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CONTENTS
Volume 78, Number 1, April10 2021
 


Abstract
In this study, the porothermoelastic problem with the effect of the magnetic field and initial stress was investigated. We applied normal mode analysis to solve the resulting non-dimensional coupled equations. Numerical results for the displacements, temperature distribution, pore pressure, stresses, induced electric field and induced magnetic field distributions are presented graphically and discussed. The medium deformed because of thermal shock and due to the application of the magnetic field, there result an induced magnetic and an induced electric field in the medium. Numerical analyses are given graphically on the square (2D) and cubic (3D) domains to illustrate the effects of the porosity parameter, magnetic field and initial stress parameter on the physical variables.

Key Words
porothermoelasticity; magnetic field; electric field; initial stress; normal mode analysis

Address
Elsayed M. Abd-Elaziz: Ministry of Higher Education, Zagazig Higher Institute of Eng. & Tech., Zagazig, Egypt

Abstract
An investigation of the nonlinear thermal buckling behavior of a nano-sized beam constructed from intelligent materials called piezo-magnetic materials has been presented in this article. The nano-sized beam geometry has been considered based on two assumptions: an ideal straight beam and an imperfect beam. For incorporating nano-size impacts, the nano-sized beam formulation has been presented according to nonlocal elasticity. After establishing the governing equations based on classic beam theory and nonlocal elasticity, the nonlinear buckling path has been obtained via Galerkin's method together with an analytical trend. The dependency of buckling path to piezo-magnetic material composition, electro-magnetic fields and geometry imperfectness has been studied in detail.

Key Words
piezo-magnetic beam; geometry imperfection; thermal post-buckling; piezoelectric reinforcement; nonlocal elasticity

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

Abstract
In this paper, we established the generalized thermoelasticity phenomenon in an isotropic elastic medium considering the electromagnetic field, rotation and two-temperature. Three theories of generalized thermoelasticity have been applied: Lord-Shulman (one relaxation time), Green-Lindsay (two relaxation times), as well as the coupled theory. We discussed some particular cases in the context of the wave propagation phenomenon in thermoelasticity. From solving the fundamental equations, we arrived that there are three waves: P-, T- and SV-waves that we calculated their velocities. The boundary conditions for mechanical stress and Maxwell's stress and thermal insulated or isothermal have been applied to determine the amplitudes ratios (reflection coefficients) for P-, T - and SV waves. Some utilitarian aspects are obtained from the reflection coefficients, presented graphically, and the new conclusions have been presented. Comparisons are made for the results predicted by different theories (CT, LS, GL) in the absence and presence of the electro-magnetic field, rotation, as well as twotemperature on the reflection of generalized thermoelastic waves. The results obtained concluded that the external parameters as the angle of incidence, electromagnetic field, rotation as well as the theories parameters have strong effect on the phenomenon.

Key Words
electromagnetic field; reflection; rotation; P-wave; T-wave; SV-wave; two-temperature, relaxation times

Address
S.M. Abo-Dahab: Department of Mathematic, Qena Faculty of Science, South Valley University, Qena 83523, Egypt; Department of Computer Science, Faculty of Computers and Information, Luxor University, Egypt
Mohamed I.A. Othman: Department of Mathematic, Faculty of Science, Zagazig University, P.O. Box 44519, Zagazig, Egypt
Ohoud N.S. Alsebaey: Department of Mathematic, Faculty of Science, Taif University 888, Taif, Saudi Arabia

Abstract
To investigate numerically the effect of all parameters on the outcome of an aircraft impact into robust engineering structures like nuclear power plant containments is a tedious task. In order to reduce the problem to a manageable size, we propose a single dimensionless parameter, the damage potential, to characterize the main features of the impact. The damage potential, which is the ratio of the initial kinetic energy of the aircraft to the work required to crush it, enables us to find the crucial parameter settings that need to be modelled numerically in detail. We show in this paper that the damage potential is indeed the most important parameter of the impact that determines the time-dependent reaction force when either finite element (FE) modelling or the Riera model is applied. We find that parameters that do not alter the damage potential, like elasticity of the target, are of secondary importance and if parameters are altered in a way that the damage potential remains the same then the course of the impact remains similar. We show, however, that the maximum value of the reaction force can be higher in case of elastic targets than in case of rigid targets due to the vibration of the target. The difference between the Riera and FE model results is also found to depend on the damage potential.

