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CONTENTS
Volume 40, Number 2, July25 2021
 


Abstract
This paper constitutes an attempt to explore the influence of porosity on free vibration analysis of functionally graded (FG) beams with different boundary conditions using different efficient analytical and numerical approaches. The material properties of open-cell FG porous beams are estimated using a modified power-law with two different types of porosity distributions through the thickness direction of the FG beam namely even and non-even distributions. Hamilton's principle is used to derive the equations of motion of the FG porous beam with high-order shear deformation theory. The state-space approach is utilized to solve the problem in the analytical solution section. In addition to the theoretical solution, a simulation based on a displacement type of finite element method (FEM) was utilized to verify the analytical solution. For this purpose, three-dimensional shell beams were modeled using ABAQUS for the solution of the vibration problem of the FG porous beam. Furthermore, the Artificial Neural Networks (ANNs) technique is used to predict the effects of porosity distributions, porosity coefficient, slenderness ratio and boundary conditions on natural frequency variations of porous FG beam. The ANNs technique allows for an investigation of the effects of various parameters, including beam characteristics, material properties, geometric details and porosity distributions.

Key Words
finite element method; free vibration; functionally graded material (FGM); high-order theory; porosity; artificial neural networks

Address
Emrah Madenci and Yasin Onuralp Ozkilic: Necmettin Erbakan University, Department of Civil Engineering, 42140 Konya, Turkey

Abstract
The structural damage or collapse caused by weak-story failure mechanisms poses a great threat to the safety of human life and property under strong earthquakes. Many researchers have attempted to transform this unexpected failure mechanism into the desired overall failure mechanism by installing various energy dissipation devices on unsafe structures. This paper introduced a lattice-shaped friction device (LSFD), which is a friction device with hardening postyielding stiffness, into a steel frame with a weak-story failure mechanism. Then, shaking table tests of a three types of two-story steel frames—a frame with LSFDs, a frame with traditional friction brace dampers (FBDs), and a bare frame—were carried out. The seismic responses of the hardening postyielding stiffness of the LSFD on the weak-story failure mechanism of the frame were emphatically studied. The results showed that there was little difference in the seismic responses between the two damped structures under moderate and weak earthquakes. The distribution of maximum story drift for the structure with LSFDs was more uniform, which effectively suppressed the weak-story failure under strong earthquakes, whereas the structure with FBDs had serious deformation concentrations. The numerical simulation results of the structure with LSFDs in the shaking table test showed that the simplified model results were basically consistent with the experimental results. Hence, this model could be used to analyze the seismic performance of damped structures with LSFDs.

Key Words
dynamic load; energy dissipation; hardening postyielding stiffness; shaking table test; weak-story failure mechanism

Address
Li-Hua Zhu: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning Province 116024 China;
College of Civil Engineering, Hebei University of Engineering, Handan, Hebei Province 056038 China
Gang Li and Zhi-Qian Dong: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning Province 116024 China


Abstract
Welding defects negatively affect the safety of steel structures. In fire, the steel connections with welding defects would fracture prematurely that cause the structure lose their fire resistance. However, the knowledge of effects of welding defects on welding connections at elevated temperature are still limit. This paper conducted steady-state tensile tests on butt welded specimens with artificial defects to investigate the effect of defects on the mechanical properties of butt welding at high temperatures. These effects on the evolution law of stress and strain, fracture strengths and extension abilities were discussed. The results show that the stress concentration caused by the defects in the welding zone reduced the yield strengths of the weldments at high-temperature, and the stress concentration induced brittle fracture occurring at the welding zone at high temperature with low levels and produced different failure modes. The extension abilities of the weldments at different temperatures were influenced by the defect levels significantly.

Key Words
butt welding; evolution law; high temperature; stress concentration; welding defect

Address
Min Yan,Yi Liu and Xiangren Wang: School of Mechanics & Civil Engineering, China University of Mining and Technology, Xu Zhou, Jiangsu 221116, China
Zhen Guo: School of Mechanics & Civil Engineering, China University of Mining and Technology, Xu Zhou, Jiangsu 221116, China; Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering, China University of Mining & Technology,
Xu Zhou, Jiangsu 221116, China
Chenfeng Li: College of Shipbuilding Engineering, Harbin Engineering University, Harbin, Heilongjiang 150001, China



Abstract
The present study is dealing with a geometrically nonlinear model of the suspended cable subjected to multi-frequency excitations. In particular, two of the super, sub-harmonic, and combination resonances are excited simultaneously here. The nonlinear integro-differential equations of the suspended cable are introduced, together with the Galerkin method, to obtain a reduced-order model, whose responses are investigated by solving the reduced ordinary differential equations. Then, the obtained single-mode discretization equations are solved using the method of multiple scales in the frequency regions of three simultaneous resonant cases, with the stability characteristics determined. Effects of parameters on resonance characteristics are carried out by investigating several numerical examples. Numerical results demonstrate that the two-frequency excitation has significant influences on the dynamical behaviors of the nonlinear system. Each harmonic excitation component's contribution to the overall resonant responses is mainly dependent on its excitation amplitude. The stable steady-state solutions are confirmed by using numerical integration, and the number of steady-state solutions varies from one to seven as to different parameters of the system in simultaneous resonances. Besides, it is of great significance to include the effects of excitation phase differences on nonlinear vibration characteristics.

