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CONTENTS
Volume 67, Number 2, July25 2018
 

Abstract
To improve the prediction accuracy of the strong-unloading rock slope performance and obtain the range of variation in the slope displacement, a new displacement time-series prediction model is proposed, called the fuzzy information granulation (FIG)-genetic algorithm (GA)-back propagation neural network (BPNN) model. Initially, a displacement time series is selected as the training samples of the prediction model on the basis of an analysis of the causes of the change in the slope behavior. Then, FIG is executed to partition the series and obtain the characteristic parameters of every partition. Furthermore, the later characteristic parameters are predicted by inputting the earlier characteristic parameters into the GA-BPNN model, where a GA is used to optimize the initial weights and thresholds of the BPNN; in the process, the numbers of input layer nodes, hidden layer nodes, and output layer nodes are determined by a trial method. Finally, the prediction model is evaluated by comparing the measured and predicted values. The model is applied to predict the displacement time series of a strong-unloading rock slope in a hydropower station. The engineering case shows that the FIG-GA-BPNN model can obtain more accurate predicted results and has high engineering application value.

Key Words
unloading rock slope; displacement prediction; fuzzy information granulation; genetic algorithm; back propagation neural network

Address
Ting Jiang, Zhenzhong Shen, Meng Yang, Liqun Xu and Lei Gan:
1) State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China
2) College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China
3) National Engineering Research Center of Water Resources Efficient Utilization and Engineering Safety, Hohai University,
Nanjing 210098, China
Xinbo Cui: Information Center of Land and Resources, Binzhou City, Binzhou, China

Abstract
By using the first order shear deformation plate theory (FSDT) in the present paper, the effect of porosity on the buckling behavior of carbon nanotube-reinforced composite porous plates has been investigated analytically. Two types of distributions of uniaxially aligned reinforcement material are utilized which uniformly (UD-CNT) and functionally graded (FG-CNT) of plates. The analytical equations of the model are derived and the exact solutions for critical buckling load of such type\'s plates are obtained. The convergence of the method is demonstrated and the present solutions are numerically validated by comparison with some available solutions in the literature. The central thesis studied and discussed in this paper is the Influence of Various parameters on the buckling of carbon nanotube-reinforced porous plate such as aspect ratios, volume fraction, types of reinforcement, the degree of porosity and plate thickness. On the question of porosity, this study found that there is a great influence of their variation on the critical buckling load. It is revealed that the critical buckling load decreases as increasing coefficients of porosity.

Key Words
nanotubes; buckling; shear deformation; porosity; plate

Address
Habib Guessas and Mustapha Meradjah: Laboratory of Materials et Hydrology, University of Sidi Bel Abbes, BP 89 Cite Ben M\'hidi, 22000 Sidi Bel Abbes, Algeria
Mohamed Zidour:
1) Universite Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algeria
2) Laboratory of Geomatics and Sustainable Development, Ibn Khaldoun University of Tiaret, Algeria
Abdelouahed Tounsi:
1) Laboratory of Materials et Hydrology, University of Sidi Bel Abbes, BP 89 Cite Ben M\'hidi, 22000 Sidi Bel Abbes, Algeria
2) Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
This study deals with buckling analysis with stretching effect of functionally graded carbon nanotube-reinforced composite beams resting on an elastic foundation. The single-walled carbon nanotubes (SWCNTs) are aligned and distributed in polymeric matrix with different patterns of reinforcement. The material properties of the CNTRC beams are estimated by using the rule of mixture. The significant feature of this model is that, in addition to including the shear deformation effect and stretching effect it deals with only 4 unknowns without including a shear correction factor. The equilibrium equations have been obtained using the principle of virtual displacements. The mathematical models provided in this paper are numerically validated by comparison with some available results. New results of buckling analyses of CNTRC beams based on the present theory with stretching effect is presented and discussed in details. the effects of different parameters of the beam on the buckling responses of CNTRC beam are discussed.

Key Words
buckling; stretching effect; CNTRC beams; elastic foundation

Address
Zoubida Khelifa:
1) Department of Civil Engineering, Ibn Khaldoun University, BP 78 Zaaroura, Tiaret (14000), Algeria
2) Department of Civil Engineering, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria
Lazreg Hadji and Tahar Hassaine Daouadji:
1) Department of Civil Engineering, Ibn Khaldoun University, BP 78 Zaaroura, Tiaret (14000), Algeria
2) Laboratory of Geomatics and Sustainable Development, Ibn Khaldoun University of Tiaret, Algeria
Mohamed Bourada: Department of Civil Engineering, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Algeria

