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CONTENTS
Volume 43, Number 6, June25 2022
 

Abstract
Thin-walled square concrete-filled double steel tubular (CFDST) columns composed of the inner circular tube filled with concrete can be used to carry the large axial loads or strengthen existing CFST columns in composite constructions. This paper reports an experimental program carried out on short square CFDST columns loaded concentrically. The influences of important column parameters on the post-buckling performance of such columns are investigated. Test results exhibit that the inner circular tube significantly improves the ultimate loads and the ductility of such columns compared to conventional concrete-filled steel tubular (CFST) and double-skin CFST (DCFST) columns with an inner void. A mathematical model developed is used to simulate the ultimate strengths and load-strain curves of such columns loaded axially. Furthermore, the ultimate strengths of such columns are predicted using existing codified design models for conventional CFST columns as well as the formulas proposed by previous researchers and compared against a large database comprising 500 CFDST columns. Lastly, an accurate artificial neural network model is developed for the practical applications of such columns under axial loading.

Key Words
artificial neural network; axial loading; CFDST columns; post-buckling; short columns

Address
Junchang Ci:College of Architecture and Civil Engineering, Beijing University of Technology, Beijing, P.R. China

Mizan Ahmed Viet-Linh Tran:1)College of Architecture and Civil Engineering, Beijing University of Technology, Beijing, P.R. China 2)School of Civil and Mechanical Engineering, Curtin University, Kent St, Bentley, WA 6102, Australia

Hong Jia:CRCC Development Group Co. Ltd., Beijing, P.R. China

Shicai Chen:College of Architecture and Civil Engineering, Beijing University of Technology, Beijing, P.R. China

Tan N. Nguye:Department of Architectural Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul, 05006, Republic of Korea

Abstract
This article aims to investigate the size dependent bending behavior of perforated nanobeams incorporating the nonlocal and the microstructure effects based on the nonlocal strain gradient elasticity theory (NSGET). Shear deformation effect due to cutout process is studied by using Timoshenko beams theory. Closed formulas for the equivalent geometrical characteristics of regularly squared cutout shape are derived. The governing equations of motion considering the nonlocal and microstructure effects are derived in comprehensive procedure and nonclassical boundary conditions are presented. Analytical solution for the governing equations of motion is derived. The derived non-classical analytical solutions are verified by comparing the obtained results with the available results in the literature and good agreement is observed. Numerical results are obtained and discussed. Parametric studies are conducted to explore effects of perforation characteristics, the nonclassical material parameters, beam slenderness ratio as well as the boundary and loading conditions on the non-classical transverse bending behavior of cutout nanobeams. Results obtained are supportive for the design, analysis and manufacturing of such nanosized structural system.

Key Words
analytical solution; filling ratio; nanobeams, nonclassical effects; nonlocal strain gradient theory; shear deformation; squared cutout; static bending

Address
Mashhour A. Alazwari:Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia

Mohamed A. Eltaher:1)Mechanical Engineering Department, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah, Saudi Arabia
2)Mechanical Design & Production Department, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt

Alaa A. Abdelrahman:Mechanical Design & Production Department, Faculty of Engineering, Zagazig University,P.O. Box 44519, Zagazig, Egypt

Abstract
In this paper, buckling analyses of nanocomposite plate reinforced by Graphen platelet (GPL) is studied. The Halphin-Tsai model is used for obtaining the effective material properties of nanocomposite plate. The nanocomposite plate is modeled by Third order shear deformation theory (TSDT). The elastic medium is simulated by Winkler model. Employing relations of strains-displacements and stress-strain, the energy equations of the plate are obtained and using Hamilton's principle, the governing equations are derived. The governing equations are solved based on analytical solution. The effect of GPL volume percent, geometrical parameters of plate and elastic foundation on the buckling load are investigated. Results show that with increasing GPLs volume percent, the buckling load increases. In addition, elastic medium can enhance the values of buckling load significantly.

