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CONTENTS
Volume 61, Number 3, February10 2017
 

Abstract
This work presents a new strategy to model stress dependent relaxation process in large deformation. The strategy is relied on the fact that in some particular soft materials undergoing large deformation, e.g., elastomers, rubbers and soft tissues, the relaxation time depends strongly on stress levels. To simplify the viscoelastic model, we consider that the relaxation time is the function of previous elastic deviatoric stress state experienced by materials during loading. Using the General Maxwell Model (GMM), we simulate numerically conditions with the constant and the stress dependent relaxation time for uniaxial tension and compression loading. Hence, it can be shown that the proposed model herein not only can represent different relaxation time for different stress level but also maintain the capability of the GMM to model hysteresis phenomena.

Key Words
relaxation time; large deformation; incompressible; Maxwell element; stress dependent

Address
Sugeng Waluyo : Department of Industrial Engineering, University of Jenderal Soedirman
Jl. Mayjen Sungkono Km. 5, Blater, Purbalingga, 53371, Indonesia

Abstract
In the present study, a numerical model for probability analysis of optimal design of fatigue non-uniform crack growth behaviour of a cracked aluminium 2024 T3 plate repaired with a bonded composite patch is investigated. The proposed 3D numerical model has advanced in literatures, which gathers in a unique study: problems of reliability, optimization, fatigue, cracks and repair of plates subjected to tensile loadings. To achieve this aim, a finite element modelling is carried out to determine the evolution of the stress intensity factor at the crack tip Paris law is used to predict the fatigue life for a give n crack. To have an optimal volume of our patch satisfied the practical fatigue life, a procedure of optimization is proposed. Finally, the probabilistic analysis is performed in order to a show that optimized patch design is influenced by uncertainties related to mechanical and geometrical properties during the manufacturing process.

Key Words
composites; fatigue; optimizations; numerical methods; structural reliability; simulation, fracture mechanics

Address
H. Errouane, N. Deghoul, Z. Sereir :Laboratoire Structures de Composites et Materiaux innovants, Faculte de Genie Mecanique,
Universite des Sciences et de la Technologie d\'Oran, BP 1505 El M\'naouer, USTMB, Oran, Algerie
A. Chateauneuf:Clermont Universite, Blaise Pascal, EA 3867, LaMI, BP 10448, 63000 Clermont-Ferrand, France

Abstract
Free vibration analysis for continuous bridge under any number of vehicles is conducted in this paper. Calculation strategy for natural frequency and mode shape is proposed based on Euler-Bernoulli beam theory and numerical assembly method. Firstly, a half-car planar model is adopted; equations of motion and displacement functions for bridge and vehicle are established, respectively. Secondly, the undermined coefficient matrices for wheels, vehicles, intermediate support, left-end support and right-end support are derived. Then, the numerical assembly technique for conventional finite element method is adopted to construct the overall matrix of coefficients for whole system. Finally, natural frequencies and corresponding mode shapes are determined based on iterative method and overall matrix solution. Numerical simulation is presented to verify the effectiveness of the proposed method. The results reveal that the solutions of present method are exact ones. Natural frequencies and associate modal shapes of continuous bridge under different conditions of vehicles are investigated. The influences of vehicle parameters on natural frequencies are also demonstrated.

Key Words
continuous bridge; bridge-vehicle interaction; free vibration; numerical assembly method; numerical simulation

Address
Guojin Tan,Wensheng Wang, Yubo Jiao and Zhigang Wei : College of Transportation, Jilin University, Renmin Street 5988, Changchun 130022, China

Abstract
The applications of active control is being more popular nowadays. Several control algorithms have been developed to determine optimum control force. In this paper, a Chaotic Particle Swarm Optimization (CPSO) technique, based on Logistic map, is used to compute the optimum control force of active tendon system. A chaotic exploration is used to search the solution space for optimum control force. The response control of Multi-Degree of Freedom (MDOF) shear buildings, equipped with active tendons, is introduced as an optimization problem, based on Instantaneous Optimal Active Control algorithm. Three MDOFs are simulated in this paper. Two examples out of three, which have been previously controlled using Lattice type Probabilistic Neural Network (LPNN) and Block Pulse Functions (BPFs), are taken from prior works in order to compare the efficiency of the current method. In the present study, a maximum allowable value of control force is added to the original problem. Later, a twenty-story shear building, as the third and more realistic example, is considered and controlled. Besides, the required Central Processing Unit (CPU) time of CPSO control algorithm is investigated. Although the CPU time of LPNN and BPFs methods of prior works is not available, the results show that a full state measurement is necessary, especially when there are more than three control devices. The results show that CPSO algorithm has a good performance, especially in the presence of the cut-off limit of tendon force; therefore, can widely be used in the field of optimum active control of actual buildings.