Key Words
method of multiple scales; parameter analysis; super/sub-harmonic resonance; suspended cable; vibration behavior

Address
Yaobing Zhao: College of Civil Engineering, Huaqiao University, Xiamen, Fujian 361021, People's Republic of China; Fujian Provincial Key Laboratory of Intelligent Infrastructure and Monitoring, Huaqiao University,
Xiamen, Fujian 361021, People's Republic of China


Abstract
Steel structures exposed to general atmosphere for a long time are highly susceptible to corrosion damage, which would lead to the degradation of service performance of the components and even structures. This article focuses on the effect of corrosion on the seismic performance of steel column. The accelerated corrosion tests in general atmosphere were conducted on 7 H-shaped steel columns and 20 steel plates. Then the obtained plate specimens were subjected to monotonic tensile tests and cyclic loading tests, and the steel columns were subjected to pseudo-static tests, respectively, to study the effects of corrosion on their mechanical properties and seismic performance. Then, a simplified three-dimensional finite element model (FEM) capable of accurately simulating the hysteretic response of corroded steel columns under low-cycle loading was established. Experimental results indicated that the yield strength, tensile strength, elastic modulus and peak strain of corroded steel plate decreased linearly with the proposed corrosion damage parameter Dn, and the energy dissipations under low-cycle loading were significantly reduced. There is a correlation between the cyclic hardening parameters of corroded steel and the yield-tensile strength difference (SD), and then a simplified formula was proposed. Corrosion could result in the premature entrance of each loading stage of corroded columns and the deterioration of buckling deformation range, bearing capacity and energy dissipation, etc. In addition, a larger axial compression ratio (CR) would further accelerate the failure process of corroded columns. The parametric finite element analysis (FEA) indicated that greater damage was found for steel columns with non-uniform corrosion, and hysteretic performance degraded more significantly when corrosion distributed at flanges or foot zone.

Key Words
corrosion; cyclic constitutive relation; general atmosphere; seismic performance; steel column

Address
Youde Wang, Tao Shi, Biao Nie and Shanhua Xu: 1School of Civil Engineering, Xi'an University of Architecture & Technology,
No.13, middle section of Yanta Road, Beilin District, Xi'an, China
Hao Wang: Central Research Institute of Building and Construction Co. Ltd. MCC Group,
No.33, Xitucheng Road, Haidian District, Beijing, China



Abstract
In this research, thermal and electrical effects on dynamic response of a porous nano-sized plate modeled by a nonlocal higher-order refined plate model have been explored in detail. A hyperbolic shear stain function has been used. The porous material considered in this research may have uniform or non-uniform porosity distribution across the cross section. Stain gradient effects have also been considered for more accurate modeling of the scale-dependent plate. Hamilton's rule has been employed for establishing the governing equations. Derived findings by differential quadrature (DQ) method have been validated with those represented in previous researches. The effects of thermal environment, electrical environment, nonlocal scale, and porous material on dynamic behaviors of foam-based nanoplate have been explored.

Key Words
dynamic response; electric voltage; foam; piezoelectric plate; thermal environment

Address
Ridha A. Ahmed, Basima Salman Khalaf,
Kareem Mohsen Raheef, Raad M. Fenjan and Nadhim M. Faleh: Al-Mustansiriah University, Engineering Collage P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq


Abstract
In order to accurately grasp the mechanical behavior of the composite beam structure and achieve its refined analysis. In this paper, the stiffness matrix of a new type of spatial grid element is derived using the principle of energy variation. Based on the spatial grid element, a finite element analysis program is written using MATLAB software. A new type of spatial grid element analysis method that can be used for the overall force analysis of composite beam structures as well as the local refined analysis of the structure is proposed. In addition, the internal force, stress and displacement of each part of the composite beam can also be directly obtained. In order to verify the accuracy and reliability of the spatial grid analysis element proposed in this paper. The composite beam in the existing references are used as the analysis object, and the analysis result of the spatial grid element is compared with the references result. The research results show that the analysis results of spatial grid elements have high accuracy and can realize the refined analysis of composite beams.

