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CONTENTS
Volume 41, Number 2, October25 2021
 

Abstract
This paper proposes an improved triangular element based on the strain approach and the Reissner-Mindlin theory to investigate the static, free vibration, and buckling response of functionally graded porous (FGP) nano-plates resting on the Parternak's two-parameter elastic medium foundation. The internal pores of nano-plates are described by two distribution laws, including uneven porosity distribution and logarithmic-uneven porosity distribution. Using Hamilton's principle, equilibrium equations of FGP nano-plates lying on a two-parameter foundation are obtained. The most remarkable feature of the improved triangular element is the degrees of freedom of elements approximated by Lagrange functions for the membrane strain and by the high-degree polynomial functions for the bending strain. The numerical results of the present work are compared with the available results in the literature to evaluate the performance of the proposed approach. Effects of geometrical and material properties such as the power-law index n, the porosity coefficient S, the nonlocal coefficient u, and the parameters of the elastic foundation on the static, free vibration, and buckling behavior of the FGP nano-plates are examined in detail.

Key Words
elastic foundation; FEM; FGP plates; nano-plates; nonlocal elasticity theory; Reissner-Mindlin theory; triangular element

Address
Quoc-Hoa Pham: Faculty of Mechanical Engineering, Industrial University of Ho Chi Minh City, Ho Chi Minh City, Vietnam
Phu-Cuong Nguyen: Advanced Structural Engineering Laboratory, Faculty of Civil Engineering,
Ho Chi Minh City Open University, Ho Chi Minh City, Vietnam
Van-Ke Tran: Department of Mechanics, Le Quy Don Technical University, Hanoi, Vietnam
Trung Nguyen-Thoi: Division of Computational Mathematics and Engineering, 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

Abstract
This paper presents an original high-order shear and normal deformation theory for the static and free vibration of sandwich plates. The number of unknowns and governing equations of the present theory is reduced, and hence makes it simple to use. Unlike any other theory, the number of unknown functions involved in displacement field is only four, as against five or more in the case of other shear and normal deformation theories. New types of functionally graded materials (FGMs) sandwich plates are considered, namely, both FG face sheets which the properties vary according to power-law function and exponentially graded hard core. The equations of motion for the present problem are derived from Hamilton' principle. For simply-supported boundary conditions, Navier's approach is utilized to solve the motion equations. The accuracy of the present theory is verified by comparing the obtained results with three-dimensional elasticity solutions and other quasi-3D higher-order theories reported in the literature. Other numerical examples are also presented to show the influences of the volume fraction distribution, geometrical parameters and power law index on the bending and free vibration responses of the FGM sandwich plates are studied. It can be concluded that present formulation which takes into account both the transverse shear and normal deformation, predicts the natural frequencies with the same degree of accuracy as that of 3D elasticity solutions and gives a good results of displacements and stress compared with others Quasi-3D theories. It can be also deduced that the central deflection is in direct correlation relation with inhomogeneity parameter and the natural frequency is in inverse relation with this parameter.

Key Words
bending and free vibration analysis; functionally graded plate; new quasi-3D theory; new type of sandwich plate; refined plate theory

Address
Djilali Kouider and Abdeldjebbar Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology,
Department of Civil Engineering, Algeria
Abdelhakim Kaci: Université Dr Tahar Moulay, Faculté de Technologie, Département de Génie Civil et Hydraulique,
BP 138Cité En-Nasr 20000 Saida, Algérie
Mahmoud M. Selim: Department of Mathematics, Al-Aflaj College of Science and Humanities, Prince Sattam bin Abdulaziz University, Al-Aflaj 710-11912 Saudi Arabia
Abdelmoumen Anis Bousahla: Laboratoire de Modélisation et Simulation Multi-échelle, Université de Sidi Bel Abbés, Algeria
Fouad Bourada: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology,
Department of Civil Engineering, Algeria;
Département des Sciences et de la Technologie, université de Tissemsilt, BP 38004 Ben Hamouda, Algérie
Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology,
Department of Civil Engineering, Algeria;
6YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea;
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia;
Interdisciplinary Research Center for Construction and Building Materials, KFUPM, Dhahran, Saudi Arabia;
Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan

