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Volume 35, Number 5, June10 2020

Experimental investigation and finite element analysis of corroded cold-formed steel (CFS) columns are presented. 11 tensile coupon specimens and 6 stub columns of corroded CFS that had a channel section of C160x60x20 were subjected to monotonic tensile tests and axial compression tests, respectively. The degradation laws of the mechanical properties of the tensile coupon specimens and stub columns were analysed. An appropriate finite element model for the corroded CFS columns was proposed and the influence of local corrosion on the stability performance of the columns was studied by finite element analysis. Finally, the axial capacity of the experimental results was compared with the predictions obtained from the existing design specifications. The results indicated that with an increasing average thickness loss ratio, the ultimate strength, elastic modulus and yield strength decreased for the tensile coupon specimens. Local buckling deformation was not noticeable until the load reached about 90% of the ultimate load for the non-corroded columns, while local buckling deformation was observed when the load was only 40% of the ultimate load for the corroded columns. The maximum reduction of the ultimate load and critical buckling load was 57% and 81.7%, respectively, compared to those values for the non-corroded columns. The ultimate load of the columns with web thickness reduced by 2 mm was 53% lower than that of the non-corroded columns, which indicates that web corrosion most significantly affects the bearing capacity of the columns with localized corrosion. The results predicted using the design specifications of MOHURD were more accurate than those predicted using the design specifications of AISI.

Key Words
cold-formed steel; mechanical properties; corrosion; finite element analysis; columns

Nie Biao, Xu Shanhua, Zhang Haijiang and Zhang Zongxing: School of Civil Engineering, Xi\'an University of Architecture & Technology, No.13, middle section of Yanta Road, Beilin District, China

The past years were marked by an increase in the use of wood waste in civil and mechanical constructions. Date palm waste remains also one of the most solicited renewable and recyclable natural resources in the composition of composite materials. In Algeria, a great amount of this type of plant wastes accumulates every year. In order to make use of this waste, a new wood-epoxy composite material based on date palm petiole particleboard is developed. It makes use of date palm petiole particleboard as reinforcement and epoxy resin as matrix. The size of the particles reinforcement are between 1~3 mm and proportion of reinforcement used is 37%. In this work, experimental and numerical studies are conducted in order to characterize the wood fibre-epoxy plates. Firstly, experimental modal analysis test was carried out to determine Young\'s modulus of the elaborated material. Then, in order to validate the results, compression test was conducted. Furthermore, additional information about the shear modulus of this material is obtained by performing an experimental modal analysis to extract the first torsional mode. Moreover, a finite element model is developed using ANSYS software to simulate the vibration behaviour of the plates. The results show a good agreement with the experimental modal analysis, which confirms the values of Young

Key Words
palm; wood-epoxy composite; experimental analysis; finite element analysis

A. Bendada and D. Boutchicha: Laboratoire de Mécanique Appliquée, Université des Sciences et de la Technologie d\'Oran - Mohamed Boudiaf. Algeria
S. Khatir: Soete Laboratory, Faculty of Engineering and Architecture, Ghent University,
Technologiepark Zwijnaarde 46, B-9052 Zwijnaarde, Belgium
E. Magagnini and R. Capozucca: DICEA, Università Politecnica delle Marche, Ancona, Italy
M. Abdel Wahab: Division of Computational Mechanics, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam

The buckling analysis of the embedded sinusoidal piezoelectric beam is evaluated using numerical method. The smart beam is subjected to external voltage in the thickness direction. Elastic medium is simulated with two parameters of spring and shear. The structure is modelled by sinusoidal shear deformation theory (SSDT) and utilizing energy method, the final governing equations are derived on the basis of piezo-elasticity theory. In order to obtaining the buckling load, the differential quadrature method (DQM) is used. The obtained results are validated with other published works. The effects of beam length and thickness, elastic medium, boundary condition and external voltage are shown on the buckling load of the structure. Numerical results show that with enhancing the beam length, the buckling load is decreased. In addition, applying negative voltage, improves the buckling load of the smart beam.

