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CONTENTS
Volume 34, Number 2, January25 2020
 

Abstract
The past research on cold-formed steel (CFS) flexural members have proved that rectangular hollow flanged sections perform better than conventional I-sections due to their higher torsional rigidity over the later ones. However, CFS members are vulnerable to local buckling, substantially due to their thin-walled features. The use of packing, such as firmly connected timber planks, to the flanges of conventional CFS lipped I-sections can drastically improve their flexural performance as well as structural efficiency. Whilst several CFS composites have been developed so far, only limited packing materials have been tried. This paper presents a series of tests carried out on different rectangular hollow compression flanged sections with innovative packing materials. Four-point flexural tests were carried out to assess the flexural capacity, failure modes and deformed shapes of the CFS composite beam specimens. The geometric imperfections were measured and reported. The North American Specifications and Indian Standard for cold-formed steel structures were used to compare the design strengths of the experimental specimen. The test results indicate clearly that CFS rectangular \'compression\' flanged composite beams perform significantly better than the conventional rectangular hollow flanged CFS sections.

Key Words
cold-formed steel; composite sections; experiment; flexural members; local buckling

Address
M. Adil Dar: Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi, India
N. Subramanian: Consulting Engineer, Maryland, USA
Dawood A. Dar snd A.R. Dar: Department of Civil Engineering, National Institute of Technology Srinagar, J&K, India
M. Anbarasu: Department of Civil Engineering, Government College of Engineering Salem, Tamilnadu, India
James B. P. Lim: Department of Civil & Environmental Engineering, University of Auckland, New Zealand
Soroush Mahjoubi: School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran

Abstract
Stainless-clad (SC) bimetallic steels that are manufactured by metallurgically bonding stainless steels as cladding metal and conventional mild steels as substrate metal, are kind of advanced steel plate products. Such advanced composite steels are gaining increasingly widespread usage in a range of engineering structures and have great potential to be used extensively for large civil and building infrastructures. Unfortunately, research work on the SC bimetallic steels from material level to structural design level for the applications in structural engineering field is very limited. Therefore, the aim of this paper is to investigate the material behaviour of the SC bimetallic steels under the cyclic loading which structural steels usually could encounter in seismic scenario. A number of SC bimetallic steel coupon specimens are tested under monotonic and cyclic loadings. The experimental monotonic and cyclic stress-strain curves of the SC bimetallic steels are obtained and analysed. The effects of the clad ratio that is defined as the ratio of the thickness of cladding layer to the total thickness of SC bimetallic steel plate on the monotonic and cyclic behaviour of the SC bimetallic steels are studied. Based on the experimental observations, a cyclic constitutive model with combined hardening criterion is recommended for numerical simulation of the cyclic behaviour of the SC bimetallic steels. The parameters of the constitutive model for the SC bimetallic steels with various clad ratios are calibrated. The research outcome presented in this paper may provide essential reference for further seismic analysis of structures fabricated from the SC bimetallic steels.

Key Words
bimetallic steels; stainless-clad; monotonic; cyclic; constitutive model; clad ratio

Address
Xinpei Liu and Brian Uy: School of Civil Engineering, Faculty of Engineering, The University of Sydney, NSW, 2006, Australia
Huiyong Ban: Key Laboratory of Civil Engineering Safety and Durability of China Education Ministry,
Department of Civil Engineering, Tsinghua University, China
Juncheng Zhu: School of Civil Engineering, Beijing Jiaotong University, Beijing, China


Abstract
The aim of this study is to investigate free vibration of functionally graded porous nanocomposite rectangular plates where the internal pores and graphene platelets (GPLs) are distributed in the matrix either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. The GPL-reinforced plate is modeled using a semi-analytic approach composed of generalized differential quadrature method (GDQM) and series solution adopted to solve the equations of motion. The proposed rectangular plates have two opposite edges simply supported, while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. The 2-D differential quadrature method as an efficient and accurate numerical tool is used to discretize the governing equations and to implement the boundary conditions. The convergence of the method is demonstrated and to validate the results, comparisons are made between the present results and those reported by well-known references for special cases treated before, have confirmed accuracy and efficiency of the present approach. New results reveal the importance of porosity coefficient, porosity distribution, graphene platelets (GPLs) distribution, geometrical and boundary conditions on vibration behavior of porous nanocomposite plates. It is observed that the maximum vibration frequency obtained in the case of symmetric porosity and GPL distribution, while the minimum vibration frequency is obtained using uniform porosity distribution.