Abstract
Structural performance of a new type of lightweight steel-timber composite (STC) beam has been investigated by conducting four-point bending tests on 21 specimens. This paper presents key findings on its structural performance parameters such as failure modes, load-deflection response, load-slip response, load-strain response, and the ultimate bending capacity by grouping 21 specimens into 7 subgroups based on various geometric characteristics. In the proposed STC beams, glulam slabs were connected to the steel beams using high-strength bolts, and the effect of different thickness and width of glulam slabs on the structural behaviour of STC beams were carefully investigated. In addition, the effective bending stiffness, deflection, and bending capacity of the STC beams were theoretically calculated based on elastic theory and compared with experimental values. For all considered specimens, timber slabs and steel beams showed good composite action. Increasing the thickness and width of the timber slabs can effectively limit the lateral deformation of the specimens, improve the bending capacity of the specimens, and provides a secant stiffness to the STC beams. It was observed that for the whole cross section of STC beams, the plane section assumption is not applicable, but the strains on timber and steel seemed to satisfy the plane section assumption individually. r (Gamma) method has been observed to better reflect the deformation capacity of STC beams. Analytical equations were derived to predict the elastic bending capacity of STC beams, and comparison between theoretical and experimental values showed good agreement.

Key Words
bending capacity; effective bending stiffness; four-point bending; glulam timber slab; light-weight beam; steel-timber composite (STC) beam

Address
Ruyuan Yang: College of Art & Design, Nanjing Tech University, Nanjing, China
Haitao Li and Youfu Sun: College of Civil Engineering, Nanjing Forestry University, Nanjing, China
Rodolfo Lorenzo: University College London, London WC1E 6BT, UK
Mahmud Ashraf: School of Engineering, Deakin University, Geelong Waurn Ponds, VIC 3216, Australia

Abstract
A railway bridge with slab track is subjected to end rotations because of the deflection of the girder during train operation. At the ends of a slab track, the end rotation of the bridge girder causes uplift deformation of the slab track, and leads to compressive stresses in the rail fasteners. In this study, a prototype bridge consisting of one span of a girder and one span of an abutment along with a slab track was constructed, and the uplift and compressive forces generated in the rail fastening system were experimentally analyzed. To effectively analyze the experimental results using a numerical method, a series of finite element analyses were performed considering the nonlinear nature of the rail fastening system. A comparison between the experimental and analytical results indicated that the higher the stiffness of the rail fastening system, the greater the uplift and compressive forces. In addition, a nonlinear model provided better correlation with the experimental results than a linear model. Therefore, when reviewing the serviceability of the rail fastening system at railway bridge ends, an adequate finite element model considering the uplift and compressive forces in the rail fastening system should be used.

Key Words
bridge end rotation; experimental study; nonlinear behavior; railway bridge deck end; rail fastening system; slab track

Address
Deokyong Sung: Department of Civil & Railroad Engineering, Daewon University College, 316 Daehak-ro, Jecheon,
Chung-Buk, 27135, Republic of Korea
Sukhoon Pyo: Department of Urban & Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST),
50 UNIST-gil, Ulju-gun, Ulsan, 44919, Republic of Korea
Seongkyu Chang: Department of Civil Engineering, Gwangju University, 277 Hyodeok-ro, Nam-gu, Gwangju, 61743, Republic of Korea

