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CONTENTS
Volume 47, Number 5, June 10 2023
 


Abstract
In this research, a new two-dimensional (2D) and quasi three-dimensional (quasi-3D) higher order shear deformation theory is devised to address the bending problem of functionally graded plates resting on an elastic foundation. The displacement field of the suggested theories takes into account a parabolic transverse shear deformation shape function and satisfies shear stress free boundary conditions on the plate surfaces. It is expressed as a combination of trigonometric and exponential shear shape functions. The Pasternak mathematical model is considered for the elastic foundation. The material properties vary constantly across the FG plate thickness using different distributions as power-law, exponential and Mori– Tanaka model. By using the virtual works principle and Navier's technique, the governing equations of FG plates exposed to sinusoidal and evenly distributed loads are developed. The effects of material composition, geometrical parameters, stretching effect and foundation parameters on deflection, axial displacements and stresses are discussed in detail in this work. The obtained results are compared with those reported in earlier works to show the precision and simplicity of the current formulations. A very good agreement is found between the predicted results and the available solutions of other higher order theories. Future mechanical analyses of three-dimensionally FG plate structures can use the study's findings as benchmarks.

Key Words
bending; functionally graded plate; shear deformation theory; stress; stretching effect; winkler-pasternak parameters

Address
Fatima Z. Zaoui and Djamel Ouinas:Laboratory of Science and Technology Environment and Valorization, Faculty of Sciences and Technology/Ibn Badis University,
27000 Mostaganem, Algeria

Abdelouahed Tounsi:1)Material and Hydrology Laboratory, Civil Engineering Department, Faculty of Technology / Djilali Liabes University,
22000 Sidi Bel Abbes, Algeria
2)Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia
3)YFL (Yonsei Frontier Lab), Yonsei University, Seoul 03722, Korea

Belkacem Achour and Tayyab A. Butt:Civil Engineering Department, University of Ha'il, KSA, Saudi Arabia

Jaime A. Vina Olay:Department of Materials Science and Metallurgical Engineering, University of Oviedo, Viesques Campus,33203 Gijon, Asturias, Spain

Abstract
This paper proposes an efficient approach for the structural topology optimization of bi-directional functionally graded structures by incorporating popular radial basis functions (RBFs) into an implicit level set (ILS) method. Compared to traditional element density-based methods, a level set (LS) description of material boundaries produces a smoother boundary description of the design. The paper develops RBF implicit modeling with multiquadric (MQ) splines, thin-plate spline (TPS), exponential spline (ES), and Gaussians (GS) to define the ILS function with high accuracy and smoothness. The optimization problem is formulated by considering RBF-based nodal densities as design variables and minimizing the compliance objective function. A LS-RBF optimization method is proposed to transform a Hamilton-Jacobi partial differential equation (PDE) into a system of coupled non-linear ordinary differential equations (ODEs) over the entire design domain using a collocation formulation of the method of lines design variables. The paper presents detailed mathematical expressions for BiDFG beams topology optimization with two different material models: continuum functionally graded (CFG) and mechanical functionally graded (MFG). Several numerical examples are presented to verify the method's efficiency, reliability, and success in accuracy, convergence speed, and insensitivity to initial designs in the topology optimization of two-dimensional (2D) structures. Overall, the paper presents a novel and efficient approach to topology optimization that can handle bi-directional functionally graded structures with complex geometries.

Key Words
continuum functionally graded steel; exponential spline; Gaussians; level set; micro-mechanical functionally graded; multiquadric; radial basis functions; thin plate spline; topology optimization

Address
Wonsik Jung, Thanh T. Banh, Nam G. Luuc and Dongkyu Lee:Department of Architectural Engineering, Sejong University, Seoul 05006, Republic of Korea

Abstract
The establishment of a hysteretic model which can accurately predict the hysteretic characteristics of the stud connection is of utmost importance for the seismic assessment of composite structures. In this paper, the Bouc-Wen-Baber-Noori (BWBN) model was adopted to describe the typical hysteretic characteristics of stud connections. Meanwhile, the NewtonRaphson iterative procedure and the Backward Euler method were used to determine the restoring force, and the Genetic Algorithm was employed to identify the parameters of the BWBN model based on the experimental data consisting of eight specimens. The accuracy of the identified parameters was demonstrated by comparison with the experimental data. Finally, prediction equations for the BWBN model parameters were developed in terms of the physical parameters of stud connections, which provides an approach to get the hysteretic response of stud connections conveniently.