Key Words
smart beam; buckling; SSDT; numerical method; elastic medium

Pouyan Talebizadehsardari: Metamaterials for Mechanical, Biomechanical and Multiphysical Applications Research Group, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, Vietnam
Arameh Eyvazian: Mechanical and Industrial Engineering Department, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar
Mojtaba Gorji Azandariani: Structural Engineering Division, Faculty of Civil Engineering, Semnan University, Semnan, Iran
Trong Nhan Tran: Faculty of Automobile Technology, Van Lang University, Ho Chi Minh City, Vietnam
Dipen Kumar Rajak: Department of Mechanical Engineering, Sandip Institute of Technology and Research Centre, Nashik 422213, MH-India
Roohollah Babaei Mahani: Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam;
Faculty of Civil Engineering, Duy Tan University, Da Nang 550000, Vietnam

A unique lightweight string truss deployable bridge assembled by thin-walled fiber reinforced polymer (FRP) and metal profiles was designed for emergency applications. As a new structure, investigations into the static structural performance under the serviceability limit state are desired for examining the structural integrity of the developed bridge when subjected to unsymmetrical loadings characterized by combined torsion and bending. In this study, a full-scale experimental inspection was conducted on a fabricated bridge, and the combined flexural–torsional behavior was examined in terms of displacement and strains. The experimental structure showed favorable strength and rigidity performances to function as deployable bridge under unsymmetrical loading conditions and should be designed in accordance with the stiffness criterion, the same as that under symmetrical loads. In addition, a finite element model (FEM) with a simple modeling process, which considered the multi segments of the FRP members and realistic nodal stiffness of the complex unique hybrid nodal joints, was constructed and compared against experiments, demonstrating good agreement. A FEM-based numerical analysis was thereafter performed to explore the effect of the change in elastic modulus of different FRP elements on the static deformation of the bridge. The results confirmed that the change in elastic modulus of different types of FRP element members caused remarkable differences on the bending and torsional stiffness of the hybrid bridge. The global stiffness of such a unique bridge can be significantly enhanced by redesigning the critical lower string pull bars using designable FRP profiles with high elastic modulus.

Key Words
composite structure; string structure; deployable bridge; spatial truss; extrusion-type fiber reinforced polymer (FRP); static loading test; finite element analysis (FEA)

Dongdong Zhang, Jiaxin Yuan, Feng Li,
Yifeng Gao, Ruijie Zhu and Zhiqin Zhao: College of Field Engineering, Army Engineering University of PLA,
No.1 Haifuxiang, Qinhuai District, Nanjing, 210007, P. R. China
Qilin Zhao: College of Mechanical and Power Engineering, Nanjing Tech University,
No.1 Puzhu south road, Pukou District, Nanjing, 211800, P. R. China

This paper proposes the use of a porous core between layers of laminated composite plates to examine its effect on the natural frequencies of the resulted porous laminated composite sandwich plate (PLCSP) resting on a two-parameter elastic foundation. Moreover, it has been suggested that the dispersion of porosity has two different functionally graded (FG) patterns which are compared with a uniformly dispersed (UD) profile to find their best vibrational efficiency in the proposed PLCSPs. In FG patterns, two types of dispersions, including symmetric (FG-S) and asymmetric (FG-A) patterns have been considered. To derive the governing Eigen value equation of such structures, the first order shear deformation theory (FSDT) of plates has been employed. Accordingly, a finite element method (FEM) is developed to solve the derived Eigen value equation. Using the mentioned theory and method, the effects of porosity parameters, fiber orientation of laminated composite, geometrical dimensions, boundary conditions and elastic foundation on the natural frequencies of the proposed PLCSPs have been studied. It is observed that embedding porosity in core layer leads to a significant improvement in the natural frequencies of PLCSPs. Moreover, the natural frequencies of PLCSPs with FG porous core are higher than those with UD porous core.