Abstract
The deflection of composite (cellular) beams is important for serviceability purposes. However, the available methods to predict the deflection are inaccurate. This research aims to propose a method for predicting the deflection with improved accuracy. The proposed deflection consists of contributions from overall flexural behavior and Vierendeel bending. In addition to the slip action, a reduction factor for computing the effective moment of inertia is investigated and used to compute the flexural deflection. The Vierendeel deformation was determined based on shear deflection of a virtual cantilever beam. No local composite action is conservatively assumed in the cantilever beam. Over 700 three-dimensional finite element (FE) models were simulated to investigate the reduction factor and limitations of the proposed method. The FE model was validated against 13 experimental load-deflection curves from the literature. The proposed method is suitable for predicting the deflection of composite cellular beams having the spacing ratio 1.35 or higher and the span ratio higher than 5. For such cases, the deflection estimate is from 0.90 to 1.05 times the FE deflection. The web-post deformation and the global shear deflection affect the prediction accuracy. In comparison to other methods, the proposed method is more accurate in predicting the deflection.

Key Words
cellular beam; composite; deflection; reduction factor; Vierendeel bending

Address
Hnin Wai Hlaing and Pattamad Panedpojaman: Department of Civil Engineering, Faculty of Engineering, Prince of Songkla University, Songkhla 90110, Thailand

Abstract
Safety monitoring and stability analysis of high slopes are essential for construction of concrete dam in precipitous gorges or mountainous areas. The estimate of slope stability is a difficult engineering shortcoming with a number of variables. Thereafter, a hybrid model of Support Vector Regression (SVR) and Teaching–learning-based optimization technique (TLBO) is proposed to develop the predicting function. TLBO was used in obtaining the best SRV factors to improve the prediction accuracy. Few essential factors, such as the installation height of instruments, classification of rock masses, modulus of elasticity, the complete measuring time cycle, the excavation height of slope, the start measuring time, and the actual excavation height after measurement are considered as the input parameter, but the slope displacement is regarded as output. The outcomes showed SRV-TLBO a reliable hybrid accurate prediction of slope stability, then it was effectively used to the left abutment slope of Jinping I hydropower station located in Yalongjiang concrete dam reservoir as a novel method for this purpose.

Key Words
reservoir bank; slope stability; SVR TLBO algorithm

Address
Guoqiang Zhang, Wenkai Feng and Hai Shao: State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, (Chengdu University of Technology),
Chengdu 610059, Sichuan, China
Mingtang Wu and Feng Ma: Zhejiang Huadong Construction Engineering Corporation Limited, Hangzhou 610059, Zhejiang, China

Abstract
To meet the demands of the sustainable development of construction, the combination of precast structures and recycled aggregate concrete made from construction and demolition waste is being promoted as a promising green construction technology. In this study, a new prefabricated member, a buckling-restrained steel plate shear wall with a cover plate made of recycled aggregate concrete (PBRW), was developed and experimentally studied. Eight specimens were tested to study the effect of the cover plate with different recycled aggregate substitution ratios and various bolt arrangements on the seismic behavior of this shear wall system. Based on the high-order buckling in the inner steel plate, a theoretical method was proposed to predict the shear resistance of PBRWs. The test results indicated that the PBRWs exhibited high shear strength, an adequate initial stiffness, a favorable energy absorption capacity, and a stable hysteresis curve. A full replacement of recycled aggregate with natural aggregate had almost no adverse impact on the seismic behavior of the PBRWs. The wall with an insufficient number of bolts (bolt arrangement of 3x2) imposed weaker lateral constraints on the inner plate, resulting in a reduction in the seismic behavior.

Key Words
buckling-restrained steel plate shear walls; high-order buckling analyses; recycled aggregate concrete; seismic behavior; shear resistance

Address
Muwang Wei: School of Civil Engineering and Architecture, Wuyi University,385 Baihua road, Wuyishang, Peoples

Abstract
Multi-order tensegrity structures are an attractive form of compliant deployable structures. An efficient numerical form-finding method is proposed for multi-stable tensegrity structures in this paper. The current method first analyze the force density matrix for sets of more feasible force densities that satisfy the non-degeneracy conditions. Then, based on symmetrical grouping of elements, a genetic algorithm is used to minimize the eigenvalues; as a result, multiple orders of equilibrium can be found. For the investigation, two symmetric tensegrity structures are analyzed using the currently proposed method, and the method's applicability and accuracy have been examined.