Key Words
BWBN; combined load; cyclic loading; genetic algorithm; hysteretic model; stud connection

Address
Xi Qin:1)School of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China
2)Zhejiang Institute of Communications, Hangzhou 311100, China

Guotao Yang:School of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China

Abstract
Numerous methods have been proposed in predicting formability of sheet metals based on microstructural and macro-scale properties of sheets. However, there are limited number of papers on the optimization problem to increase formability of sheet metals. In the present study, we aim to use novel optimization algorithms in neural networks to maximize the formability of sheet metals based on tensile curve and texture of aluminum sheet metals. In this regard, experimental and numerical evaluations of effects of texture and tensile properties are conducted. The texture effects evaluation is performed using Taylor homogenization method. The data obtained from these evaluations are gathered and utilized to train and validate an artificial neural network (ANN) with different optimization methods. Several optimization method including grey wolf algorithm (GWA), chimp optimization algorithm (ChOA) and whale optimization algorithm (WOA) are engaged in the optimization problems. The results demonstrated that in aluminum alloys the most preferable texture is cube texture for the most formable sheets. On the other hand, slight differences in the tensile behavior of the aluminum sheets in other similar conditions impose no significant decreases in the forming limit diagram under stretch loading conditions.

Key Words
formability; crystalline texture; artificial intelligence (AI); Forming limits diagram (FLD); nonlocal effects; nano-scale size-dependency

Address
Fuyuan Dong and Junfeng Hou:1)School of Materials Science and Engineering, North Minzu University, Yinchuan 750021, Ningxia, China
2)Key Laboratory of Powders & Advanced Ceramics, North Minzu University, Yinchuan 750021, Ningxia, China

Wang Xu and Zhengnan Wu:School of Materials Science and Engineering, North Minzu University, Yinchuan 750021, Ningxia, China

Abstract
Steel corrosion induces structural deterioration of concrete-filled steel tubes (CFSTs), and any potential extreme action on a corroded CFST would pose a severe threat. This paper presents a comprehensive investigation on the lateral impact behaviour of CFSTs suffering from localised pitting corrosion damage. A refined finite element analysis model is developed for the simulation of locally corroded CFSTs subjected to lateral impact loads, which takes into account the strain rate effects on concrete and steel materials as well as the random nature of corrosion pits, i.e., the distribution patterns and the geometric characteristics. Full-range nonlinear analysis on the lateral impact behaviour in terms of loading and deforming time-history relations, nonlinear material stresses, composite actions, and energy dissipations are presented for CFSTs with no corrosion, uniform corrosion and pitting corrosion, respectively. Localised pitting corrosion is found to pose a more severe deterioration on the lateral impact behaviour of CFSTs due to the plastic deformation concentration, the weakened confinement and the reduction in energy absorption capacity of the steel tube. An extended parametric study is then carried out to identify the influence of the key parameters on the lateral impact behaviour of CFSTs with localised pitting corrosion. Finally, simplified design methods considering the features of pitting corrosion are proposed to predict the dynamic flexural capacity of locally pitted CFSTs subjected to lateral impact loads, and reasonable accuracy is obtained.