Key Words
porous nanocomposite plates; generalized differential quadrature method (GDQM); Halpin-Tsai micromechanics model; Vibration analysis

Address
Changlin Zhou, Zhongxian Zhang and Ji Zhang: School of Civil Engineering and Mechanics, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China
Yuan Fang: General Construction Company of CCTEB Group Co., Wuhan, Hubei, 430064, China
Vahid Tahouneh: Young Researchers and Elite Club, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

Abstract
The aim of this study is to obtain the nonlinear and post-buckling responses of relatively thick functionally graded plates with oblique elliptical cutouts using a new semi-analytical approach. To model the oblique elliptical hole in a FGM plate, six plate-elements are used and the connection between these elements is provided by the well-known Penalty method. Therefore, the semi-analytical technique used in this paper is known as the plate assembly technique. In order to take into account for functionality of the material in a perforated plate, the volume fraction of the material constituents follows a simple power law distribution. Since the FGM perforated plates are relatively thick in this research, the structural model is assumed to be the first order shear deformation theory and Von-Karman\'s assumptions are used to incorporate geometric nonlinearity. The equilibrium equations for FGM plates containing elliptical holes are obtained by the principle of minimum of total potential energy. The obtained nonlinear equilibrium equations are solved numerically using the quadratic extrapolation technique. Various sets of boundary conditions for FGM plates and different cutout sizes and orientations are assumed here and their effects on nonlinear response of plates under compressive loads are examined.

Key Words
post-buckling behavior; oblique elliptical cutouts; functionally graded plates; plate assembly technique; penalty method, Mapping

Address
S.A.M. Ghannadpour and M. Mehrparvar: New Technologies and Engineering Department, Shahid Beheshti University, G.C, Tehran, Iran

Abstract
This article presented a comprehensive model to study static buckling stability and associated mode-shapes of higher shear deformation theories of sandwich laminated composite beam under the compression of varying axial load function. Four higher order shear deformation beam theories are considered in formulation and analysis. So, the model can consider the influence of both thick and thin beams without needing to shear correction factor. The compression force can be described through axial direction by uniform constant, linear and parabolic distribution functions. The Hamilton\'s principle is exploited to derive equilibrium governing equations of unified sandwich laminated beams. The governing equilibrium differential equations are transformed to algebraic system of equations by using numerical differential quadrature method (DQM). The system of equations is solved as an eigenvalue problem to get critical buckling loads and their corresponding mode-shapes. The stability of DQM in determining of buckling loads of sandwich structure is performed. The validation studies are achieved and the obtained results are matched with those. Parametric studies are presented to figure out effects of in-plane load type, sandwich thickness, fiber orientation and boundary conditions on buckling loads and mode-shapes. The present model is important in designing process of aircraft, naval structural components, and naval structural when non-uniform in-plane compressive loading is dominated.

Key Words
sandwich composite; buckling stability; mode-shapes; varying axial load; unified beam theories; Differential Quadrature Method (DQM); convergence of DQM

Address
Mohamed A. Eltaher: Department of Mechanical Engineering, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia;
Department of Mechanical Design & Production, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt
Salwa A Mohamed: Department of Engineering Mathematics, Faculty of Engineering, Zagazig University, P.O. Box 44519, Zagazig, Egypt


Abstract
The main objective of this research paper is to consider vibration analysis of vacancy defected graphene sheet as a nonisotropic structure via molecular dynamic and continuum approaches. The influence of structural defects on the vibration of graphene sheets is considered by applying the mechanical properties of defected graphene sheets. Molecular dynamic simulations have been performed to estimate the mechanical properties of graphene as a nonisotropic structure with single- and double- vacancy defects using open source well-known software i.e., large-scale atomic/molecular massively parallel simulator (LAMMPS). The interactions between the carbon atoms are modelled using Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential. An isogeometric analysis (IGA) based upon non-uniform rational B-spline (NURBS) is employed for approximation of single-layered graphene sheets deflection field and the governing equations are derived using nonlocal elasticity theory. The dependence of small-scale effects, chirality and different defect types on vibrational characteristic of graphene sheets is investigated in this comprehensive research work. In addition, numerical results are validated and compared with those achieved using other analysis, where an excellent agreement is found. The interesting results indicate that increasing the number of missing atoms can lead to decrease the natural frequencies of graphene sheets. It is seen that the degree of the detrimental effects differ with defect type. The Young\'s and shear modulus of the graphene with SV defects are much smaller than graphene with DV defects. It is also observed that Single Vacancy (SV) clusters cause more reduction in the natural frequencies of SLGS than Double Vacancy (DV) clusters. The effectiveness and the accuracy of the present IGA approach have been demonstrated and it is shown that the IGA is efficient, robust and accurate in terms of nanoplate problems.

