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CONTENTS
Volume 25, Number 3, October30 2017
 

Abstract
In this article, an efficient and simple refined theory is proposed for buckling analysis of functionally graded plates by using a new displacement field which includes undetermined integral variables. This theory contains only four unknowns, with is even less than the first shear deformation theory (FSDT). Governing equations are obtained from the principle of virtual works. The closed-form solutions of rectangular plates are determined. Comparison studies are carried out to check the validity of obtained results. The influences of loading conditions and variations of power of functionally graded material, modulus ratio, aspect ratio, and thickness ratio on the critical buckling load of functionally graded plates are examined and discussed.

Key Words
bending analysis; functionally graded plate; plate theory

Address
Hichem Bellifa, Ahmed Bakora and Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Abdelmoumen Anis Bousahla: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, Université de Sidi Bel Abbes, Faculté de Technologie, Département de génie civil, Algeria;
Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes,
Département de Physique, Université de Sidi Bel Abbés, Algeria
S.R. Mahmoud: Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia

Abstract
The use of Hollow Structural Sections (HSS) provides an alternative for steel buildings in seismic zones, with the advantage over WF columns that the HSS columns have similar resistance along both axes and enhanced performance under flexure, compression and torsion with respect to other columns sections. The HSS columns have shown satisfactory performance under seismic loads, such as observed in buildings with steel moment frames in the Honshu earthquake (2011). The purpose of this research is to propose a new moment connection, EP-HSS (\"End-plate to Hollow Structural Section\"), using a wide flange beam and HSS column where the end plate falls outside the range of prequalification established in the ANSI/AISC 358-10 Specification, as an alternative to the traditional configuration of steel moment frames established in current codes. The connection was researched through analytical, numerical (FEM), and experimental studies. The results showed that the EP-HSS allowed the development of inelastic action on the beam only, avoiding stress concentrations in the column and developing significant energy dissipation. The experiments followed the qualification protocols established in the ANSI/AISC 341-10 Specification satisfying the required performance for highly ductile connections in seismic zones, thereby ensuring satisfactory performance under seismic actions without brittle failure mechanisms.

Key Words
ductility; performance; bolted connection; end-plate connection; hollow structural sections; moment connections; finite element method; steel structure; yield line; seismic design

Address
Eduardo Nuñez and Ricardo Herrera: Department of Civil Engineering, University of Chile, Av. Blanco Encalada 2002, Piso 4, 8370449 Santiago, Chile
Ronald Torres : Materials and Structural Models Institute, Faculty of Engineering, Universidad Central de Venezuela, Caracas, Venezuela

Abstract
The present study aims to determine the structural response of full scaled rectangular columns under both of vertical and lateral loads using numerical methods. In the study, the composite columns considering full concrete filled circular steel tube (FCFRST) and concrete filled double-skin rectangular steel tube (CFDSRST) section types are numerically modelled using ANSYS software. Vertical and lateral loads are applied to models to assess the structural response of the composite elements. Also similar investigations are done for reinforced concrete rectangular (RCR) columns to compare the results with those of composite elements. The analyses of the systems are statically performed for both linear and nonlinear materials. In linear static analyses, both of vertical and lateral loads are applied to models as only one step. However in nonlinear analyses, while vertical loads are applied to model as only one step, lateral loads are applied to systems as step by step. The displacement and stress changes in some critical nodes and sections and contour diagrams are reported by graphs and figures. At the end of the study, it is demonstrated that the nonlinear models reveal more accurate result then those of linear models. Also, it is highlighted that composite columns provide more and more safety, ductility compared to reinforced concrete column.

Key Words
omposite column; finite element modeling; linear and nonlinear analyses; structural response; vertical and lateral loads thermal buckling; sandwich plate; functionally graded materials; plate theory

Address
Baris Sevim: Yildiz Technical University, Department of Civil Engineering, 34220, İstanbul, Turkey

Abstract
The aim of this paper is to investigate the performance of Lightweight Aggregate Concrete Filled Steel Tube (LWCFST) columns experimentally and compare to the behavior of Self-Compacted Concrete Filled Steel Tube (SCCFST) columns under axial loading. Four different L/D ratios and three D/t ratios were used in the experimental program to delve into the compression behaviours. Compressive strength of the LWC and SCC are 33.47 MPa and 39.71 MPa, respectively. Compressive loading versus end shortening curves and the failure mode of sixteen specimens were compared and discussed. The design specification formulations of AIJ 2001, AISC 360-16, and EC4 were also assessed against test results to underline the performance of specification methods in predicting the compression capacity of LWCFST and SCCFST columns. Based on the behaviour of the SCCFST columns, LWCFST columns exhibited different performances, especially in ductility and failure mode. The nature of the utilized lightweight aggregate led to local buckling mode to be dominant in LWCFST columns, even the long LWCFST specimens suffered from this behaviour. While with the SCCFST specimens the global buckling governed the failure mode of long specimens without any loss in capacity. Considering a wide range of column geometries (short, medium and long columns), this paper extends the current knowledge in composite construction by examining the potential of two promising and innovative structural concrete types in CFST applications.