Abstract
The perfobond connector, composed of a steel plate with a number of holes, serves as a certain type of shear connector in steel and concrete composite structures. Depending on limits in hole distances and rib heights, various hole shapes including circular-hole and long-hole are alternatives for perfobond connectors. This study presented the results of tests performed on 72 push-out specimens with perfobond connectors. The purpose was to evaluate the shear strength of perfobond connectors with circular-hole and long-hole. The effects of various parameters were investigated, including the hole diameter, the hole length, the hole height, the concrete strength, the existence, diameter and strength of rebar in the hole, the thickness, height and distance of perfobond ribs, and the thickness of concrete slabs. On the basis of 132 push-out test results in references and in this study, an analytical model was proposed by regression analysis to predict the shear strength of perfobond connectors. The proposed equation agreed reasonably well with the experimental results of perfobond connectors with different hole shapes.

Key Words
composite structures; perfobond connector; shear strength; push-out test; circular-hole; long-hole

Address
Shuangjie Zheng: College of Civil Engineering, Huaqiao University, Xiamen 361021, China
Chen Zhao: Shanghai Municipal Engineering Design Institute (Group) Co., Ltd., Shanghai 200092, China
Yuqing Liu: Department of Bridge Engineering, Tongji University, Shanghai 200092, China

Abstract
Thermal buckling of nonlocal flexoelectric nanoplates incorporating surface effects is analyzed for the first time. Coupling of strain gradients and electrical polarizations is introduced by flexoelectricity. It is assumed that flexoelectric nanoplate is subjected to uniform and linear temperature distributions. Long range interaction between atoms of nanoplate is modeled via nonlocal elasticity theory. The residual surface stresses which are usually neglected in modeling of flexoelectric nanoplates are incorporated into nonlocal elasticity to provide better understanding of the physic of problem. A Galerkin-based approach is implemented to solve the governing equations derived from Hamilton\'s principle are solved. The verification of obtained results is performed by comparing buckling loads of flexoelectric nanoplate with previous data. It is shown that buckling loads of flexoelectric nanoplate are significantly affected by thermal loading type, temperature change, nonlocal parameter, surface effect, plate thickness and boundary conditions.

Key Words
thermal buckling; flexoelectric nanoplate; surface effect; nonlocal elasticity theory

Address
Farzad Ebrahimi and Mohammad Reza Barati: Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, P.O.B. 16818-34149, Qazvin, Iran

Abstract
The Early-age construction loading and changing properties of concrete, especially in the multi-story structures can affect the slab deflection, significantly. Based on previously conducted experiment on eight simply-supported one-way slabs this paper investigates the effect of concrete type, fiber type and content, loading value, cracking moment, ultimate moment and applied moment on the instantaneous deflection of Self-Compacting Concrete (SCC) slabs. Two distinct loading levels equal to 30% and 40% of the ultimate capacity of the slab section were applied on the slabs at the age of 14 days. A wide range of the existing models of the effective moment of inertia which are mainly developed for conventional concrete elements, were investigated. Comparison of the experimental deflection values with predictions of the existing models shows considerable differences between the recorded and estimated instantaneous deflection of SCC slabs. Calculated elastic deflection of slabs at the ages of 14 and 28 days were also compared with the experimental deflection of slabs. Based on sensitivity analysis of the effective parameters, a new model is proposed and verified to predict the effective moment of inertia in SCC slabs with and without fiber reinforcing under two different loading levels at the age of 14 days.

Key Words
instantaneous deflection; early-age loading; one-way slab; reinforcement ratio; self-compacting concrete; effective moment of inertia; mixture design; fiber reinforcement; cracking moment; moment capacity; service moment

Address
Behnam Vakhshouri and Shami Nejadi: Faculty of Engineering and Information Technology, School of Civil and Environmental Engineering, University of Technology Sydney, Australia


Abstract
A simple predicted model using a modified Shear-lag method was used to represent the moisture absorption effect on the stiffness degradation for [0/90]2s composite laminates with transverse cracks and under flexural loading. Good agreement is obtained by comparing the prediction model and experimental data published by Smith and Ogin (2000). The material properties of the composite are affected by the variation of temperature and moisture absorption. The transient and non-uniform moisture concentration distribution give rise to the transient elastic moduli of cracked composite laminates. The hygrothermal effect is taken into account to assess the changes in the normalised axial and flexural modulus due to transverse crack. The obtained results represent well the dependence of the stiffness properties degradation on the cracks density, moisture absorption and operational temperature. The composite laminate with transverse crack loaded in axial tension is more affected by the hygrothermal condition than the one under flexural loading. Through this theoretical study, we hope to contribute to the understanding of the moisture absorption on the composite materials with matrix cracking.

