
A finite element (FE) model for analyzing slender reinforced high-strength concrete (HSC) columns under biaxial eccentric loading is formulated in terms of the Euler-Bernoulli theory. The cross section of columns is divided into discrete concrete and reinforcing steel fibers so as to account for varied material properties over the section. The interaction between axial and bending fields is introduced in the FE formulation so as to take the large-displacement or P-delta effects into consideration. The proposed model aims to be simple, user-friendly, and capable of simulating the full-range inelastic behavior of reinforced HSC slender columns. The nonlinear model is calibrated against the experimental data for slender column specimens available in the technical literature. By using the proposed model, a numerical study is carried out on pin-ended slender HSC square columns under axial compression and biaxial bending, with investigation variables including the load eccentricity and eccentricity angle. The calibrated model is expected to provide a valuable tool for more efficiently designing HSC columns.

Key Words
slender columns; high-strength concrete; finite element method; biaxial bending

Address
Tiejiong Lou: Hubei Key Laboratory of Roadway Bridge & Structure Engineering, Wuhan University of Technology, 430070 Wuhan, China
Tiejiong Lou, Wei Sun: Faculty of Engineering and Physical Sciences, University of Southampton, SO17 1BJ Southampton, United Kingdom
Sergio M. R. Lopes, Adelino V. Lopes : Department of Civil Engineering, University of Coimbra, 3030-788 Coimbra, Portugal

Abstract
In rail industry, noise reduction is a concern to decrease environmental pollution. The current study focuses on rail damper modeling and improvement of the model through validation with experimental results. Accurate modeling and simulation of rail dampers, specifically tuned rail dampers with layers interconnected by bolt joints, shall enable objective-oriented improvement of their design. In this work, to improve the damper model cone pressure theory is applied in the FE model and the sensitivity analysis is then applied to gradually improve the FE model. The improved model yields higher Modal Assurance Criterion (MAC) values and lower frequencies deviation.

Key Words
rail damper; model updating; Modal Assurance Criterion (MAC); Finite Element Modeling; eigenfrequencies; eigenvectors

Address
Department of Structural Analysis, Institute of Mechanics, Technical University of Berlin, Str. d. 17. Juni 135, D - 10623 Berlin, Germany

Abstract
This paper investigates the free and forced longitudinal vibration of a double nanorod system using doublet mechanics theory. The doublet mechanics theory is a multiscale theory spanning between lattice dynamics and continuum mechanics. Equations of motion and boundary conditions for the double nanorod system are obtained using Hamilton\'s principle. Clamped-clamped and clamped-free boundary conditions are considered. Frequencies and dynamic displacements are determined to demonstrate the effects of length scale parameter of considered material and geometry of the nanorods. It is shown that frequencies obtained by the doublet mechanics theory are bounded from above (van Hove singularity) and unlike classical elasticity theory doublet mechanics theory predicts finite number of modes depending on the length of the nanotube. The present doublet mechanics results have been compared to molecular dynamics, experimental and nonlocal theory results and good agreement is observed between the present and other mentioned results. The difference between wave frequencies of graphite is less than 10% between doublet mechanics and experimental results near to the end of the first Brillouin zone.

Key Words
double nanorod system; doublet mechanics; free vibration; forced vibration

Address
Department of Mechanical Engineering, Trakya University, 22030, Edirne, Turkey

Abstract
In different high seismic regions around the world, many non-ductile existing reinforced concrete frame buildings, built without adequate seismic detailing requirements, have been damaged or collapsed after past earthquakes. The assessment and the retrofit of these non-ductile concrete structures is crucial theme of research for all the scientific community of engineers. In particular, a careful assessment of the existing building is fundamental for understanding the failure mechanisms that govern the collapse of the structure or the achievement of the recommended limit states. Based on the seismic assessment, the best retrofit strategy can be designed and applied to the structure. A school building located in Avellino province (Italy) is the case study. The analysis of seismic vulnerability carried out on the mentioned building has highlighted deficiencies in both static and seismic load conditions. The retrofit of the building has been designed based on different retrofit options in order to show the real retrofit design developed from the engineers to achieve the seismic safety of the building. The retrofit costs associated to structural operations are calculated for each case and have been summed up to the costs of the in situ tests. The paper shows a real retrofit design case study in which the best solution is chosen based on the results in terms of structural performance and cost among the different retrofit options.