Key Words
composite action; concrete-filled steel tubes (CFSTs); dynamic flexural capacity; lateral impact; localised pitting corrosion

Address
Gen Li:1)Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, P. R. China
2)School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Chao Hou:Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, P. R. China

Luming Shen:School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia

Chuan-Chuan Hou:School of Transportation Science and Engineering, Beihang University, Beijing, 100191, P. R. China

Abstract
Taking a look at the previously published papers, it is revealed that there is a porosity index limitation (around 0.35) for the mechanical behavior analysis of the functionally graded porous (FGP) structures. Over mentioned magnitude of the porosity index, the elastic modulus falls below zero for some parts of the structure thickness. Therefore, the current paper is presented to analyze the vibrational behavior of the FGP Timoshenko beams (FGPTBs) using a novel refined formulation regardless of the porosity index magnitude. The silica aerogel foundation and various hydrothermal loadings are assumed as the source of external forces. To obtain the FGPTB's properties, the power law is hired, and employing Hamilton's principle in conjunction with Navier's solution method, the governing equations are extracted and solved. In the end, the impact of the various variables as different beam materials, elastic foundation parameters, and porosity index is captured and displayed. It is revealed that changing hygrothermal loading from non-linear toward uniform configuration results in non-dimensional frequency and stiffness pushing up. Also, Al – Al2O3 as the material composition of the beam and the porosity presence with the O pattern, provide more rigidity in comparison with using other materials and other types of porosity dispersion. The presented computational model in this paper hopes to help add more accuracy to the structures' analysis in high-tech industries.

Key Words
functionally graded porous structure; refined formulation; silica aerogel foundation; Timoshenko beam; various hygrothermal loading; vibration

Address
Mohammad Khorasani:1)Department of Mechanical & Industrial Engineering, Louisiana State University, 3304 S Quad Dr, LA 70803, Baton Rouge, U.S.A.
2)Department of Basic and Applied Sciences for Engineering, Sapienza University, Via Scarpa 16, 00161, Rome, Italy

Luca Lampani:Department of Mechanical and Aerospace Engineering, Sapienza University, Via Eudossiana 18, 00184, Rome, Italy

Abdelouahed Tounsi:1)Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia
2)Yonsei Frontier Laboratory, Yonsei University, Seoul, Korea

Abstract
Concrete-filled steel tubular columns with double inner steel tubes (CFST-DIST) are a novel type of composite members developed from conventional concrete-filled steel tubular (CFST) columns. This paper investigates the structural performance of circular CFST-DIST stub columns using nonlinear finite element (FE) analysis. A numerical model was developed and verified against existing experimental test results. The validated model was then used to compare circular CFSTDIST stub columns' behavior with their concrete-filled double skin steel tubular (CFDST) and CFST counterparts. A parametric study was performed to ascertain the effects of geometric and material properties on the axial performance of CFST-DISTs. The FE results and the available test data were used to assess the accuracy of the European and American design regulations in predicting the axial compressive capacity of circular CFST-DIST stub columns. Finally, a new design model was recommended for estimating the compressive capacity of CFST-DISTs. Results clarified that circular CFST-DIST columns had the advantages of their CFST counterparts but with better ductility and strength-to-weight ratio. Besides, the investigated design codes led to conservative predictions of the compressive capacity of circular CFST-DIST columns.

Key Words
composite structure; concrete-filled; finite element; nonlinear analysis; steel tubular column

Address
Pouria Ayough and Yu-Hang Wang: School of Civil Engineering, Chongqing University, Chongqing 400045, China

Zainah Ibrahim: Department of Civil Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

Abstract
The self-centering energy-dissipating coupled wall panels (SECWs) possess a dual capacity of resiliency and energy dissipation. Used in steel frames, the SECWs can localize the damage of structures and reduce residual drifts. Based on OpenSEES, the nonlinear models were established and validated by experimental results. The seismic design procedure of steel frame with SECW structures (SF-SECW) was proposed in accordance with four-level seismic fortification objectives. Nonlinear time-history response analyses were carried out to validate the reasonability of seismic design procedure for 6-story and 12-story structures. Results show that the inter-story drifts of designed structures are less than drift limits. According to incremental dynamic analyses (IDA), the fragility curves of mentioned-above structure models under different limit states were obtained. The results indicate that designed structures have good seismic performance and meet the seismic fortification objectives.

Key Words
seismic collapse; seismic performance; self-centering; steel moment frames; wall panels

Address
Lu Sui, Hanheng Wu, Menglong Tao, Zhichao Jia and Tianhua Zhou:School of Civil Engineering, Chang'an University, Xi'an 710061, China


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