Key Words
soft aircraft impact; finite element model; Riera model; dimensionless parameter; damage potential

Address
Lili E. Hlavicka-Laczak, Laszlo P. Kollar: Department of Structural Engineering, Budapest University of Technology and Economics, Műegyetem rkp. 3, H-1111, Budapest, Hungary
Gyorgy Karolyi: Institute of Nuclear Techniques, Budapest University of Technology and Economics, Műegyetem rkp. 3, H-1111, Budapest, Hungary

Abstract
Inelastic static pushover analysis has been used in the academic-research widely for seismic analysis of structures. Nowadays, the variety pushover analysis methods have been developed, including Modal pushover, Adaptive pushover, and Cyclic pushover, in which some weaknesses of the conventional pushover method have been rectified. In the conventional pushover analysis method, the effects of cumulative growth of cracks are not considered on the reduction of strength and stiffness of RC members that occur during earthquake or cyclic loading. Therefore, the Cyclic Pushover Analysis Method (CPA) has been proposed. This method is a powerful technique for seismic evaluation of regular reinforced concrete buildings in which the first mode of them is dominant. Since the bridges have different structures than buildings, their results cannot necessarily be attributed to bridges, and more research is needed. In this study, a cyclic pushover analysis with four loading protocols (suggested by valid references) by the Opensees software was conducted for seismic evaluation of two regular reinforce concrete bridges. The modeling method was validated with the comparison of the analytical and experimental results under both cyclic and dynamic loading. The failure mode of the piers was considered in two-mode of flexural failure and also a flexural-shear failure. Along with the cyclic analysis, conventional analysis has been studied. Also, the nonlinear incremental dynamic analysis (IDA) method has been used to examine and compare the results of pushover analyses. The time history of 20 far-field earthquake records was used to conduct IDA. After analysis, the base shear vs. displacement in the middle of the deck was drawn. The obtained results show that the cyclic pushover analysis method is able to evaluate an accurate seismic behavior of the reinforced concrete piers of the bridges. Based on the results, the cyclic pushover has proper convergence with IDA. Its accuracy was much higher than the conventional pushover, in which the bridge piers failed in flexural-shear mode. But, in the flexural failure mode, the results of each two pushover methods were close approximately. Besides, the cyclic pushover method with ACI loading protocol, and ATC-24 loading protocol, can provided more accurate results for evaluating the seismic investigation of the bridges, specially if the bridge piers are failed in flexural-shear failure mode.

Key Words
reinforce concrete bridges; pushover analysis; cyclic pushover analysis; incremental dynamic analysis

Address
Afshin Shafigh: Department of Civil Engineering, Bandar Abbas Branch, Islamic Azad University, Bandar Abbas, Iran
Hamid Reza Ahmadi: Department of Civil Engineering, Faculty of Engineering, University of Maragheh, Maragheh, P.O. Box 55136-553, Iran
Mahmoud Bayat: Department of Civil and Environmental Engineering, University of South Carolina, Columbia, SC, USA

Abstract
The determination of the damage index to reveal the performance level of a structure can constitute the seismic risk generalization approach based on the parametric analysis. This study implemented this concept to one kind of civil engineering structure that is the concrete gravity dam. Different cases of the structure exhibit their individual responses, which constitute different considerations. Therefore, this approach allows the parametric study of concrete as well as soil for evaluating the seismic nature in the generalized case. To ensure that the target algorithm applicable to most of the concrete gravity dams, a very simple procedure has been considered. In order to develop a correlated algorithm (by response surface methodology; RSM) between the ground motion and the structural property, randomized sampling was adopted through a stochastic method called half-fractional central composite design. The responses in the case of fluid-foundation-dam interaction (FFDI) make it more reliable by introducing the foundation as being bounded by infinite elements. To evaluate the seismic generalization of FFDI models, incremental dynamic analysis (IDA) was carried out under the impacts of various earthquake records, which have been selected from the Pacific Earthquake Engineering Research Center data. Here, the displacement-based damage indexed fragility curves have been generated to show the variation in the seismic pattern of the dam. The responses to the sensitivity analysis of the various parameters presented here are the most effective controlling factors for the concrete gravity dam. Finally, to establish the accuracy of the proposed approach, reliable verification was adopted in this study.

Key Words
seismic risk generalization; damage index; response surface methodology; fluid-foundation-dam interaction; fragility analysis; concrete gravity dams

Address
Tahmina T. Nahar: Department of Civil Engineering, Pabna University of Science and Technology, Pabna-6600, Bangladesh
Md M. Rahman: Department of Civil and Environmental Engineering, Kunsan National University, Gunsan-si, Republic of Korea
Dookie Kim: Department of Civil and Environmental Engineering, Kongju National University, Cheonan-si, Republic of Korea

Abstract
This work studies the behaviour of a steel portal frame selection under fire exposure, considering both span lengths and fire exposure times as variables. Such structures combine carbon steel (S275), fireproof micro-alloyed steel (FR), and coatings of intumescent paint with variable thicknesses, improving thereby the flame retardant behaviour of the steel structure. Thus, the main contribution of this study is the optimization of the portal frames by combining both steels, analysing the resulting costs influence on the final dimensions. Besides, the topological optimization of each steel component within the structure is also defined, in accordance with the following variables: weather conditions, span, paint thickness, and cost of steel. The results mainly confirmed that using both FR and S275 grades with intumescent painting is the Pareto optimum when considering performance, feasibility and costs of such portal frames widely used for industrial facilities.

