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CONTENTS
Volume 34, Number 4, February25 2020
 

Abstract
Genetic Algorithm (GA) is a meta-heuristic algorithm which is capable of providing robust solutions for optimal design of structural components, particularly those one needs considering many design requirements. Hence, it has been successfully used by engineers in the typology optimization of structural members. As a novel approach, this study employs GA in order for conducting a case study with high constraints on the optimum mechanical properties of reinforced concrete (RC) beams under different load combinations. Accordingly, unified optimum sections through a computer program are adopted to solve the continuous beams problem. Genetic Algorithms proved in finding the optimum resolution smoothly and flawlessly particularly in case of handling many complicated constraints like a continuous beam subjected to different loads as moments shear - torsion regarding the curbs of design codes.

Key Words
reinforced concrete; optimum structures; genetic algorithms; optimization

Address
Enqiang Zhu and Zehui Shao: Institute of Computing Science and Technology, Guangzhou University, Guangzhou 510006, China
Rabi Muyad Najem: Department of civil engineering, MosulUniversity, Mosul, Iraq
Du Dinh-Cong:Division of Construction Computation, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam
Karzan Wakil: Research Center, Sulaimani Polytechnic University, Sulaimani 46001, Kurdistan Region, Iraq;
Research Center, Halabja University, Halabja 46018, Kurdistan Region, Iraq
Lanh Si Ho: Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam
Rayed Alyousef, Hisham Alabduljabbar and Abdeliazim Mustafa Mohamed: Department of Civil Engineering, College of Engineering, Prince Sattam bin Abdulaziz University, Al-kharj 11942, Saudi Arabia
Abdulaziz Alaskar and Fahed Alrshoudi: Department of Civil Engineering, College of Engineering, King Saud University, Riyadh 11362, Saudi Arabia




Abstract
During the last few decades, fluid viscous dampers have been significantly improved in terms of performance and reliability. Viscous dampers dissipate the input energy into heat and the increased temperature may damage internal seals of the damper. As a result, thermal compensation is crucial for almost all fluid viscous dampers. In this study, while referring to the main working principles of the recently developed bypass viscous damper in Iran, a comprehensive case study is conducted on a RC building having diagonal braces equipped with such viscous dampers. Experimental results of a small-scale bypass viscous damper is presented and it is shown that the currently available simplified Maxwell models can simulate behavior of the bypass viscous damper with good accuracy. Using a case study, contribution of bypass viscous dampers to seismic behavior of structural and non-structural elements are investigated. A designed procedure is adopted to increase damping ratio of the building from 3% to 15%. In this way, reductions of 25% and 13% in the required concrete and steel rebar materials have been achieved. From nonlinear time history analyses, it is observed that bypass viscous dampers can greatly improve seismic behavior of structural elements and non-structural elements.

Key Words
viscous damping; bypass viscous damper; energy dissipating device; numerical analysis; seismic behavior; non-structural Elements

Address
Reza Esfandiyari: Department of Civil Engineering, Islamic Azad University Central Tehran Branch,
Imam Hassan Blvd, Ashrafi Isfahani Highway, Tehran, Iran;
Behsazan Larzeh Davam Co., The Science and Technology Park of University of Tehran, North Kargar St., Tehran, Iran
Soheil Monajemi Nejad and Jafar Asgari Marnani: Department of Civil Engineering, Islamic Azad University Central Tehran Branch, Imam Hassan Blvd, Ashrafi Isfahani Highway, Tehran, Iran
Seyed Amin Mousavi: Behsazan Larzeh Davam Co., The Science and Technology Park of University of Tehran, North Kargar St., Tehran, Iran
Seyed Mehdi Zahrai: School of Civil Engineering, College of Engineering, University of Tehran, Enghelab Sq., 16th Azar St., Tehran, Iran,
also Adjunct Professor of Civil Engineering Department, the University of Ottawa, Canada




Abstract
The purpose of this paper is to investigate the degradation law of stiffness of steel-concrete composite beams after certain fatigue loads. First, six test beams with stud connectors were designed and fabricated for static and fatigue tests. The resultant failure modes under different fatigue loading cycles were compared. And an analysis was performed for the variations in the load-deflection curves, residual deflections and relative slips of the composite beams during fatigue loading. Then, the correlations among the stiffness degradation of each test beam, the residual deflection and relative slip growth during the fatigue test were investigated, in order to clarify the primary reasons for the stiffness degradation of the composite beams. Finally, based on the stiffness degradation function under fatigue loading, a calculation model for the residual stiffness of composite beams in response to fatigue loading cycles was established by parameter fitting. The results show that the stiffness of composite beams undergoes irreversible degradation under fatigue loading. And stiffness degradation is associated with the macrobehavior of material fatigue damage and shear connection degradation. In addition, the stiffness degradation of the composite beams exhibit S-shaped monotonic decreasing trends with fatigue cycles. The general agreement between the calculation model and experiment shows good applicability of the proposed model for specific beam size and fatigue load parameters. Moreover, the research results provide a method for establishing a stiffness degradation model for composite beams after fatigue loading.