Key Words
defected graphene; vibration analysis; isogeometric method; NURBS; nonlocal elasticity theory; molecular dynamic

Address
Vahid Tahouneh, Mohammad Hasan Naei and Mahmoud Mosavi Mashhadi: School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran

Abstract
The computational post-buckling strength of the tilted sandwich composite shell structure is evaluated in this article. The computational responses are obtained using a mathematical model derived using the higher-order type of polynomial kinematic in association with the through-thickness stretching effect. Also, the sandwich deformation behaviour of the flexible soft-core sandwich structural model is expressed mathematically with the help of a generic nonlinear strain theory i.e. Green-Lagrange type strain-displacement relations. Subsequently, the model includes all of the nonlinear strain terms to account the actual deformation and discretized via displacement type of finite element. Further, the computer code is prepared (MATLAB environment) using the derived higher-order formulation in association with the direct iterative technique for the computation of temperature carrying capacity of the soft-core sandwich within the post-buckled regime. Further, the nonlinear finite element model has been tested to show its accuracy by solving a few numerical experimentations as same as the published example including the consistency behaviour. Lastly, the derived model is utilized to find the temperature load-carrying capacity under the influences of variable factors affecting the soft-core type sandwich structural design in the small (finite) strain and large deformation regime including the effect of tilt angle.

Key Words
post-buckling; sandwich; skew; HSDT; thermal loading; FEM

Address
Pankaj V. Katariya and Subrata Kumar Panda: Department of Mechanical Engineering, National Institute of Technology Rourkela, Odisha, India

Abstract
In the present research post-buckling of a cut out plate reinforced through carbon nanotubes (CNTs) resting on an elastic foundation is studied. Material characteristics of CNTs are hypothesized to be altered within thickness orientation which are calculated according to Mori-Tanaka model. For modeling the system mathematically, first order shear deformation theory (FSDT) is applied and using energy procedure, the governing equations can be derived. With respect to Rayleigh-Ritz procedure as well as Newton-Raphson iterative scheme, the motion equations are solved and therefore, post-buckling behavior of structure will be tracked. Diverse parameters as well as their reactions on post-buckling paths focusing cut out measurement, CNT\'s volume fraction and agglomeration, dimension of plate and an elastic foundation are investigated. It is revealed that presence of a square cut out can affect negatively post-buckling behavior of structure. Moreover, adding nanocompsits in the matrix leads to enhancement of post-buckling response of system.

Key Words
post-buckling; rectangular cut out plate; FSDT; Newton-Raphson iterative technique; nanocomposite

Address
Mohsen Motezaker: School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran
Arameh Eyvazian: Mechanical and Industrial Engineering Department, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar

Abstract
This study aims to carry out the experimental and numerical investigation on the flexural behavior of sandwich honeycomb composite (SHC) beams reinforced with novel triaxially woven fabric composite skins. Different stacking sequences of the carbon fiber reinforcement polymer (CFRP) laminate; i.e., 0-direction of TW (TW0), 0-direction of TW (TW0), 0-direction of UD (UD0), and 90-direction of UD (UD90) were studied, from which the flexural behavior of SHC beam behaviors reinforced with TW0/UD0 or TW0/UD90 novel laminated skins were compared with those reinforced with UD0/90 conventional laminated skins under four-point loading. Generally, TW0/UD0 SHC beams displayed the same flexural stiffness as UD0/90 SHC beams in terms of load-deflection relationships. In contrast, TW0/UD90 SHC beams showed a 70% lower efficiency than those of UD0/90 SHC. Hence, the TW0/UD0 laminate arrangement is more effective with a mass reduction of 39% compared with UD0/90 for SHC beams, although their stiffness and shear strength are practically identical.

Key Words
flexural behavior; sandwich honeycomb composite; carbon fiber reinforced polymer; unidirectional; triaxial woven fabric

Address
M.Y. Al-Fasih and M.H.W. Ibrahim: Jamilus Research Centre, Faculty of Civil Engineering and Built Environment,
Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Johor, Malaysia
A.B.H. Kueh : Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia


Abstract
The objective is to study the deformation in a homogeneous isotropic modified couple stress thermoelastic medium with mass diffusion and with two temperatures due to a thermal source and mechanical force. Laplace and Fourier transform techniques are applied to obtain the solutions of the governing equations. The displacements, stress components, conductive temperature, mass concentration and couple stress are obtained in the transformed domain. Numerical inversion technique has been used to obtain the solutions in the physical domain. Isothermal boundary and insulated boundaryconditions are used to investigate the problem. Some special cases of interest are also deduced.

Key Words
isotropic solid; two temperatures; Laplace and Fourier transforms; mass concentration; modified couple stress; thermoelastic; mass diffusion

Address
Harpreet Kaur and Parveen Lata: Department of Basic and Applied Sciences, Punjabi University, Patiala, Punjab, India


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