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CONTENTS
Volume 72, Number 2, October25 2019
 

Abstract
The effect of galleries on the earthquake behavior of dams should be investigated to obtain more realistic results. Therefore, a roller compacted concrete (RCC) dam with and without galleries are examined under ground motion effects. For this purpose, Cine RCC dam constructed in AydIn, Turkey, is selected in applications. The optimal mesh around galleries is investigated to obtain the most realistic results. Two-dimensional finite element models of Cine RCC dam with and without galleries are prepared by using ANSYS software. Empty and full reservoir conditions were taken into account in the time-history analyses. Hydrodynamic effect of the reservoir water was taken into account considering two-dimensional fluid finite elements based on the Lagrangian approach. It is examined that how principle stresses and displacements change by height and during earthquake. The dam-foundation-reservoir interaction was taken into consideration with contact-target element pairs. The displacements and principle stress components obtained from the linear analyses are compared each other for various cases of reservoir water and galleries. According to numerical analyses, the effect of galleries is clear on the response of RCC dam. Besides, hydrodynamic water effect obviously increases the principle stress components and horizontal displacements of the dam.

Key Words
Dynamic analysis of dams; gallery; Lagrangian approach; mesh optimization; roller compacted concrete dam

Address
Muhammet Karabulut /Zonguldak Bulent Ecevit University
Murat Emre Kartal/Izmir Democracy University


Abstract
This paper presents the results of an experimental investigation on the compressive strength of small scale concentrically axially loaded fiber-reinforced polymer (FRP) confined plain concrete columns, with cylinder concrete strength 19 MPa. For columns with circular (150-mm diameter) and square (150-mm side) cross sections wrapped with glass- and carbon- FRP sheets (GFRP and CFRP, respectively) applied with dry lay-up the effect of different jacket schemes and different overlap configurations on the confined characteristics is investigated. Test results indicate that the most cost effective jacket configuration among those tested is for one layer of CFRP, for both types of sections. In square sections the location of the lap length, either in the corner or along the side, does not seem to affect the confined performance. Furthermore, in circular sections, the presence of an extra wrap with FRP fibers parallel to the column\'s axis enhances the concrete strength proportionally to the axial rigidity of the FRP jacket. The recorded strains and the distributions of lateral confining pressures are discussed. Existing design equations are used to assess the lateral confining stresses and the confined concrete strength making use of the measured hoop strains.

Key Words
columns, concrete, cylinders, cubes, fiber reinforced polymer (FRP), overlap, fiber orientation, effectiveness of confinement

Address
Marina L. Moretti/National Technical University of Athens

Abstract
The underlying mechanism of the wind-induced vibration of the hangers of the suspension bridges is still not fully understood at present and hence is comprehensively examined in this study. More specifically, a series of field measurements on the No. 2 hanger of the Xihoumen Bridge was first carefully conducted. Large amplitude vibrations of the hanger were found and the oscillation amplitude of the leeward cable was obviously larger than that of the windward cables. Furthermore, the trajectory of the leeward cable was close to an ellipse, which agreed well with the major characteristics of wake-induced vibration. Then, a theoretical model for the wake-induced vibration based on a 3-D continuous cable was established. To obtain the responses of the leeward cable, the finite difference method (FDM) was adopted to numerically solve the established motion equation. Finally, numerical simulations by using the structural parameters of the No. 2 hanger of the Xihoumen Bridge were carried out within the spatial range of 4 4<=X<=10 and 0<=Y<=4 with a uniform interval of delta X= delta Y=0.25. The results obtained from numerical simulations agreed well with the main features obtained from the field observations on the Xihoumen Bridge. This observation indicates that the wake-induced vibration might be one of the reasons for the hanger oscillation of the suspension bridge. In addition, the effects of damping ratio and windward cable movement on the wake-induced vibration of the leeward cable were numerically investigated.

Key Words
hangers of suspension bridges, wake-induced vibration, field measurements, theoretical analyses, structural damping

Address
Shouying Li/Hunan University
Yangchen Deng/Hunan University
Xu Lei/Hunan University
Teng Wu/University at Buffalo
Zheng Qing Chen/Hunan University

Abstract
Topology optimization of structures seeking the best distribution of mass in a design space to improve the structural performance and reduce the weight of a structure is one of the most comprehensive issues in the field of structural optimization. In addition to structures stiffness as the most common objective function, frequency optimization is of great importance in variety of applications too. In this paper, an efficient multi-objective Bi-directional Evolutionary Structural Optimization (BESO) method is developed for topology optimization of frequency and stiffness in continuum structures simultaneously. A software package including a Matlab code and Abaqus FE solver has been created for the numerical implementation of multi-objective BESO utilizing the weighted function method. At the same time, by considering the weaknesses of the optimized structure in single-objective optimizations for stiffness or frequency problems, slight modifications have been done on the numerical algorithm of developed multi-objective BESO in order to overcome challenges due to artificial localized modes, checker boarding and geometrical symmetry constraint during the progressive iterations of optimization. Numerical results show that the proposed Multiobjective BESO method is efficient and optimal solutions can be obtained for continuum structures based on an existent finite element model of the structures.