Key Words
steel-concrete composite beam; fatigue; stiffness degradation; relative slip; bridge

Address
Bing Wang and Yong Ding: School of Civil and Environmental Engineering, Ningbo University, Ningbo 315211, China
Qiao Huang: School of Transportation, Southeast University, Nanjing 210096, China
Xiaoling Liu: Faculty of Maritime and Transportation, Ningbo University, Ningbo 315211, China

Abstract
In this research, a simple four-variable trigonometric integral shear deformation model is proposed for the static behavior of advanced functionally graded (AFG) ceramic-metal plates supported by a two-parameter elastic foundation and subjected to a nonlinear hygro-thermo-mechanical load. The elastic properties, including both the thermal expansion and moisture coefficients of the plate, are also supposed to be varied within thickness direction by following a power law distribution in terms of volume fractions of the components of the material. The interest of the current theory is seen in its kinematics that use only four independent unknowns, while first-order plate theory and other higher-order plate theories require at least five unknowns. The \"in-plane displacement field\" of the proposed theory utilizes cosine functions in terms of thickness coordinates to calculate out-of-plane shear deformations. The vertical displacement includes flexural and shear components. The elastic foundation is introduced in mathematical modeling as a two-parameter Winkler-Pasternak foundation. The virtual displacement principle is applied to obtain the basic equations and a Navier solution technique is used to determine an analytical solution. The numerical results predicted by the proposed formulation are compared with results already published in the literature to demonstrate the accuracy and efficiency of the proposed theory. The influences of \"moisture concentration\", temperature, stiffness of foundation, shear deformation, geometric ratios and volume fraction variation on the mechanical behavior of AFG plates are examined and discussed in detail.

Key Words
advanced functionally graded materials; four-variable integral plate theory; hygro-thermo-mechanical loading; elastic foundation

Address
Abdelouahed Tounsi: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran,Eastern Province, Saudi Arabia;
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
S.U. Al-Dulaijan, Mohammed A. Al-Osta, M.M. Al-Zahrani and Alfarabi Sharif: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran,Eastern Province, Saudi Arabia
Abdelbaki Chikh: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
Université Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algérie
Abdeldjebbar Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria



Abstract
This paper presents a new structural system to use as retaining walls. In civil works, there is a general trend to use traditional reinforced concrete (RC) retaining walls to resist soil pressure. Despite their good resistance, RC retaining walls have some disadvantages such as need for huge temporary formworks, high dense reinforcing, low construction speed, etc. In the present work, a composite wall with only one steel plate (steel–concrete) is proposed to address the disadvantages of the RC walls. In the proposed system, steel plate is utilized not only as tensile reinforcement but also as a permanent formwork for the concrete. In order to evaluate the efficiency of the proposed SC composite system, an experimental program that includes nine SC composite wall specimens is developed. In this experimental study, the effects of different parameters such as distance between shear connectors, length of shear connectors, concrete ultimate strength, use of compressive steel plate and compressive steel reinforcement are investigated. In addition, a 3D finite element (FE) model for SC composite walls is proposed using the finite element program ABAQUS and load-displacement curves from FE analyses were compared against results obtained from physical testing. In all cases, the proposed FE model is reasonably accurate to predict the behavior of SC composite walls under out-of-plane loads. Results from experimental work and numerical study show that the SC composite wall system has high strength and ductile behavior under flexural loads. Furthermore, the design equations based on ACI code for calculating out-of-plate flexural and shear strength of SC composite walls are presented and compared to experimental database.

Key Words
composite wall system; retaining wall; experimental work; FE model; flexural load

Address
Saeid Sabouri-Ghomi and Arman Nasri: Civil Engineering Department, K.N. Toosi University of Technology, Tehran, Iran
Younes Jahani : Analysis and Advanced Materials for Structural Design (AMADE), Polytechnic School, University of Girona, Girona, Spain
Anjan K. Bhowmick: 3Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, Canada


Abstract
Buckling restrained braces (BRBs) were developed as an enhanced alternative to conventional braces by restraining their global buckling, thus allowing development of a stable quasi-symmetric hysteretic response. A wider adoption of buckling restrained braced frames is precluded due to proprietary character of most BRBs and the code requirement for experimental qualification. To overcome these problems, BRBs with capacities corresponding to typical steel multi-storey buildings in Romania were developed and experimentally tested in view of prequalification. The first part of this paper presents the results of the experimental program which included sub-assemblage tests on ten full-scale BRBs and uniaxial tests on components materials (steel and concrete). Two different solutions of the core were investigated: milled from a plate and fabricated from a square steel profile. The strength of the buckling restraining mechanism was also investigated. The influence of gravity loading on the unsymmetrical deformations in the two plastic segments of the core was assessed, and the response of the bolted connections was evaluated. The cyclic response of BRBs was evaluated with respect to a set of performance parameters, and recommendations for design were given.

