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CONTENTS
Volume 26, Number 1, July 2020
 

Abstract
In this paper, a procedure for automated optimized design of reinforced concrete frames has been presented. The procedure consists of formulation and solution of the design problem in the form of an optimization problem. The minimization of total cost of R/C frame has been taken as the objective of optimization problem. In this research, consistent approximation method is applied to explicitly formulate constraints and objective function in terms of the design variables. In the presented method, the primary optimization problem is replaced with a sequence of explicit sub-problems. Each sub-problem is efficiently solved using the Sequential Quadratic Programming (SQP) method. The proposed method is demonstrated through a four-story frame and an eight-story frame, and the optimum results are compared with those in the available literature. It is shown that the proposed method can be easily applied to obtain rational, reliable, economical and practical designs for Reinforced Concrete Moment Resisting Frames (RCMRFs) while it is converged after a few analyses.

Key Words
structural optimization; consistent approximation; sensitivity analysis; reinforced concrete frame

Address
Alireza Habibi: Department of Civil Engineering, Shahed University, Tehran, Iran
Mobin Shahryari and Hasan Rostami: Department of Civil Engineering, University of Kurdistan, Sanandaj, Iran

Abstract
Concrete are the most widely used manmade materials for infrastructure construction across the world. These constructions gradually aged and damaged due to long-term use. However, there does not exist an efficient concrete recycling method with low energy consumption. In this study, concrete was regarded as a heterogeneous material composed of coarse aggregate and cement mortar. And the failure mode of concrete under ultrasonic dynamic loading was investigated by finite element (FE) analysis. Simultaneously, a 3D random aggregate concrete model was programmed by APDL and imported into ABAQUS software, and the damage plastic constitutive model was applied to each phase to study the damage law of concrete under dynamic loading. Meanwhile, the dynamic damage process of concrete was numerically simulated, which observed ultrasonic propagating and the concrete crushing behavior. Finally, the FE simulation considering the influence of different aggregate volume and aggregate size was carried out to illustrate the damage level of concrete.

Key Words
concrete; ultrasonic; random aggregate model; damage plastic; numerical simulation

Address
Lixiao Wang: School of Mechanical Engineering, Changshu Institution of Technology, Changshu, 215500, China; School of Mechanics, Soochow University, Suzhou, 215000, China
Qidong Chen, Xin Liu, Bin Zhang: 1School of Mechanical Engineering, Changshu Institution of Technology, Changshu, 215500, China
Yichen Shen: School of Mechanics, Soochow University, Suzhou, 215000, China

Abstract
Buckling and post-buckling behaviors of geometrically imperfect annular sector plates made from nanoparticle reinforced composites have been investigated. Two types of nanoparticles are considered including graphene oxide powders (GOPs) and silicone oxide (SiO2). Nanoparticles are considered to have uniform and functionally graded distributions within the matrix and the material properties are derived using Halpin-Tsai procedure. Annular sector plate is formulated based upon thin shell theory considering geometric nonlinearity and imperfectness. After solving the governing equations via Galerkin\'s technique, it is showed that the post-buckling curves of annular sector plates rely on the geometric imperfection, nanoparticle type, amount of nanoparticles, sector inner/outer radius and sector open angle.

Key Words
post-buckling; thin shell theory; nanoparticles; graphene oxide powder; nonlinear stability

Address
Seyed Sajad Mirjavadi: Department of Mechanical and Industrial Engineering, Qatar University, P.O. Box 2713, Doha, Qatar
Masoud Forsat: Department of Mechanical and Industrial Engineering, Qatar University, P.O. Box 2713, Doha, Qatar
Saeed Mollaee: Auckland Bioengineering Institute, the University of Auckland, Auckland, New Zealand
Mohammad Reza Barati: Fidar Project Qaem Company, Darvazeh Dolat, Tehran, Iran
Behzad Mohasel Afshari: School of Mechanical Engineering, College of Engineering, Sharif University of Technology, Tehran, Iran
A.M.S. Hamouda: Department of Mechanical and Industrial Engineering, Qatar University, P.O. Box 2713, Doha, Qatar

Abstract
This paper investigates the size dependent effect on the vibration analysis of a porous nanocomposite viscoelastic plate reinforced by functionally graded-single walled carbon nanotubes (FG-SWCNTs) by considering nonlocal strain gradient theory. Therefore, using energy method and Hamilton\'s principle, the equations of motion are derived. In this article, the effects of nonlocal parameter, aspect ratio, strain gradient parameter, volume fraction of carbon nanotubes (CNTs), damping coefficient, porosity coefficient, and temperature change on the natural frequency are perused. The innovation of this paper is to compare the effectiveness of each mentioned parameters individually on the free vibrations of this plate and to represent the appropriate value for each parameter to achieve an ideal nanocomposite plate that minimizes vibration. The results are verified with those referenced in the paper. The results illustrate that the effect of damping coefficient on the increase of natural frequency is significantly higher than the other parameters effect, and the effects of the strain gradient parameter and nonlocal parameter on the natural frequency increase are less than damping coefficient effect, respectively. Furthermore, the results indicate that the natural frequency decreases with a rise in the nonlocal parameter, aspect ratio and temperature change. Also, the natural frequency increases with a rise in the strain gradient parameter and CNTs volume fraction. This study can be used for optimizing the industrial and medical designs, such as automotive industry, aerospace engineering and water purification system, by considering ideal properties for the nanocomposite plate.

