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CONTENTS
Volume 38, Number 5, March10 2021
 


Abstract
The main objective of this paper is to study vibration of sandwich open cylindrical panel with damaged core and FG face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions. It is seen that for the large amount of power-law index "P", increasing this parameter does not have significant effect on the non-dimensional natural frequency parameters of the FG sandwich curved panel. Results indicate that by increasing the value of isotropic damage parameter "D" up to the unity (fully damaged core) the frequency would tend to become zero. One can dictate the fiber variation profile through the radial direction of the sandwich panel via the amount of "P", "b" and "c" parameters. It should be noticed that with increase of volume fraction of fibers, the frequency parameter of the panels does not increase necessarily, so by considering suitable amounts of power-law index "P" and the parameters "b" and "c", one can get dynamic characteristics similar or better than the isotropic limit case for laminated FG curved panels.

Key Words
2-D differential quadrature method; damaged isotropic core; laminated curved panels; three-dimensional theory of elasticity; Halpin-Tsai equation; Eshelby-Mori-Tanaka scheme

Address
Li-Cai Zhao: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, No.43,
Sec.4, Keelung Road, Taipei 106, Taiwan;
China Railway 19th Bureau Co., Ltd, Beijing, 100176, China
Shi-Shuenn Chen: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, No.43,
Sec.4, Keelung Road, Taipei 106, Taiwan
Yi-Peng Xu: China Railway 19th Bureau Co., Ltd, Beijing, 100176, China;
School of Mathematics and Science, Tiangong University, Tianjin, 300387, China
Vahid Tahouneh: Young Researchers and Elite Club, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

Abstract
In this study, an effective numerical method is introduced for nonlinear inelastic analyses of rectangular concrete-filled steel tubular (CFST) frames for the first time. A steel-concrete composite fiber beam-column element model is developed that considers material, and geometric nonlinearities, and residual stresses. This is achieved by using stability functions combined with integration points along the element length to capture the spread of plasticity over the composite cross-section along the element length. Additionally, a multi-spring element with a zero-length is employed to model the nonlinear semi-rigid beam-to-column connections in CFST frame models. To solve the nonlinear equilibrium equations, the generalized displacement control algorithm is adopted. The accuracy of the proposed method is firstly verified by a large number of experiments of CFST members subjected to various loading conditions. Subsequently, the proposed method is applied to investigate the nonlinear inelastic behavior of rectangular CFST frames with fully rigid, semi-rigid, and hinged connections. The accuracy of the predicted results and the efficiency pertaining to the computation time of the proposed method are demonstrated in comparison with the ABAQUS software. The proposed numerical method may be efficiently utilized in practical designs for advanced analysis of the rectangular CFST structures.

Key Words
nonlinear analysis; fiber beam-column element; concrete-filled steel tubes; stability function; semi-rigid connections

Address
Van-Tuong Bui and Seung-Eock Kim: Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul, 05006, South Korea
Quang-Viet Vu: Institute of Research and Development, Duy Tan University, Danang 550000, Viet Nam
Viet-Hung Truong: Department of Civil Engineering, Thuyloi University, 175 Tay Son, Dong Da, Ha Noi, Viet Nam

Abstract
The generalized thermoelastic analysis problem of a two-dimension porous medium with and without energy dissipation are obtained in the context of Green–Naghdi's (GNIII) model. The exact solutions are presented to obtain the studying fields due to the pulse heat flux that decay exponentially in the surface of porous media. By using Laplace and Fourier transform with the eigenvalues scheme, the physical quantities are analytically presented. The surface is shocked by thermal (pulse heat flux problems) and applying the traction free on its outer surfaces (mechanical boundary) through transport (diffusion) process of temperature to observe the analytical complete expression of the main physical fields. The change in volume fraction field, the variations of the displacement components, temperature and the components of stress are graphically presented. Suitable discussion and conclusions are presented.