Key Words
analytical solution; buckling; GPL; nanocomposite plate; TSDT

Address
Linyun Zhou:School of Transportation, Southeast University, Nanjing 210096, Jiangsu, China

Yasaman Najjari:Department of Civil Engineering, Faculty of Engineering and Technology, University of Mazandaran, Babolsar, Iran

Abstract
The behavior of shear deficient under-balanced reinforced concrete beams with rectangular cross-sections, which were externally strengthened with CFRP composite along shear spans, was experimentally investigated under vertical load. One of the specimens represents a reference beam without CFRP strengthening and the other specimens have different width/strip spacing ratios (wf/sf). The optimum strip in terms of wf/sf, which will bring the beam behavior to the ideal level in terms of strength and ductility, was determined according to the regulations. When the wf/sf ratio exceeds 0.55, the behavior of the beam shifted from shear failure to bending failure. However, it has been observed that the wf/sf ratio should be increased up to 0.82 in order for the beam to reach sufficient shear reserve value according to the codes. It is also observed that the direction and weight of the CFRP composite are one of the most critical factors and 240 gr/m2 CFRP strips experienced sudden ruptures in the shear span after the cracking of the concrete. It is considered as a deficiency that the empirical shear capacity formulas given for the beams reinforced with CFRP in the regulations do not take into account both direction and weight of CFRP composites.

Key Words
CFRP composite; damage history analysis; Optimum FRP; reinforced concrete beam; shear deficient; strengthening

Address
Lokman Gemi:Meram Vocational School, Necmettin Erbakan University, 42100, Konya, Turkey

Mohammed Alsdudi:Department of Civil Engineering, Konya Technical University, 42130, Konya, Turkey

Ceyhun Aksoylu:Department of Civil Engineering, Konya Technical University, 42130, Konya, Turkey

Sakir Yazman:Ilgin Vocational School, Selcuk University, 42615, Konya, Turkey

Yasin Onuralp Ozkili:Department of Civil Engineering, Necmettin Erbakan University, 42100, Konya, Turkey

Musa Hakan Arslan:Department of Civil Engineering, Konya Technical University, 42130, Konya, Turkey

Abstract
Concrete-filled double skinned steel tubular (CFDST) columns have been used to construct modern structures such as tall buildings and bridges as well as infrastructures as they provide better, lesser weight, and greater stiffness in structural performance than conventional reinforced concrete or steel members. Different shapes of CFDST columns may be needed to satisfy the architectural and aesthetic criteria. In the study, three-dimensional FE simulations of circular and elliptical CFDST columns under axial compression were developed and verified through the experimental test data from the perspectives of full load-displacement histories, ultimate axial strengths, and failure modes. The verified FE models were used to investigate and compare the structural performance of CFDST columns with circular and elliptical cross-section shapes by evaluating the overall load-deformation curves, interaction stress-deformation responses, and composite actions of the column. At last, the accuracy of available design models in predicting the ultimate axial strengths of CFST columns were investigated. Research results showed that circular and elliptical CFDST column behaviors were generally similar. The overall structural performance of circular CFDST columns was relatively improved compared to the elliptical CFDST column.

Key Words
axial compression; composite actions; Concrete-filled double skinned steel tubes (CFDST); finite element non-linear analysis

Address
Manigandan R and Manoj Kumar:Department of Civil Engineering, Birla Institute of Technology and Science, Pilani (BITS Pilani), Vidya Vihar, Rajasthan 333 301, India

Abstract
This paper aims to investigate the axial compressive behavior of reinforced concrete (RC) columns strengthened with self-compacting and micro-expanding (SM) concrete-filled steel tubes (SM-CFSTs). Nine specimens were tested in total under the local axial compression. The test parameters included steel tube thickness, filling concrete strength, filling concrete type and initial axial preloading. The test results demonstrated that the initial stiffness, ultimate bearing capacity and ductility of original RC columns were improved after being strengthened by SM-CFSTs. The ultimate bearing capacity of the SM-CFST strengthened RC columns was significantly enhanced with the increase of steel tube thickness. The initial stiffness and ultimate bearing capacity of the SM-CFST strengthened RC columns were slightly enhanced with the increase of filling concrete strength. However, the effect of filling concrete type and initial axial preloading of the SM-CFST strengthened RC columns were negligible. Three equations for predicting the ultimate bearing capacity of the SM-CFST strengthened RC columns were compared, and the modified equation based on Chinese code (GB 50936-2014) was more precise.