Key Words
vibration analysis; porous materials; nanocomposite; carbon nanotube; nonlocal strain gradient theory; Hamilton

Address
Pegah Khazaei and Mehdi Mohammadimehr: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran

Abstract
Concrete is the most widely used substance in construction industry, so it\'s been required to improve its quality using new technologies. Nowadays, nanotechnology offers new frontiers for improving construction materials. In this paper, we study the stability analysis of the Single Walled Carbon Nanotubes (SWCNT) reinforced concrete cylindrical shell embedded in elastic foundation using the Donnell cylindrical shell theory. In this regard, we propose a new explicit analytical formula of the critical buckling load which takes into account the distribution of SWCNT reinforcement through the thickness of the concrete shell using the U, X, O and V forms and the elastic foundation using Winkler and Pasternak models. The rule of mixture is used to calculate the effective properties of the reinforced concrete cylindrical shell. The influence of diverse parameters on the stability behavior of the reinforced concrete shell is also discussed.

Key Words
stability analysis; SWCNT reinforced concrete cylindrical shell; elastic foundation; donnell shell theory

Address
Abdelaziz Timesli: National Higher School of Arts and Crafts of Casablanca (ENSAM Casablanca), Laboratory of Structural Engineering, Intelligent Systems and Electrical Energy, Hassan II University of Casablanca, 150 Avenue Nile Sidi Othman, 20670, Casablanca, Morocco; National School of Applied Sciences of Al-Hoceima (ENSA d\'iAl-Hoceima), Applied Sciences Laboratory, Abdelmalek Essaadi University,
BP 03, Ajdir, Al-Hoceima, Morocco

Abstract
In this investigation, study of the bending response of functionally graded (FG) porous plates is presented using a cubic shear deformation theory. The properties of the FG-plate vary according to a power-law distribution which is modified to approximate material characteristics for considering the effect of porosities. The equilibrium equations are derived by using the principle of virtual work and solved by using Navier\'s procedure. Various numerical results are discussed to demonstrate the influence of the variation of the power index, the porosity parameter and the geometric ratios on the bending response of FG porous plates.

Key Words
functionally graded plate; porosity; bending; shear deformation theory

Address
Abdallah Zine: Faculty of Technology, Civil Engineering Department, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria; Centre Universitaire de Relizane, Algerie
Abdelmoumen Anis Bousahla: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
Fouad Bourada: Faculty of Technology, Civil Engineering Department, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia; Departement des Sciences et de la Technologie, Centre Universitaire de Tissemsilt, BP 38004 Ben Hamouda, Algerie
Kouider Halim Benrahou: Faculty of Technology, Civil Engineering Department, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
Abdeldjebbar Tounsi: Faculty of Technology, Civil Engineering Department, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
E.A. Adda Bedia: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia
S.R. Mahmoud: GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia
Abdelouahed Tounsi: Faculty of Technology, Civil Engineering Department, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
The aim of this research is to investigate free vibration of a novel five layer Timoshenko microbeam which consists of a transversely flexible porous core made of Al-foam, two graphen platelets (GPL) nanocomposite reinforced layers to enhance the mechanical behavior of the structure as well as two piezo-magneto-electric face sheets layers. This microbeam is subjected to a thermal load and resting on Pasternak\'s foundation. To accomplish the analysis, constitutive equations of each layer are derived by means of nonlocal strain gradient theory (NSGT) to capture size dependent effects. Then, the Hamilton\'s principle is employed to obtain the equations of motion for five layer Timoshenko microbeam. They are subsequently solved analytically by applying Navier\'s method so that discretized governing equations are determined in form of dynamic matrix giving the possibility to gain the natural frequencies of the Timoshenko microbeam. Eventually, after a validation study, the numerical results are presented to study and discuss the influences of various parameters such as nonlocal parameter, strain gradient parameter, aspect ratio, porosity, various volume fraction and distributions of graphene platelets, temperature change and elastic foundation coefficients on natural frequencies of the sandwich microbeam.

Key Words
free vibration; five layers Timoshenko sandwich microbeam; transversely flexible porous core; GPL; piezomagneto- electric; nonlocal strain gradient theory

Address
Mehdi Mohammadimehr, Saeed Firouzeh, Mahsa Pahlavanzadeh,
Yaser Heidari and Mohsen Irani-Rahaghi: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Ghotbe Ravandi Blvd., Kashan, Iran

Abstract
Castellated beams fabricated from standard I-sections are being used for several structural applications such as commercial and industrial buildings, multistory buildings, warehouses and portal frames in view of numerous advantages. The advantages include enhanced moment of inertia, stiffness, flexural resistance, reduction in weight of structure, by passing the used plate girders, the passage of service through the web openings etc. In the present study, experimental and numerical investigations were carried out on concrete encased steel castellated beams with hexagonal openings under flexural loading. Various positions of openings such as along the neutral axis, above the neutral axis and below the neutral axis were considered for the study. From the experimental findings, it has been observed that the load-carrying capacity of the castellated beam with web opening above neutral axis is found to be higher compared to other configurations. Nonlinear finite element analysis was performed by using general purpose finite element software ABAQUS considering the material nonlinearities. Concrete damage plasticity model was employed to model the nonlinearity of concrete and elasto-plastic model for steel. It has been observed that FE model could able to capture the behaviour of concrete encased steel castellated beams and the predicted values are in good agreement with the corresponding experimental values.

Key Words
concrete; steel; castellated beam; flexural behavior; concrete damage model; finite element analysis

Address
G. Velrajkumar: Department of Civil Engineering, SVS College of Engineering, Coimbatore, Tamil Nadu, 642 109, India
M.P. Muthuraj: Department of Civil Engineering, Coimbatore Institute of Technology, Coimbatore, Tamil Nadu,641 014, India

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