Key Words
Porous medium; fourier and laplace transform; eigenvalue approach; Green–Naghdi (GNIII) theory

Address
Faris Alzahrani: Nonlinear Analysis and Applied Mathematics Research Group (NAAM), Mathematics Department,
King Abdulaziz University, Jeddah, Saudi Arabia
Ibrahim A. Abbas: Nonlinear Analysis and Applied Mathematics Research Group (NAAM), Mathematics Department,
King Abdulaziz University, Jeddah, Saudi Arabia;
Department of Mathematics, Faculty of Science, Sohag University, Sohag, Egypt

Abstract
What is desirable in engineering is to bring the engineering model as close to reality as possible while the simplicity of model is also considered. In recent years, several studies have been performed on nanocomposites but some of these studies are somewhat far from reality. For example, in many of these studies, the carbon nanotubes (CNTs) are assumed completely straight, flawless and uniformly distributed throughout the matrix but by studying nanocomposites, we find that this is not the case. In this paper, three steps have been taken to bring the presented models for nanocomposites closer to reality. One is that assuming the straightness of nanotubes is removed and the waviness is considered. Also, the nanotubes are not considered to be pristine and the influence of defect is included in accordance with reality. In addition, the approximation of uniform distribution of nanotubes is ignored and according to experimental observations, the effect of nanotube aggregation is considered. As far as we know, this is the first study on these three topics together in an article. Moreover, we also include the size effects in our models for nanocomposites. To show the accuracy of our models, our results are calibrated with experimental results and compared with theoretical model. For numerical examples, we present the buckling behaviors of nanocomposites including the size effects using nonlocal theory and compare the results of our models with the results of models with above-mentioned approximations.

Key Words
wavy CNT; defected CNT; aggregated CNT; nanocomposite reinforced with CNTs; size effects

Address
Farshad Heidari, Keivan Taheri and aziar Janghorban: Department of Mechanical Engineering, Shiraz Branch, Islamic Azad University, Shiraz, Iran
Mehrdad Sheybani: Department of Mechanical Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran
Abdelouahed Tounsi: YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea

Abstract
This paper aims to explore the mechanical behavior and moment-rotation model of blind bolted joints between concrete-filled double skin steel tubular columns and steel-concrete composite beams. For this type of joint, the inner tube and sandwiched concrete were additionally identified as basic components compared with CFST blind bolted joint. A modified moment-rotation model for this type of connection was developed, of which the compatibility condition and mechanical equilibrium were employed to determine the internal forces of basic components and neutral axis. Following this, load transfer mechanism among the inner tube, sandwiched concrete and outer tube was discussed to assert the action area of the components. Subsequently, assembly processes of basic coefficients in terms of their stiffness and resistances based on the component method by simplifying them as assemblages of springs in series or in parallel. Finally, an experimental investigation on four substructure joints with CFDST columns for validation purposes was carried out to capture the connection details. The predicted results derived from the mechanical models coincided well with the experimental results. It is demonstrated that the proposed mechanical model is capable of evaluating the complete moment-rotation relationships of blind bolted CFDST column composite connections.

Key Words
component method; Moment-rotation model; concrete-filled double skin steel tubular (CFDST); blind bolt; composite joint

Address
Lei Guo, Wanqian Wang and Zhaodong Ding: School of Civil Engineering, Hefei University of Technology, Tunxi Road 193, Anhui Province, 230009, China
Jingfeng Wang: School of Civil Engineering, Hefei University of Technology, Tunxi Road 193, Anhui Province, 230009, China;
Anhui Civil Engineering Structures and Materials Laboratory, Tunxi Road 193, Anhui Province, 230009, China

Abstract
The present study experimentally and analytically investigated the push-out behaviour of H-shaped steel section embedded in ultrahigh-performance fibre-reinforced concrete (UHPFRC). The effect of significant parameters such as the concrete types, fibre content, embedded steel length, transverse reinforcement ratio and concrete cover on the bond stress, development of bond stress along the embedded length and failure mechanism has been reported. The test results show that the bond slip behaviour of steel-UHPFRC is different from the bond slip behaviour of steel-normal concrete and steel-high strength concrete. The bond-slip curves of steel-normal concrete and steel-high strength concrete exhibit brittle behaviour, and the bond strength decreases rapidly after reaching the peak load, with a residual bond strength of approximately one-half of the peak bond strength. The bond-slip curves of steel-UHPFRC show an obvious ductility, which exhibits a unique displacement pseudoplastic effect. The residual bond strength can still reach from 80% to 90% of the peak bond strength. Compared to steel-normal concrete, the transverse confinement of stirrups has a limited effect on the bond strength in the steel-UHPFRC substrate, but a higher stirrup ratio can improve cracking resistance. The experimental campaign quantifies the local bond stress development and finds that the strain distribution in steel follows an exponential rule along the steel embedded length. Based on the theory of mean bond and local bond stress, the present study proposes empirical approaches to predict the ultimate and residual bond resistance with satisfactory precision. The research findings serve to explain the interface bond mechanism between UHPFRC and steel, which is significant for the design of steel-UHPFRC composite structures and verify the feasibility of eliminating longitudinal rebars and stirrups by using UHPFRC in composite columns.