Key Words
lightweight aggregate concrete; self-compacted concrete; concrete filled steel tube column; design specifications

Address
Baraa J.M. AL-Eliwi: Department of Civil Engineering , University of Gaziantep, 27310 Gaziantep, Turkey;
Department of Civil Engineering, University of Mosul, 41001 Mosul, Iraq
Talha Ekmekyapar, Radhwan H. Faraj, M. and Tolga Göǧüş: Department of Civil Engineering, University of Gaziantep, 27310 Gaziantep, Turkey
A.M. AL-Shaar: Civil Engineering Department, University of Gaziantep, 27310 Gaziantep, Turkey;
Civil Engineering Department, Al-Nahrain University, 10072 Baghdad, Iraq



Abstract
In this work, thermoelastic dynamic behavior of functionally graded carbon nanotube reinforced composite (FG-CNTRC) cylinders subjected to mechanical pressure loads, uniform temperature environment or thermal gradient loads is investigated by a mesh-free method. The material properties and thermal stress wave propagation of the nanocomposite cylinders are derived after solving of the transient thermal equation and obtaining of the time history of temperature field of the cylinders. The nanocomposite cylinders are made of a polymer matrix and wavy single-walled carbon nanotubes (SWCNTs). The volume fraction of carbon nanotubes (CNTs) are assumed variable along the radial direction of the axisymmetric cylinder. Also, material properties of the polymer and CNT are assumed temperature-dependent and mechanical properties of the nanocomposite are estimated by a micro mechanical model in volume fraction form. In the mesh-free analysis, moving least squares shape functions are used to approximate temperature and displacement fields in the weak form of motion equation and transient thermal equation, respectively. Also, transformation method is used to impose their essential boundary conditions. Effects of waviness, volume fraction and distribution pattern of CNT, temperature of environment and direction of thermal gradient loads are investigated on the thermoelastic dynamic behavior of FG-CNTRC cylinders.

Key Words
thermoelastic dynamic analysis; thermal gradient loads; wavy carbon nanotubes; nanocomposite cylinders; mesh-free

Address
Rasool Moradi-Dastjerdi: Department of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr, Iran
Gholamhassan Payganeh: Department of Mechanical Engineering, Shahid Rajaee Teacher Training University (SRTTU), Tehran, Iran

Abstract
o gain more knowledge of aluminum foam sandwich structure and promote the engineering application, aluminum foam sandwich consisting of 7050 matrix aluminum foam core and 304 stainless steel face-sheets was studied under three-point bending by WDW-T100 electronic universal tensile testing machine in this work. Results showed that when aluminum foam core was reinforced by 304 steel face-sheets, its load carrying capacity improved dramatically. The maximum load of AFS in three-point bending increased with the foam core density or face-sheet thickness monotonically. And also when foam core was reinforced by 304 steel panels, the energy absorption ability of foam came into play effectively. There was a clear plastic platform in the load-displacement curve of AFS in three-point bending. No crack of 304 steel happened in the present tests. Two collapse modes appeared, mode A comprised plastic hinge formation at the mid-span of the sandwich beam, with shear yielding of the core. Mode B consisted of plastic hinge formation both at mid-span and at the outer supports.

Key Words
composite materials; three-point bending; mechanical properties; failure mechanism

Address
Chang Yan and Xuding Song:Key Laboratory of Road Construction Technology & Equipment of Chang\'an University, MOE, Xi\'an, Shaanxi 710064 China

Abstract
Sandwich shells made of composite materials are the main focus on recent literature parallel to the requirements of industry. They are commonly chosen for the modern engineering applications which require moderate strength to weight ratio without dependence on conventional manufacturing techniques. The investigations on hyperbolic paraboloidal formed sandwich composite shells are limited in the literature contrary to shells that have a number of studies, consisting of doubly curved surfaces, arbitrary boundaries and laminations. Because of the lack of contributive data in the literature, the aim of this study is to present the effects of curvature on hyperbolic paraboloidal formed, layered sandwich composite surfaces that have arbitrary boundary conditions. Analytical solution methodology for the analyses of stresses and deformations is based on Third Order Shear Deformation Theory (TSDT). Double Fourier series, which are specialized for boundary discontinuity, are used to solve highly coupled linear partial differential equations. Numerical solutions showing the effects of shell geometry are presented to provide benchmark results.