Key Words
absorption; bending; transverse cracks; hygrothermal effect; stiffness; Chamis model

Address
M. Khodjet-Kesba, A. Benkhedda and B. Boukert: Laboratoire des Sciences Aeronautiques, Institut d\'Aeronautique et des Etudes Spatiales, Universite de Blida1, Blida, Algerie
E.A. Adda Bedia: Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, Sidi Bel Abbes, Algerie

Abstract
This research deals with the wave dispersion analysis of functionally graded double-layered nanobeam systems (FG-DNBSs) considering the piezoelectric effect based on nonlocal strain gradient theory. The nanobeam is modeled via Euler-Bernoulli beam theory. Material properties are considered to change gradually along the nanobeams\' thickness on the basis of the rule of mixture. By implementing a Hamiltonian approach, the Euler-Lagrange equations of piezoelectric FG-DNBSs are obtained. Furthermore, applying an analytical solution, the dispersion relations of smart FG-DNBSs are derived by solving an eigenvalue problem. The effects of various parameters such as nonlocality, length scale parameter, interlayer stiffness, applied electric voltage, relative motions and gradient index on the wave dispersion characteristics of nanoscale beam have been investigated. Also, validity of reported results is proven in the framework of a diagram showing the convergence of this model\'s curve with that of a previous published attempt.

Key Words
wave propagation; functionally graded double-layered nanobeam systems (FG-DNBSs); smart materials; non-local strain gradient piezoelectricity

Address
F. Ebrahimi and P. Haghi: Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, P.O.B. 16818-34149, Qazvin, Iran
A. Dabbagh: School of Mechanical Engineering, College of Engineering, University of Tehran, P.O.B. 4563-11155, Tehran, Iran

Abstract
This paper studies the non-axisymmetric 3D problem on the dynamics of the moving load acting in the interior of the hollow cylinder surrounded with elastic medium and this study is made by utilizing the exact equations of elastodynamics. It is assumed that in the interior of the cylinder the point located with respect to the cylinder axis moving forces act and the distribution of these forces is non-axisymmetric and is located within a certain central angle. The solution to the problem is based on employing the moving coordinate method, on the Fourier transform with respect to the spatial coordinate indicated by the distance of the point on the cylinder axis from the point at which the moving load acts, and on the Fourier series presentation of the Fourier transforms of the sought values. Numerical results on the critical moving velocity and on the distribution of the interface normal and shear stresses are presented and discussed. In particular, it is established that the non-axisymmetricity of the moving load can decrease significantly the values of the critical velocity.

Key Words
non-axisymmetric moving load; critical velocity; hollow cylinder; elastic medium; interface stresses; Fourier series

Address
S. D. Akbarov:
1) Department of Mechanical Engineering, Faculty of Mechanical Engineering, Yildiz Technical University, Yildiz Campus, 34349 Besiktas, Istanbul, Turkey
2) Institute of Mathematics and Mechanics, National Academy of Science of Azerbaijan, AZ1141, Baku, Azerbaijan
M.A. Mehdiyev: Department of Mathematics, Azerbaijan State University of Economics (UNEC), 1001, Baku, Azerbaijan
M. Ozisik: Department of Mathematical Engineering, Faculty of Chemistry and Metallurgy, Yildiz Technical University,
Davutpasa Campus, 34220, Esenler, Istanbul, Turkey

Abstract
In past years, numerous problems have vexed engineers with regard to buckling, corrosion, bending, and over-loading in damaged steel structures. This article sets out to investigate the possible effects of carbon fiber reinforced polymer (CFRP) and steel plates for retrofitting deficient steel square hollow section (SHS) columns. The effects of axial loading, stiffness, axial displacement, the position and shape of deficient region on the length of steel SHS columns, and slenderness ratio are examined through a detailed parametric study. A total of 14 specimens was tested for failure under axial compression in a laboratory and simulated using finite element (FE) analysis based on a numerical approach. The results indicate that the application of CFRP sheets and steel plates also caused a reduction in stress in the damaged region and prevented or retarded local deformation around the deficiency. The findings showed that a deficiency leads to reduced load-carrying capacity of steel SHS columns and the retrofitting method is responsible for the increase in the load-bearing capacity of the steel columns. Finally, this research showed that the CFRP performed better than steel plates in compensating the axial force caused by the cross-section reduction due to the problems associated with the use of steel plates, such as in welding, increased weight, thermal stress around the welding location, and the possibility of creating another deficiency by welding.

Key Words
Square Hollow Section (SHS); deficiency; CFRP; steel column; strengthening; steel plate

Address
Mehdi Shahraki, Mohammad Reza Sohrabi and Gholam Reza Azizyan: Department of Civil Engineering, University of Sistan and Baluchestan, Zahedan, Iran
Kambiz Narmashiri: Department of Civil Engineering, Zahedan Branch, Islamic Azad University, Zahedan, Iran


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