Key Words
bond slip; shear stress slip; concrete-encased column; ultrahigh-performance fibre reinforced concrete (UHPFRC); steel-concrete composite

Address
Zhenyu Huang, Weiwen Li, Chufa Chen, Yongjie Li, Zhiwei Lin: Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering,
Shenzhen University, Shenzhen 518060, P.R. China
Xinxiong Huang: Guangdong Provincial Key Laboratory of Durability for Marine Civil Engineering,
Shenzhen University, Shenzhen 518060, P.R. China;
Guangzhou Expressway Co., Ltd, Guangzhou Communications Investment Group co., Ltd, Guangzhou 510288, P.R. China
Wen-I Liao: Department of Civil Engineering, National Taipei University of Technology, Taipei 10608, Taiwan, P.R. China

Abstract
This article develops a nonclassical model to analyze bending response of squared perforated microbeams considering the coupled effect of microstructure and surface stress under different loading and boundary conditions, those are not be studied before. The corresponding material and geometrical characteristics of regularly squared perforated beams relative to fully filled beam are obtained analytically. The modified couple stress and the modified Gurtin-Murdoch surface elasticity models are adopted to incorporate the microstructure as well as the surface energy effects. The differential equations of equilibrium including the Poisson's effect are derived based on minimum potential energy. Exact closed form solution is obtained for bending behavior of the proposed model considering the classical and nonclassical boundary conditions for both uniformly distributed and concentrated loads. The proposed model is verified with results available in the literature. Influences of the microstructure length scale parameter, surface energy, beam thickness, boundary and loading conditions on the bending behavior of perforated microbeams are investigated. It is observed that microstructure and surface parameters are vital in investigation of the bending behavior of perforated microbeams. The obtained results are supportive for the design, analysis and manufacturing of perforated nanobeams that commonly used in nanoactuators, nanoswitches, MEMS and NEMS systems.

Key Words
equivalent geometrical model; microstructure and surface effects; perforated beam; bending behavior; classical and nonclassical boundary conditions; exact closed form

Address
Mashhour A. Alazwari: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia
Alaa A. Abdelrahman and Ahmed Wagih: Mechanical Design & Production Dept., Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt
Mohamed A. Eltaher: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia;
Mechanical Design & Production Dept., Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt
Hanaa E. Abd-El-Mottaleb: Structural Engineering Department, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt


Abstract
The ultimate strength behaviour of sandwich composite beams with J-hooks and normal weight concrete (SCSSBJNs) are studied through two-point loading tests on ten full-scale SCSSBJNs. The test results show that the SCSSBJN with different parameters under two-point loads exhibits three types of failure modes, i.e., flexure, shear, and combined shear and flexure mode. SCSSBJN failed in different failure modes exhibits different load-deflection behaviours, and the main difference of these three types of behaviours exist in their last working stages. The influences of thickness of steel faceplate, shear span ratio, concrete core strength, and spacing of J-hooks on structural behaviours of SCSSBJN are discussed and analysed. These test results show that the failure mode of SCSSBJN was sensitive to the thickness of steel faceplate, shear span ratio, and concrete core strength. Theoretical models are developed to estimate the cracking, yielding, and ultimate bending resistance of SCSSBJN as well as its transverse cross-sectional shear resistance. The validations of predictions by these theoretical models proved that they are capable of estimating strengths of novel SCSSBJNs.

Key Words
sandwich structures; bending tests; composite structures; J-hook connectors; theoretical models; ultimate strength behaviour; normal weight concrete; steel-concrete-steel

Address
Jia-Bao Yan: School of Civil Engineering / Key Laboratory of Coast Civil Structure Safety of Ministry of Education,
Tianjin University, Tianjin 300350, China
Xin Dong: School of Civil Engineering / Key Laboratory of Coast Civil Structure Safety of Ministry of Education,
Tianjin University, Tianjin 300350, China;
East China Architectural Design & Research Institute Company Limited, Shanghai 200002, China
Tao Wang: Key Laboratory of Earthquake Engineering and Engineering Vibration, Institute of Engineering Mechanics,
CEA, Harbin 150080, China



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