Key Words
Chaotic Particle Swarm Optimization; logistic map; instantaneous optimal active control; active tendon system; shear buildings; LPNN; BPFs

Address
Saeed Asil Gharebaghi and Ehsan Zangooei : Civil Engineering Faculty, K. N. Toosi University of Technology, Tehran, Iran

Abstract
This study presents a particle swarm optimization algorithm integrated with weighted particle concept and improved fly-back technique. The rationale behind this integration is to utilize the affirmative properties of these new terms to improve the search capability of the standard particle swarm optimizer. Improved fly-back technique introduced in this study can be a proper alternative for widely used penalty functions to handle existing constraints. This technique emphasizes the role of the weighted particle on escaping from trapping into local optimum(s) by utilizing a recursive procedure. On the other hand, it guaranties the feasibility of the final solution by rejecting infeasible solutions throughout the optimization process. Additionally, in contrast with penalty method, the improved fly-back technique does not contain any adjustable terms, thus it does not inflict any extra ad hoc parameters to the main optimizer algorithm. The improved fly-back approach, as independent unit, can easily be integrated with other optimizers to handle the constraints. Consequently, to evaluate the performance of the proposed method on solving the truss weight minimization problems with discrete variables, several benchmark examples taken from the technical literature are examined using the presented method. The results obtained are comparatively reported through proper graphs and tables. Based on the results acquired in this study, it can be stated that the proposed method (integrated particle swarm optimizer, iPSO) is competitive with other metaheuristic algorithms in solving this class of truss optimization problems.

Key Words
optimization; truss structures; particle swarm optimization, weighted particle, constraint handling

Address
Ali Mortazavi and Ayhan Nuhoglu : Department of Civil Engineering, Ege University, 35100 İzmir, Turkey
Vedat Togan : Department of Civil Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey

Abstract
Modelling of a crack propagating through a finite element mesh under mixed mode conditions is of prime importance in fracture mechanics. In this paper, two crack growth criteria and the respective crack paths prediction in functionally graded materials (FGM) are compared. The maximum tangential stress criterion (et -criterion) and the minimum strain energy density criterion (S-criterion) are investigated using advanced finite element technique. Using Ansys Parametric Design Language (APDL), the variation continues in the material properties are incorporated into the model by specifying the material parameters at the centroid of each finite element. In this paper, the displacement extrapolation technique (DET) proposed for homogeneous materials is modified and investigated, to obtain the stress intensity factors (SIFs) at crack-tip in FGMs. Several examples are modeled to evaluate the accuracy and effectiveness of the combined procedure. The effect of the defects on the crack propagation in FGMs was highlighted.

Key Words
functionally graded materials; maximum tangential; strain energy density; crack propagation; displacement extrapolation technique; stress intensity factor

Address
Benamara Nabil, Boulenouar Abdelkader and Aminallah Miloud :Laboratory of Materials and Reactive Systems, Mechanical Engineering Department, Djillali Liabes University of Sidi Bel-Abbes,BP. 89, City Larbi Ben M\'hidi, 22000, Algeria


Abstract
In this paper we investigate the theory of micropolar thermoelastic bodies whose micro-particles possess microtemperatures. We transform the mixed initial boundary value problem into a temporally evolutionary equation on a Hilbert space and after that we prove the existence and uniqueness of the solution. We also approach the study of the continuous dependence of solution upon initial data and loads.

Key Words
micro-particles; microtemperatures; micropolar; semigroup; continuous dependence

Address
Marin Marin : Department of Mathematics and Computer Science, Transilvania University of Brasov, Romania
Dumitru Baleanu : Department of Mathematics and Computer Science, Cankaya University, Ankara, Turkey
,Institute of Space Sciences, Magurele - Bucharest, Romania
Sorin Vlase : Department of Mechanical Engineering, Transilvania University of Brasov, Romania

Abstract
Concrete pavements are subjected to traffic and environmental loadings. Repetitive type of such loading cause fatigue distress which leads to failure by forming cracks in pavement. Fatigue life of concrete pavement is calculated from the stress ratio (i.e. the ratio of applied flexural stress to the flexural strength of concrete). For the correct estimation of fatigue life, it is necessary to determine the maximum flexural tensile stress developed for practical loading conditions. Portland cement association PCA (1984) and Indian road congress IRC 58 (2015) has given charts and tables to determine maximum edge stresses for particular loading and subgrade conditions. It is difficult to determine maximum stresses for intermediate loading and subgrade conditions. The main purpose of this study is to simplify the analysis of rigid pavement without compromising the accuracy. Equations proposed for determination of maximum flexural tensile stress of pavement are verified by finite element analysis.

Key Words
concrete pavement; flexural stress; edge stress; slab thickness; radius of relative stiffness; simplified approach

Address
Rameshwar J. Vishwakarma and Ramakant K. Ingle : Department of Applied Mechanics, Visvesvaraya National Institute of Technology, Nagpur, India

Abstract
The use of fiber reinforced polymer (FRP) for torsional strengthening of reinforced concrete (RC) single cell box beams has been analyzed considerably by researchers worldwide. However, little attention has been paid to torsional strengthening of multicell box girders in terms of both experimental and numerical research. This paper reports the experimental work in an overall investigation for torsional strengthening of multicell box section RC girders with externally-bonded Carbon Fiber Reinforced Polymer CFRP strips. Numerical work was carried out using non-linear finite element modeling (FEM). Good agreement in terms of torque-twist behavior, steel and CFRP reinforcement responses, and crack patterns was achieved. The unique failure modes of all the specimens were modeled correctly as well.