Key Words
porous core; laminated composite; functionally graded; sandwich plate; free vibrations

Babak Safaei: Department of Mechanical Engineering, Eastern Mediterranean University, G. Magosa, TRNC Mersin 10, Turkey

This manuscript presents impacts of gradation of material functions and axial load functions on critical buckling loads and mode shapes of functionally graded (FG) thin and thick beams by using higher order shear deformation theory, for the first time. Volume fractions of metal and ceramic materials are assumed to be distributed through a beam thickness by both sigmoid law and symmetric power functions. Ceramic–metal–ceramic (CMC) and metal–ceramic–metal (MCM) symmetric distributions are proposed relative to mid-plane of the beam structure. The axial compressive load is depicted by constant, linear, and parabolic continuous functions through the axial direction. The equilibrium governing equations are derived by using Hamilton\'s principles. Numerical differential quadrature method (DQM) is developed to discretize the spatial domain and covert the governing variable coefficients differential equations and boundary conditions to system of algebraic equations. Algebraic equations are formed as a generalized matrix eigenvalue problem, that will be solved to get eigenvalues (buckling loads) and eigenvectors (mode shapes). The proposed model is verified with respectable published work. Numerical results depict influences of gradation function, gradation parameter, axial load function, slenderness ratio and boundary conditions on critical buckling loads and mode-shapes of FG beam structure. It is found that gradation types have different effects on the critical buckling. The proposed model can be effective in analysis and design of structure beam element subject to distributed axial compressive load, such as, spacecraft, nuclear structure, and naval structure.

Key Words
buckling stability; variable axial load; FG sigmoid distribution; higher beam theory; variable-coefficients differential equations; Differential Quadrature Method (DQM)

Ammar Melaibari: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia;
Centre of Nanotechnology, King Abdulaziz University, Jeddah, Saudi Arabia
Ahmed B. Khoshaim: Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia
Salwa A. Mohamed: Department of Engineering Mathematics, 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 Department, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt

This paper focus on the buckling restrained braces (BRBs) with new casing members (CMs). Seven BRBs with CMs consisting of precast concrete modules (PCMs) were tested to investigate the effects of CMs on the cyclic performance of BRBs. The PCMs consisted of plain and reinforced concrete casted into wooden or steel molds than they were located on the core plate (CP) via bolts. There were 14 or 18 PCMs on the CP for each BRBs. The technique of the PCMs for the CM provides that the BRBs can be constructed inside the steel or reinforced concrete (RC) structures. In this way, their applications may be rapid and practical during the application of the retrofitting. The test results indicated that the cyclic performance of the BRBs was dominated by the connection strength and confinement of the PCMs. The BRBs with PCMs wrapped with fiber reinforced polymers (FRPs) sustained stable hysteretic performance up to a CP strain of 2.0 %. This indicates that the new designed BRBs with PCMs were found to be acceptable in terms of cyclic performance. Furthermore, the connection details, isolation materials and their application techniques have been also investigated for the improved BRB design in this study.

Key Words
buckling restrained braces; composite member; cyclic test; out-of-plane buckling

Ramazan Ozcelik, Kazim B. Civelek, Elif F. Erdil and Ferhat Erdal: Department of Civil Engineering, Akdeniz University, 07058, Antalya, Turkey
Yagmur Dikiciasik: Department of Civil Engineering, Karamanoglu Mehmetbey University,70100, Karaman, Turkey

Steel storage racks are lightweight structures, made of thin-walled cold-formed members, whose behaviour is remarkably influenced by local, distortional and overall buckling phenomena, frequently mutually combined. In addition, the need of an easy and rapid erection and reconfiguration of the skeleton frame usually entails the presence of regular perforations along the length of the vertical elements (uprights). Holes and slots strongly influence their behaviour, whose prediction is however of paramount importance to guarantee an efficient design and a safe use of racks. This paper focuses on the behaviour of isolated uprights subjected to both axial load and bending moments, differing for the cross-section geometry and for the regular perforation systems. According to the European standards for routine design, four alternatives to evaluate the bending moment–axial load resisting domains are shortly discussed and critically compared in terms of member load carrying capacity.

Key Words
thin-walled members; storage racks; uprights; perforated beam-columns; design methods; M-N domains

Nadia Baldassino and Martina Bernardi: Department of Civil, Environmental and Mechanical Engineering, Università di Trento, via Mesiano, 77, 38123, Trento, Italy
Claudio Bernuzzi and Marco Simoncelli: Department of Architecture, Built Environment and Construction Engineering, Politecnico di Milano,
piazza Leonardo da Vinci 32, 20133, Milano, Italy

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