Key Words
buckling restrained brace; experimental testing; prequalification

Address
Aurel Stratan and Ciprian Ionut Zub: Department of Steel Structures and Structural Mechanics, Politehnica University of Timisoara, Ioan Curea, no. 1, 300224, Timisoara, Romania
Dan Dubina: Department of Steel Structures and Structural Mechanics, Politehnica University of Timisoara, Ioan Curea, no. 1, 300224, Timisoara, Romania;
Fundamental and Advanced Technical Research Centre, Romanian Academy, Timisoara Branch Bd. Mihai Viteazu, no. 24, 300223 Timisoara, Romania

Abstract
Buckling restrained braces (BRBs) were developed as an enhanced alternative to conventional braces by restraining their global buckling, thus allowing development of a stable quasi-symmetric hysteretic response. A wider adoption of buckling restrained braced frames is precluded due to proprietary character of most BRBs and the code requirement for experimental qualification. To overcome these problems, BRBs with capacities corresponding to typical steel multi-storey buildings in Romania were developed and experimentally tested in view of prequalification. In the second part of this paper, a complex nonlinear numerical model for the tested BRBs was developed in the finite element environment Abaqus. The calibration of the numerical model was performed at both component (material models: steel, concrete, unbonding material) and member levels (loading, geometrical imperfections). Geometrically and materially nonlinear analyses including imperfections were performed on buckling restrained braces models under cyclic loading. The calibrated models were further used to perform a parametric study aiming at assessing the influence of the strength of the buckling restraining mechanism, concrete class of the infill material, mechanical properties of steel used for the core, self-weight loading, and frame effect on the cyclic response of buckling restrained braces.

Key Words
buckling restrained brace; FEM model calibration; modelling of cyclic response; Abaqus

Address
Ciprian Ionut Zub and Aurel Stratan: Department of Steel Structures and Structural Mechanics, Politehnica University of Timisoara, Ioan Curea, no. 1, 300224, Timisoara, Romania
Dan Dubina: Department of Steel Structures and Structural Mechanics, Politehnica University of Timisoara, Ioan Curea, no. 1, 300224, Timisoara, Romania;
Fundamental and Advanced Technical Research Centre, Romanian Academy, Timisoara Branch
Bd. Mihai Viteazu, no. 24, 300223 Timisoara, Romania

Abstract
Light-Weight Concrete containing Expanded Poly-Styrene Beads (EPS-LWC) is an approved structural and non-structural material characterized by a considerably lower density and higher structural efficiency, compared to concrete containing ordinary aggregates. The experimental campaign carried out in this project provides new information on the mechanical properties of structural EPS-LWC, with reference to the strength and tension (by splitting and in bending), the modulus of elasticity, the stress-strain curve in unconfined compression, the absorbed energy under compression and reinforcement-concrete bond. The properties measured at seven ages since casting, from 3 days to 91 days, in order to investigate their in-time evolution. Mathematical relationships are formulated as well, between the previous properties and time, since casting. The dependence of the compressive strength on the other mechanical properties of EPS-LWC is also described through an empirical relationship, which is shown to fit satisfactorily the experimental results.

Key Words
expanded polystyrene; lightweight concrete; Splitting tensile strength; flexural strength; compressive stress-strain curve; energy absorption; bond-slip; age factor

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

Abstract
In this article, free vibration attributes of double-walled carbon nanotubes based on nonlocal elastic shell model have been investigated. For this purpose, a nonlocal Flügge shell model is established to observe the small scale effect. The wave propagation is employed to frame the governing equations as eigenvalue system. The influence of nonlocal parameter subjected to different end supports has been overtly examined. A suitable choice of material properties and nonlocal parameter been focused to analyze the vibration characteristics. The new set of inner and outer tubes radii investigated in detail against aspect ratio and length. The dominance of boundary conditions via nonlocal parameter is shown graphically. The results generated furnish the evidence regarding applicability of nonlocal shell model and also verified by earlier published literature.

Key Words
free vibration; nonlocal parameter; double-walled CNTs; Flügge shell model; wave propagation approach

Address
Sehar Asghar, Muhammad N. Naeem and Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38040, Faisalabad, Pakistan
Abdelouahed Tounsi: Faculty of Technology Civil Engineering Department, Materials 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
In this paper, free vibration analysis of a functionally graded cylindrical nanoshell resting on Pasternak foundation is presented based on the nonlocal elasticity theory. A two-dimensional formulation along the axial and radial directions is presented based on the first-order shear deformation shell theory. Hamilton\'s principle is employed for derivation of the governing equations of motion. The solution to formulated boundary value problem is obtained based on a harmonic solution and trigonometric functions for various boundary conditions. The numerical results show influence of significant parameters such as small scale parameter, stiffness of Pasternak foundation, mode number, various boundary conditions, and selected dimensionless geometric parameters on natural frequencies of nanoshell.

Key Words
size-dependent natural vibration; functionally graded materials; cylindrical nanoshell; nonlocal parameters; various boundary conditions

Address
Mohammad Arefi: Department of Solid Mechanics, University of Kashan, Kashan 87317-51167, Iran
Krzysztof Kamil Żur: Faculty of Mechanical Engineering, Bialystok University of Technology, Bialystok 15-351, Poland

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