Key Words
concrete torsion; multicell box girder; carbon fiber reinforced polymer; strengthened girders; finite elements; nonlinear analysis

Address
Abeer A. Majeed : Engineering Affairs Department, University of Baghdad, 17001 Baghdad, Iraq
Abbas A. Allawi : Department of Civil Engineering, University of Baghdad, 17001Baghdad, Iraq
Kian H. Chai : Department of Civil Engineering, Faculty of Engineering Building, University of Malaya, 50603 Kuala Lumpur, Malaysia
Hameedon W. Wan Badaruzzam : Department of Civil and Structural Engineering, Faculty of Engineering, Universiti Kebangsaan Malaysia,
43600 UKM Bangi, Selangor, Malaysia

Abstract
RC shear walls are considered one of the main lateral resisting members in buildings. In recent years, FRP has been widely utilized in order to strengthen and retrofit concrete structures. A number of experimental studies used CFRP sheets as an external bracing system for retrofitting of RC shear walls. It has been found that the common mode of failure is the debonding of the CFRP-concrete adhesive material. In this study, behavior of RC shear wall was investigated with three different micro models. The analysis included 2D model using plane stress element, 3D model using shell element and 3D model using solid element. To allow for the debonding mode of failure, the adhesive layer was modeled using cohesive surface-to-surface interaction model at 3D analysis model and node-to-node interaction method using Cartesian elastic-plastic connector element at 2D analysis model. The FE model results are validated comparing the experimental results in the literature. It is shown that the proposed FE model can predict the modes of failure due to debonding of CFRP and behavior of CFRP strengthened RC shear wall reasonably well. Additionally, using 2D plane stress model, many parameters on the behavior of the cohesive surfaces are investigated such as fracture energy, interfacial shear stress, partial bonding, proposed CFRP anchor location and using different bracing of CFRP strips. Using two anchors near end of each diagonal CFRP strips delay the end debonding and increase the ductility for RC shear walls.

Key Words
finite element model; RC shear walls; cohesive interaction; CFRP; strengthening; debonding

Address
Mohammed A. Sakr, Saher R. El-khoriby, Tarek M. Khalifa and Mohammed T. Nagib : Department of Structural Engineering, Tanta University, Tanta, Egypt

Abstract
Recently, the transportation of dangerous explosive goods is increasing, which makes vehicle blasting accidents a potential threat for the safety of bridge structures. In addition, blasting accidents happen more easily when earthquake occurs. Excessive dynamic response of bridges under extreme loads may cause local member damage, serviceability issues, or even failure of the whole structure. In this paper, a new explosion-proof and aseismic system is proposed including cable support damping bearing and steel-fiber reinforced concrete based on the existing researches. Then, considering one 40m-span simply supported concrete T-bridge as the prototype, through scale model test and numerical simulation, the dynamic response of the bridge under three conditions including only earthquake, only blast load and the combination of the two extreme loads is obtained and the applicability of this explosion-proof and aseismic system is explored. Results of the study show that this explosion-proof and aseismic system has good adaptability to seism and blast load at different level. The reducing vibration isolation efficiency of cable support damping bearing is pretty high. Increasing cables does not affect the good shock-absorption performance of the original bearing. The new system is good at shock absorption and displacement limitation. It works well in reducing the vertical dynamic response of beam body, and could limit the relative displacement between main girder and capping beam in different orientation so as to solve the problem of beam falling. The study also shows that the enhancement of steel fibers in concrete could significantly improve the blast resistance of main beam. Results of this paper can be used in the process of antiknock design, and provide strong theoretical basis for comprehensive protection and support of girder bridges.

Key Words
blast impact; earthquake; scale model test; cable support bearing; fiber reinforced concrete

Address
Jingyu Wang, Wancheng Yuan and Xun Wu : State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China
Kai Wei : University of Massachusetts, Amherst, MA 01003, USA

Abstract
This paper presents an experimental and analytical investigation on the behavior of a U-shaped girder subjected to operation, cracking and ultimate loads. A full-scale destructive test was conducted on a U-shaped girder to study the cracking process, load-carrying capacity, failure mechanism and load-deformation relationships. Accordingly, the tested U-shaped girder was modeled using ANSYS and a non-linear element analysis was conducted. The investigation shows that the U-shaped girder meets the specified requirements of vertical stiffness, cracking and ultimate load capacity. Unfavorable torsional effect is tolerable during operation. However, compared with box girders, the U-shaped girder has a more transverse mechanical effect and longitudinal cracks are apt to occur in the bottom slab.

Key Words
rail transit; U-shaped girder; experiment; finite element analysis; longitudinal crack

Address
Xun Wu and Hui Li : Department of Bridge Engineering, Tongji University, 1239 Siping Road, Shanghai, China


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