Key Words
topology optimization, stiffness problem, frequency problem, BESO, Multiobjective

Address
Mohsen Teimouri/K. N. Toosi University of Technology
Masoud Asgari/K. N. Toosi University of Technology

Abstract
Finite element analysis is one of the most used tools for studying femoral neck fracture. Nerveless, consensus concerning either the choice of material characteristics, damage law and /or geometric models (linear on nonlinear) remains unreached. In this work, we propose a numerical quasi-brittle damage model to describe the behavior of the proximal femur associated with two methods to evaluate the Young modulus. Eight proximal femur finite elements models were constructed from CT scan data (4 donors: 3 women; 1 man). The numerical computations showed a good agreement between the numerical curves (load – displacement) and the experimental ones. A very encouraging result is obtained when a comparison is made between the computed fracture loads and the experimental ones (R2=0.825, Relative error =6.49%). All specific numerical computation provided very fair qualitative matches with the fracture patterns for the sideway fall simulation. Finally, the comparative study based on 32 simulations adopting linear and nonlinear meshing led to the conclusion that the quantitatively results are improved when a nonlinear mesh is used.

Key Words
Sideway fall, proximal femur fracture, quasi-brittle damage, finite element analysis, fracture pattern, non-linear meshing

Address
Zahira Nakhli/Laboratoire de Recherche Matériaux Mesures et Application
Fafa Ben Hatir/Laboratoire de Recherche Matériaux Mesures et Application
Martine Pithioux/Aix Marseille University
Patrick Chabrand/Aix Marseille University
Khemais Saanouni/Laboratoire des Systèmes Mécaniques et d

Abstract
Reliability analysis of composite structures considering random variation of involved parameters is quite important as composite materials revealed large statistical variations in their mechanical properties. The reliability analysis of such structures by the first order reliability method (FORM) and Monte Carlo Simulation (MCS) based approach involves repetitive evaluations of performance function. The response surface method (RSM) based metamodeling technique has emerged as an effective solution to such problems. In the application of metamodeling for uncertainty quantification and reliability analysis of composite structures; the finite element model is usually formulated by either classical laminate theory or first order shear deformation theory. But such theories show significant error in calculating the structural responses of composite structures. The present study attempted to apply the RSM based MCS for reliability analysis of composite shell structures where the surrogate model is constructed using higher order shear deformation theory (HSDT) of composite structures considering the uncertainties in the material properties, load, ply thickness and radius of curvature of the shell structure. The sensitivity of responses of the shell is also obtained by RSM and finite element method based direct approach to elucidate the advantages of RSM for response sensitivity analysis. The reliability results obtained by the proposed RSM based MCS and FORM are compared with the accurate reliability analysis results obtained by the direct MCS by considering two numerical examples.

Key Words
reliability, response surface method, laminated shell, higher order shear deformation theory, finite element analysis

Address
Sandipan N. Thakur/The University of Burdwan
Subrata Chakraborty/Indian Institute of Engineering Science and Technology
Chaitali Ray/Indian Institute of Engineering Science and Technology

Abstract
The methodology known as \"shape sensing\" allows the reconstruction of the displacement field of a structure starting from strain measurements, with considerable implications for structural monitoring, as well as for the control and implementation of smart structures. An approach to shape sensing is based on the inverse Finite Element Method (iFEM) that uses a variational principle enforcing a least-squares compatibility between measured and analytical strain measures. The structural response is reconstructed without the knowledge of the mechanical properties and load conditions but based only on the relationship between displacements and strains. In order to efficiently apply iFEM to the most common structural typologies of civil engineering, its formulation according to the kinematical assumptions of the Bernoulli-Euler theory is presented. Two beam inverse finite elements are formulated for different loading conditions. Depending on the type of element, the relationship between the minimum number of required measurement stations and the interpolation order is defined. Several examples representing common applications of civil engineering and involving beams and frames are presented. To simulate the experimental strain data at the station points and to verify the accuracy of the displacements obtained with the iFEM shape sensing procedure, a direct FEM analysis of the considered structures is performed using the LUSAS software.