Key Words
sandwich composites; hyperbolic paraboloidal shell; boundary-discontinuity; fourier series

Address
Veysel Alankaya : Department of Naval Architecture, Turkish Naval Academy, Tuzla, 34942 Istanbul, Turkey
Cengiz Erdönmez: Department of Mathematics, Turkish Naval Academy, Tuzla, 34942 Istanbul, Turkey

Abstract
The goal of this study is to fill this apparent gap in the area about vibration analysis of multiwalled carbon nanotubes (MWCNTs) curved panels by providing 3-D vibration analysis results for functionally graded multiwalled carbon nanotubes (FG-MWCNTs) sandwich structure with power-law distribution of nanotube. The effective material properties of the FG-MWCNT structures are estimated using a modified Halpin-Tsai equation. Modified Halpin-Tsai equation was used to evaluate the Young\'s modulus of MWCNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin-Tsai equation from expressing a straight line to a nonlinear one in the MWCNTs wt% range considered. Also, the mass density and Poisson\'s ratio of the MWCNT/phenolic composite are considered based on the rule of mixtures. Parametric studies are carried out to highlight the influence of MWCNT volume fraction in the thickness, different types of CNT distribution, boundary conditions and geometrical parameters on vibrational behavior of FG-MWCNT thick curved panels. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary conditions including Free, Simply supported and Clamped at the curved edges. For an overall comprehension on 3-D vibration analysis of sandwich panel, some mode shape contour plots are reported in this research work.

Key Words
FG-MWCNT structures; vibration; thick laminated structures; three-dimensional theory of elasticity; Halpin-Tsai equation; mode shape analysis

Address
Vahid Tahouneh: Young Researchers and Elite Club, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

Abstract
In this study, the influences of triaxial magnetic field on the wave propagation behavior of anisotropic nanoplates are studied. In order to include small scale effects, nonlocal strain gradient theory has been implemented. To study the nanoplate as a continuum model, the three-dimensional elasticity theory is adopted in Cartesian coordinate. In our study, all the elastic constants are considered and assumed to be the functions of (x, y, z), so all kind of anisotropic structures such as hexagonal and trigonal materials can be modeled, too. Moreover, all types of functionally graded structures can be investigated. eigenvalue method is employed and analytical solutions for the wave propagation are obtained. To justify our methodology, our results for the wave propagation of isotropic nanoplates are compared with the results available in the literature and great agreement is achieved. Five different types of anisotropic structures are investigated in present paper and then the influences of wave number, material properties, nonlocal and gradient parameter and uniaxial, biaxial and triaxial magnetic field on the wave propagation analysis of anisotropic nanoplates are presented. From the best knowledge of authors, it is the first time that three-dimensional elasticity theory and nonlocal strain gradient theory are used together with no approximation to derive the governing equations. Moreover, up to now, the effects of triaxial magnetic field have not been studied with considering size effects in nanoplates. According to the lack of any common approximations in the displacement field or in elastic constant, present theory has the potential to be used as a bench mark for future works.

Key Words
triaxial magnetic field; anisotropic nanoplate; nonlocal strain gradient theory; three-dimensional elasticity theory

Address
Behrouz Karami and Maziar Janghorban: Department of Mechanical Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran
Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria

Abstract
This paper presents a combined experimental, numerical, and analytical study on elliptical concrete-filled steel tubular (E-CFT) and rebar-stiffened elliptical concrete-filled steel tubular (RE-CFT) subjected to axial loading. ABAQUS was used to establish 3D finite element (FE) models for the composite columns and the FE results agreed well with the experimental results. It was found that the ultimate load-bearing capacity of RE-CFT stub columns was 20% higher than that of the E-CFT stub columns. Such improvement was attributed to the reinforcement effects from the internal rebar-stiffeners, which effectively enhanced the confinement effect on the core concrete, thereby significantly improved both the ultimate bearing capacity and the ductility of the E-CFT columns. Based on the results, equations were also established in this paper to predict the bearing capacities of E-CFT and RE-CFT stub columns under axial loading. The predicted results agreed well with both experimental and numerical results, and had much higher accuracy than other available methods.

Key Words
rebar-stiffened; elliptical concrete-filled steel tubular (E-CFT); finite element analysis (FEA); Ultimate bearing capacity

Address
Fa-xing Ding, Xing-zhi Ding, Hai-bo Wang and Chang-jing Fang: School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P. R. China
Xue-mei Liu: Schoo of Civil Engineering and Built Environment, Queensland University of Technology,
Brisbane, QLD 4001, Australia
Xue-mei Liu: School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P. R. China;
National Engineering Laboratory for High Speed Railway Construction, Changsha 410075, China



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