Key Words
grouping elements; force density; form-finding, multi-order; non-degeneracy condition

Address
Xinyu Wang and Jianguo Cai: Key Laboratory of C& PC Structures of Ministry of Education, Southeast University, Nanjing, China
Daniel Sang-hoon Lee: 3The Royal Danish Academy of Fine Arts, School of Architecture, School of Architecture, Institute of Technology
Yixiang Xu: School of Aerospace, UNNC, University of Nottingham Ningbo China
Jian Feng: Key Laboratory of C& PC Structures of Ministry of Education, Southeast University, Nanjing, China;
National Prestress Engineering Research Center, Southeast University, Nanjing, China

Abstract
In the present research, a novel analytical approach was developed to predict the bearing chord stiffness and the damage initiation bearing-load of single-lap composite bolted joints under medium strain rate loading. First, the elastic moduli, Poisson's ratio, and strength of a unidirectional composite ply at an arbitrary strain rate were predicted by available micromechanical equations. Then, the bearing chord stiffness of the joint at any arbitrary strain rate was predicted. For this purpose, the available spring-based model was modified. The strain-rate-dependent damage initiation bearing-load of the joint was predicted by using the moduli and the stress concentration factor of a pin-loaded unidirectional ply. Four types of single-lap joints with [-45/0/+45/90]s and [90/-452/+45]s layups with and without carbon nanofibers were tested at the strain rates of 0.0048 s-1, 0.36 s-1, and 0.89 s-1. The results of experiments showed that mechanical properties of single-lap composite bolted joints increased with increasing the strain rate. Also, employing carbon nanofibers has a significant effect on the mechanical properties of the joints. The predicted results in comparison with the conducted experimental data show good agreements.

Key Words
analytical approach; bearing chord stiffness; damage initiation bearing-load; experiment single-lap single-bolt composite joint; strain-rate

Address
Alireza Shamaei-Kashani and Mahmood M. Shokrieh: Department of Mechanical Engineering, Composites Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, Iran University of Science and Technology, Narmak, Tehran, 16846-13114, Iran

Abstract
At present, researchers mainly focused on the vortex-induced vibration (VIV) of the double-side I-shaped girder, while there are only a few literatures focused on the VIV of the bluff double-side box girder, especially the study on the synchronous pressure- and vibration- measured test for the bluff double-side box girder has not been reported. Therefore, in this study, the vibration-measured test, the Numerical Wind Tunnel Simulation, and the synchronous pressure- and vibration- measured test were conducted to study the VIV mechanism of the bluff double-side box girder. Firstly, a section model of the bluff double-side box girder was designed, and the vibration-measured test was conducted to study the influence of mass ratio, damping ratio, and aerodynamic countermeasures on the VIV of the bluff double-side box girder. Secondly, the Numerical Wind Tunnel Simulation was conducted to simulate the vorticity evolution of the bluff double-side box girder, which was used to help analyze the results of the synchronous pressure- and vibration- measured test. Finally, the synchronous pressure- and vibration- measured test was conducted to investigate the wind pressure distribution and aerodynamic forces on the surface of the double-side box girder, which was then used to study the VIV mechanism of the bluff double-side box girder by combining the simulated vorticity evolutions. So, when the VIV of the double-side box girder occurs, it is found that: there is a significant difference in the mean and fluctuating wind pressure between the upper and lower surfaces; moreover, at the leading and trailing edges, the aerodynamic forces contribute greatly to the VIV, the correlation between the aerodynamic forces and the vortex-induced aerodynamic forces is positive, and with the increase of this coefficient, it will lead to the more significant VIV.

Key Words
aerodynamic countermeasure; bluff double-side box section; numerical wind tunnel simulation; synchronous pressure- and vibration- measured test; vortex-induced vibration

Address
Yu Li, Feng Wang and Jia-wu Li: School of Highway, Chang'an University, Xi'an 710064, China
Chen Li: School of Architecture, Chang'an University, Xi'an 710061, China

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