Key Words
composite beam; energy variational method; refined analysis space grillage element; stiffness matrix

Address
Pengzhen Lu, Dengguo Li, Simin Huang and Yijie Zhang: College of Civil Engineering, Zhejiang University of Technology, Hangzhou 310023, China
Ying Wu: Jiaxing Nanhu University, Jiaxing 314001, China


Abstract
This study was conducted to present a new technique to increase the capacity of reinforced concrete beams with insufficient shear reinforcement. Four beam specimens at 1/2 scale were produced. One of these beams was used for reference, while the other three were strengthened using different methods. The strengthening methods were performed using Mechanical stitches (MS), Glass fiber reinforced polymer (GFRP), and a hybrid of the two (GFRP and MS). In the experiments, the reference beam (E0), the MS-strengthened beam (E1), the GFRP-strengthened beam (E2), and the GFRP+MS-strengthened (E3) beam were tested under vertical load. Following the experiment, vertical load-bearing capacity, ductility value, initial stiffness value, and energy dissipation capacity were calculated for each beam. Afterward, extensive micro and macro damage analyses were performed. In the experiment, the E0 specimen resulted in a failure mode with direct shear damage. The strengthened E1 and E2 beams showed a typical bending behavior. The vertical load-bearing capacity of the E1 and E2 beams increased by 16.8% and 18.1%, respectively, compared to E0. The load-bearing capacity of the newly proposed technique, the hybrid E3 beam, was increased by 19.2%, although it failed with shear damage. Thus, this study has clearly demonstrated that beams with insufficient shear reinforcement can be strengthened using single-layer GFRP (E2). Considering its cost-efficiency compared to other composite materials, it has been suggested that GFRP should be used more widely in the market. In addition, it is reccommended that future studies can use the proposed E1 strengthening for beams weak against shear. The experiments revealed the most appropriate strengthening method for shear beams to be E1>E2>E3 in terms of performance/cost. Finally, the results suggest that the proposed hybrid strengthening (E3) can be turned to a ductile behavior through further experiments with different configurations.

Key Words
GFRP composite; glass fabric; hybrid system; mechanical stitches; shear beam; strengthening

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

Abstract
Recently, a new generation of cold-formed steel (CFS) channel section with edge-stiffened web holes has been developed by industry in New Zealand. However, no research has been reported in the literature to investigate the axial capacity of back-to-back channels with edge-stiffened web holes. This paper presents a total of 73 new results comprising 29 compression tests and 44 finite element analyses (FEA) on axial capacity of such back-to-back CFS channels. The results show that for back-to-back channels with seven edge-stiffened holes, the axial capacity increased by 19.2%, compared to plain channels without web holes. A non-linear finite element (FE) model was developed and validated against the test results. The validated FE model was used to conduct a parametric study involving 44 FE models. Finely, the tests results were compared with the design strengths calculated from the AISI and AS/NZ standards and from the proposed design equations of Moen and Schafer. From the comparison results, it was found that the AISI and AS/NZ design strengths are only 9% conservative to the test results for plain channels without web holes. While Moen and Schafer equations are conservative by 13% and 47% for axial capacity of CFS back-to-back channels with un-stiffened and edge-stiffened web holes, respectively.

Key Words
back-to-back channels; cold-formed steel; compression tests; edge-stiffened holes; finite element modelling

Address
Yaohui Chi: College of Harbour and Coastal Engineering, Jimei University, China
Krishanu Roy, Boshan Chen, Zhiyuan Fang and James B.P. Lim: Department of Civil and Environmental Engineering, The University of Auckland, New Zealand
Asraf Uzzaman: School of Computing, Engineering and Physical Sciences, University of the West of Scotland, United Kingdom
G. Beulah Gnana Ananthi: Division of Structural Engineering, College of Engineering Guindy Campus, Anna University, Chennai, India


Abstract
In this study, a simple and efficient higher order shear deformation theory is formulated for free vibration analysis of functionally graded (FG) shells. By introducing the undetermined integral terms in displacement field, the number of generated unknowns and their related governing equations is reduced in contrast to previously published theories, and therefore the differentiability of governing motion equations is decreased, this motivation turns the present theory simpler and easily exploited for functionally graded shell mechanical simulation. Both strains and stress rise through the thickness coordinate as function of hyperbolical distribution. The Hamilton's principle is deployed to derive the governing and motion equations. Closed form solutions are obtained for free vibration problems using Navier's method. Furthermore, detailed comparisons with other shear deformation theories are presented to illustrate the efficiency and accuracy of the developed theory. From this perspective, various perceptions on the impact of some important parameters such as material distribution, geometrical configuration, thickness and curvature ratios are studied and discussed. The non-trivial aspects in predicting the free vibration responses of FG shells are also pointed out.

Key Words
analytical solutions; free vibration; functionally graded (FG) shells; shear deformation shell theory

Address
Zakaria Belabed: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
Department of Technology, Institute of Science and Technology, Naama University Center, BP 66, 45000 Naama, Algeria
Mahmoud M. Selim: Department of Mathematics, Al-Aflaj College of Science and Humanities, Prince Sattam bin Abdulaziz University, Al-Aflaj 710-11912, Saudi Arabia
Omar Slimani: FIMAS Laboratory, Department of Civil Engineering, Faculty of Technology, Tahri Mohamed University, 08000 Bechar, Algeria
Noureddine Taibi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
YFL (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
Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38000, Faisalabad, Pakistan




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