Key Words
shape sensing, iFEM, Euler-Bernoulli theory, structural monitoring, displacements

Address
Pierclaudio Savino/Politecnico di Torino
Marco Gherlone/Politecnico di Torino
Francesco Tondolo/Politecnico di Torino

Abstract
Weak form integral equations are developed to investigate the flapwise bending vibration of the rotating beams. Rayleigh and Eringen nonlocal elasticity theories are used to investigate the rotatory inertia and Size-dependency effects on the flapwise bending vibration of the rotating cantilever beams, respectively. Through repetitive integrations, the governing partial differential equations are converted into weak form integral equations. The novelty of the presented approach is the approximation of the mode shape function by a power series which converts the equations into solvable one. Substitution of the power series into weak form integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of the non-trivial solution for resulting system of equations. Accuracy of the proposed method is verified through several numerical examples, in which the influence of the geometry properties, rotatory inertia, rotational speed, taper ratio and size-dependency are investigated on the natural frequencies of the rotating beam. Application of the weak form integral equations has made the solution simpler and shorter in the mathematical process. Presented relations can be used to obtain a close-form solution for quick calculation of the first five natural frequencies of the beams with flapwise vibration and non-local effects. The analysis results are compared with those obtained from other available published references.

Key Words
flapwise, size-dependency, weak form integral equation, natural frequency, Rayleigh beam, nonlocal elasticity theory

Address
Mehrdad Mohammadnejad/Birjand University of Technology
Hamed Saffari/Shahid Bahonar University of Kerman

Abstract
The experimentally determined mechanical behavior of the material under the prescribed service conditions is the basis of advanced engineering optimum design. To allow experimental data on the behavior of the material considered, uniaxial stress tests were made. The aforementioned tests have enabled the determination of mechanical properties of material at different temperatures, then, the material\'s resistance to creep at various temperatures and stress levels, and finally, insight into the uniaxial high cyclic fatigue of the material under different applied stresses for prescribed stress ratio. Based on fatigue tests, using modified staircase method, fatigue limit was determined. All these data contributes the reliability of the use of material in mechanical structures. Data representing mechanical properties are shown in the form of engineering stress-strain diagrams; creep behavior is displayed in the form of creep curves while fatigue of the material is presented in the form of S-N (maximum applied stress versus number of the cycles to failure) curve. Material under consideration was 18CrNi8 (1.5920) steel. Ultimate tensile strength and yield strength at room temperature and at temperature of 600 degree celcius: [sigma m,20/600=(613/156)MPa; sigma0.2,20/600=(458/141)MPa], as well as endurance (fatigue) limit at room temperature and stress ratio of R=-1: (sigmaf,20,R=−1 = 285.1MPa).

Key Words
Steel 18CrNi8, mechanical properties, creep behavior and creep modeling, fatigue and fatigue limit

Address
Josip Brnic/University of Rijeka
Sanjin Krscanski/University of Rijeka
Marino Brcic/University of Rijeka
Lin Geng/Harbin Institute of Technology
Jitai Niu/Harbin Institute of Technology
Biao Ding/Shanghai University

Abstract
In this paper, the mechanical behaviour of functionally graded material beams is studied using the 3D Saint-Venant\'s theory, in which the section is free to warp in and out of its plane (Poisson\'s effects and out-of-plane warpings). The material properties of the FGM beam are distributed continuously through the thickness by several distributions, such as power-law distribution, exponential distribution, Mori-Tanaka schema and sigmoid distribution. The proposed method has been applied to study a simply supported FGM beam. The numerical results obtained are compared to other models in the literature, which show a high performance of the 3D exact theory used to describe the stress and strain fields in FGM beams.

Key Words
functionally graded material, ceramic, metal, modelling, beam, Saint-Venant theory, mechanical behaviour

Address
Mourad Khebizi/Mentouri University of Constantine
Hamza Guenfoud/University of Guelma
Mohamed Guenfoud/University of Guelma
Rached El Fatmi/National Engineering School of Tunis

Abstract
In a super-large underground with \"large span and high side wall\", it is buried in mountains with uneven lithology, complicated geostress field and developed geological structure. These surrounding rocks are more susceptible to stability issues during the construction period. This paper takes the left bank of Baihetan hydropower station (span is 34m) as a case study example, wherein the deformation mechanism of surrounding rock appears prominent. Through analysis of geological, geophysical, construction and monitoring data, the deformation characteristics and factors are concluded. The failure mechanism, spatial distribution characteristics, and evolution mechanism are also discussed, where rock mechanics theory, FLAC3D numerical simulation, rock creep theory, and the theory of center point are combined. In general, huge underground cavern stability issues has arisen with respect to huge-scale and adverse geological conditions since settling these issues will have milestone significance based on the evolutionary pattern of the surrounding rock and the correlation analyses, the rational structure of the factors, and the method of nonlinear regression modeling with regard to the construction and development of hydropower engineering projects among the worldwide.

Key Words
hydropower station, underground engineering, surrounding rock deformation, multi-point displacement, monitoring model

Address
Zhenhua Tian/China Institute of Water Resources and Hydropower Research
Jian Liu/Yalong River Hydropower Development Co
Xiaogang Wang/State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin
Lipeng Liu/State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin
Xiaobo Lv/Luoyun Water Project Management Division of Jiangsu province
Xiaotong Zhang/Luoyun Water Project Management Division of Jiangsu province


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