Key Words
axial behavior; concrete-filled steel tube; initial axial preloading; local compression; self-compacting and micro-expanding concrete; strengthening

Address
Haibo Jiang, Jiahang Li, Quan Cheng and Jie Xiao:School of Civil and Transportation Engineering, Guangdong Univ. of Technology, Guangzhou Higher Education Mega Center, Guangzhou,
510006, China

Zhenkan Chen:The Maintaining Branch, Guangzhou Communication Investment Group Co. Ltd., Guangzhou, 511430, China

Abstract
Concrete-encased steel (CES) beam, in which structural steel is encased in a reinforced concrete (RC) section, is widely applied in high-rise buildings as transfer beams due to its high load-carrying capacity, great stiffness, and good durability. However, these CES beams are prone to shear failure because of the low shear span-to-depth ratio and the heavy load. Due to the high load-carrying capacity and the brittle failure process of the shear failure, the accurate strength prediction of CES beams significantly influences the assessment of structural safety. In current design codes, design formulas for predicting the shear strength of CES beams are based on the so-called "superposition method". This method indicates that the shear strength of CES beams can be obtained by superposing the shear strengths of the RC part and the steel shape. Nevertheless, in some cases, this method yields errors on the unsafe side because the shear strengths of these two parts cannot be achieved simultaneously. This paper clarifies the conditions at which the superposition method does not hold true, and the shear strength of CES beams is investigated using a compatible truss-arch model. Considering the deformation compatibility between the steel shape and the RC part, the method to obtain the shear strength of CES beams is proposed. Finally, the proposed model is compared with other calculation methods from codes AISC 360 (USA, North America), Eurocode 4 (Europe), YB 9082 (China, Asia), JGJ 138 (China, Asia), and AS/NZS 2327 (Australia/New Zealand, Oceania) using the available test data consisting of 45 CES beams. The results indicate that the proposed model can predict the shear strength of CES beams with sufficient accuracy and safety. Without considering the deformation compatibility, the calculation methods from the codes AISC 360, Eurocode 4, YB 9082, JGJ 138, and AS/NZS 2327 lead to excessively conservative or unsafe predictions.

Key Words
concrete-encased steel; deformation compatibility; design codes; shear strength; truss-arch model

Address
Yicong Xue:School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an, Shaanxi 710055, China

Chongxin Shang:School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an, Shaanxi 710055, China

Yong Yang:1)School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an, Shaanxi 710055, China
2)Key Lab of Structural Engineering and Earthquake Resistance of the Ministry of Education, Xi'an University of Architecture & Technology,
Xi'an, Shaanxi 710055, China

Yunlong Yu:1)School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an, Shaanxi 710055, China
2)Key Lab of Structural Engineering and Earthquake Resistance of the Ministry of Education, Xi'an University of Architecture & Technology,
Xi'an, Shaanxi 710055, China

Zhanjie Wang:New Era (Xi'an) Design Engineering Co., Ltd, Xi'an, Shaanxi 710018, China

Abstract
This paper presents an investigation on the free vibration characteristics of functionally graded nanocomposite double-beams reinforced by single-walled carbon nanotubes (SWCNTs). The double-beams coupled by an interlayer spring, resting on the elastic foundation with a linear layer and shear layer, and is simply supported in thermal environments. The SWCNTs gradient distributed in the thickness direction of the beam forms different reinforcement patterns. The materials properties of the functionally graded carbon nanotube-reinforced composites (FG-CNTRC) are estimated by rule of mixture. The first order shear deformation theory and Euler-Lagrange variational principle are employed to derive the motion equations incorporating the thermal effects. The vibration characteristics under several patterns of reinforcement are presented and discussed. We conducted a series of studies aimed at revealing the effects of the spring stiffness, environment temperature, thickness ratios and carbon nanotube volume fraction on the nature frequency.