Key Words
seismic retrofit, RC jacketing, steel jacketing, FRP wrapping, retrofit costs

Address
Department of Structures for Engineering and Architecture, University of Naples Federico II, Naples, Italy

Abstract
The present work describes a new time marching procedure for structural dynamics analyses. In this novel technique, time integration parameters are automatically evaluated according to the properties of the model. Such parameters are locally defined, allowing the user to input a numerical dissipation property for each element, which defines the amount of numerical dissipation to be introduced. Since the integration parameters are locally defined as a function of the structural element itself, the time marching technique adapts according to the model, providing enhanced accuracy. The new methodology is based on displacement-velocity relations and no computation of accelerations is required. Furthermore, the method is second order accurate, it has guaranteed stability, it is truly self-starting and it allows highly controllable algorithm dissipation in the higher modes. Numerical results are presented and compared to those provided by the Newmark and the Bathe methods, illustrating the good performance of the new time marching procedure.

Key Words
structural dynamics; time marching; adaptive analyses; local parameters; controllable dissipation

Address
Tales Vieira Sofiste, and Webe João Mansur: Civil Engineering Department, COPPE, Federal University of Rio de Janeiro. Modeling Methods in Engineering and Geophysics Laboratory - LAMEMO, Rio de Janeiro, RJ, Brazil
Delfim Soares Jr : Structural Engineering Department, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil

Abstract
In this study, the problem of torsion of bars with open cross section surrounded by corrugated boundaries is analyzed. An approximate analytical solution is given using perturbation technique. First, the stress analysis for circular open cross-section for arbitrary opening angle is formulated and the problem is analytically solved. Second, the open cross-section with corrugated cross section is analyzed using perturbation method. First order contributions to the stresses and the torques have been added. The results have been exemplified and compared by considering special examples.

Key Words
torsion, circular, open cross section, corrugated surface, stress, perturbation

Address
Yaşar Pala: Uludag University, Engineering Faculty, Gorukle 16059, Bursa-Turkey
Abdullah Pala: Bursa Technical University, Engineering Faculty, Department of Mechatronics, Bursa-Turkey

Abstract
In this work, a mathematical model of beam-column system carrying a double eccentric end mass system is investigated, and solved analytically based on the exact solution analysis. The model considers the case in which the double eccentric end mass is a rigid storage tank containing fluid. Both Timoshenko and Bernoulli-Euler beam bending theories are considered. Equation of motion, general solution and boundary conditions for the present system model are developed and presented in dimensional and non-dimensional format. Several important non-dimensional design parameters are introduced. Symbolic and/or explicit formulae of the frequency and mode shape equations are formulated. To the authors knowledge, the present reduced closed form symbolic and explicit frequency equations have not appeared in literature. For different applications, the results are validated using commercial finite element package, namely ANSYS. The beam-column system investigated in this paper is significant for many engineering applications, especially, in mechanical and structural systems.

Key Words
thick beam-column, free vibration, exact solution, tank with fluid, eccentric mass

Address
Department of Mechanical Design, Faculty of Engineering, Mataria, Helwan University,P.O. Box 11718, Helmeiat-Elzaton, Cairo, Egypt

Abstract
This study presents a 4 node, 11 DOF/node plate element based on higher order shear deformation theory for lamina composite plates. The theory accounts for parabolic distribution of the transverse shear strain through the thickness of the plate. Differential field equations of composite plates are obtained from energy methods using virtual work principle. Differential field equations of composite plates are obtained from energy methods using virtual work principle. These equations were transformed into the operator form and then transformed into functions with geometric and dynamic boundary conditions with the help of the Gâteaux differential method, after determining that they provide the potential condition. Boundary conditions were determined by performing variational operations. By using the mixed finite element method, plate element named HOPLT44 was developed. After coding in FORTRAN computer program, finite element matrices were transformed into system matrices and various analyzes were performed. The current results are verified with those results obtained in the previous work and the new results are presented in tables and graphs.

Key Words
composite plate; high order shear deformation theory; finite element method; static analysis; energy principle

Address
Emrah Madenci: Department of Civil Engineering, Faculty of Engineering and Architecture, Necmettin Erbakan University, 42140 Konya, Turkey
Atilla Özütok: Department of Civil Engineering, Faculty of Engineering, KTO Karatay University, 42020 Konya, Turkey


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