Key Words
double beam; first order shear deformation theory; functionally graded carbon nanotube-reinforced composite; thermal environment; vibration characteristics

Address
Jing-Lei Zhao, Xu Chen, Gui-Lin She, Yan Jing, Ru-Qing Bai, Jin Yi, Hua-Yan Pu and Jun Lu:College of Mechanical and vehicle Engineering, Chongqing University, Chongqing,400044, China

Abstract
This paper proposes a method to predict the deflection of prestressed concrete (PC) beams with corrugated steel web (CSW) under constant load concerning time-dependent variation in concrete material. Over time, the top and bottom concrete slabs subjected to asymmetric compression experience shrinkage and creep deformations. Here, the classical EulerBernoulli beam theory assumption that the plane sections remain plane is not valid due to shear deformation of CSW. Therefore, this study presents a method based on the first-order shear deformation to find the long-term deflection of the composite beams under bending by considering time effects. Two experimental prestressed beams of this type were monitored under their selfweight over time, and the theoretical results were compared with those data. Additionally, 3D analytical models of the experimental beams were used according to material properties, and the results were compared with two previous cases. There was good consistency between the analytical and numerical results with low error, which increased by wave radius. It is concluded that the proposed method could reliably be used for design purposes.

Key Words
Corrugated Steel Web (CSW); creep; long-term deflection; Prestressed Concrete (PC); relaxation; shrinkage

Address
Hamid Reza Ebrahimi Motlagh and Alireza Rahai:Department of Civil and Environmental Engineering, Amirkabir University of Technology (Tehran Polytechnic), No. 350, Hafez Ave.,
1591634311 Tehran, Iran

Abstract
This research is devoted to study the effects of humidity and temperature on the bending behavior of functionally graded (FG) ceramic-metal porous plates resting on Pasternak elastic foundation using a quasi-3D hyperbolic shear deformation theory developed recently. The present plate theory with only four unknowns, takes into account both transverse shear and normal deformations and satisfies the zero traction boundary conditions on the surfaces of the functionally graded plate without using shear correction factors. Material properties of porous FG plate are defined by rule of the mixture with an additional term of porosity in the through-thickness direction. The governing differential equations are obtained using the "principle of virtual work". Analytically, the Navier method is used to solve the equations that govern a simply supported FG porous plate. The obtained results are checked by comparing the results determined for the perfect and imperfect FG plates with those available in the scientific literature. Effects due to material index, porosity factors, moisture and thermal loads, foundation rigidities, geometric ratios on the FG porous plate are all examined. Finally, this research will help us to design advanced functionally graded materials to ensure better durability and efficiency for hygro-thermal environments.

Key Words
functionally graded materials; porosity; hygrothermal; thickness stretching; elastic foundation

Address
Ikram Kheira Bot:Industrial Engineering and Sustainable Development Laboratory, University of Relizane, Faculty of Science & Technology, Mechanical
Engineering Department, Algeria

Abdelmoumen Anis Bousahla:Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria

Amine Zemri:University of Relizane, Faculty of Science & Technology, Civil Engineering Department, Algeria

Mohamed Sekkal:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
2)Universite des sciences et de la technologie Houari-Boumediene, Faculte de Genie Civil, Departement structures et materiaux, Alger, Algerie

Abdelhakim Kaci:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria 2)Universite Dr Tahar Moulay, Faculte de Technologie, Departement de Genie Civil et Hydraulique, BP 138 Cite En-Nasr 20000 Saida, Algerie

Fouad Bourada:1)Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria 2)Departement des Sciences et de la Technologie, Universite de Tissemsilt, BP 38004 Ben Hamouda, Algerie

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

M.H. Ghazwani:Department of Mechanical Engineering, Faculty of Engineering, Jazan University, P.O box 45124, Jazan, Kingdom of Saudia Arabia

S.R. Mahmoud:GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia

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