Key Words
fire resistance steel; FR; metallic structure; intumescent paint; dimensioning method; structural optimization

Address
Harkaitz Garcia: Department of Mechanical Engineering, University of the Basque Country (UPV/EHU), 48940 Leioa Vizcaya, Spain
Jesus Cuadrado: Department of Mechanical Engineering, University of the Basque Country (UPV/EHU), 48940 Leioa Vizcaya, Spain
Maria V. Biezma: Department of Earth and Materials Science and Engineering, University of Cantabria, 39004 Santander, Spain
Inigo Calderon: Sustainable Construction Division, Tecnalia Research and Innovation, 20009 San Sebastian, Guipuzcoa, Spain

Abstract
Local school buildings are critical facilities that can provide shelter in disasters such as earthquakes, so they must be more resistant to seismic forces than other structures. In this study, a sensitivity analysis was conducted to determine which columns-as the most critical members in a reinforced concrete building-most urgently require seismic retrofitting. The sensitivity analysis was conducted using an optimization technique with the location of each column as a parameter. A numerical model was developed to simulate a realistic collapse mode through a three-dimensional dynamic analysis. Based on numerical analysis results, it was found that the columns positioned in the lower floors, such as the first floor and in the outer part of a building, urgently require retrofitting. For reinforcement of the RC columns, which has been proven for its performance in previous research, was applied. Through this study, the importance of appropriate retrofitting is demonstrated. Further, a method for determining the appropriate location for retrofitting-when retrofitting is not possible on the entire structure-is presented.

Key Words
sensitivity analysis; optimization; school building; RC column; seismic retrofitting

Address
Hyunsu Seo: Institute of Technology Team, Daon Co., LTD, 20, Nodae-gil, Hwasun-eup, Hwasun-gun, 58125, South Korea
Kyoungsub Park: Department of Civil Engineering, University fo Texas at Arlington, Arlington, TX76013, USA
Minho Kwon: Department of Civil Engineering, Gyeongsang National University, Jinju, 52828, South Korea
Jinsup Kim: Department of Civil Engineering, Gyeongsang National University, Jinju, 52828, South Korea

Abstract
Long span cross-rope suspension structure is an innovative structural system evolved from typical Cross-Rope Suspension (CRS) guyed tower, a type of supporting system with short span suspension cable supporting overhead power transmission lines. In mountainous areas, the span length of suspension cable was designed to be extended to hundreds or over one thousand meters, which is applicable for crossing deep valleys. Vortex Induced Vibration (VIV) of overhead power transmission lines was considered to be one of the major factors of its fatigue and service life. In this paper, VIV and its controlling by Stockbridge damper for long span CRS was discussed. Firstly, energy balance method and finite element method for assessing VIV of CRS were presented. An approach of establishing FE model of long span CRS structure with dampers was introduced. The effect of Stockbridge damper for overall vibration of CRS was compared in both theoretical and numerical approaches. Results indicated that vibration characteristics of conductor in long span CRS compared with traditional tower-line system. Secondly, analysis on long span CRS including Stockbridge damper showed additional dampers installed were essential for controlling maximum dynamic bending stresses of conductors at both ends. Moreover, factors, including configuration and mass of Stockbridge damper, span length of suspension cable and conductor and number of spans of conductor, were assessed for further discussion on VIV controlling of long span CRS.

Key Words
Cross-Rope Suspension; power transmission line; long span; Stockbridge damper; vortex induced vibration

Address
Xi Tu, Ye Wu, Zhengliang Li and Zhisong Wang: Key Laboratory of New Technology for Construction of Cities in Mountain Area, Chongqing University, Ministry of Education, Chongqing, China; College of Civil Engineering, Chongqing University, Chongqing, China

Abstract
In this work, a model of a functionally graded (FG) nanotube conveying fluid embedded in an elastic medium is developed based on the nonlocal strain gradient theory (NSGT) in conjunction with Euler-Bernoulli beam theory (EBT). The main objective of this research is to investigate the nonlinear vibration and stability analysis of fluid-conveying nanotubes. The governing equations of motion are derived by means of Hamiltonian principle. The analytical expressions of nonlinear frequencies and critical flow velocities for two different types of boundary conditions including pinned-pinned (P-P) and clamped-clamped (C-C) conditions are obtained by employing Galerkin method as well as Hamiltonian Approach (HA). Comparison of the obtained results with the published works show the acceptable accuracy of the current solutions. The effects of the power-law index, the nonlocal and material length scale parameters and the elastic medium on the stability and nonlinear responses of FG nanotubes are thoroughly investigated and discussed.

Key Words
nanotube; functionally graded material; nonlinear vibration; stability; conveying fluid

Address
Van-Hieu Dang: TNU - Thai Nguyen University of Technology, Thainguyen, Vietnam
Hamid M. Sedighi: Mechanical Engineering Department, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz 61357-43337, Iran; Drilling Center of Excellence and Research Center, Shahid Chamran University of Ahvaz, Ahvaz, 61357-43337, Iran
Do Quang Chan: University of Transport Technology, Hanoi, Vietnam
Omer Civalek: China Medical University, Taichung, Taiwan
Ahmed E. Abouelregal: Department of Mathematics, College of Science and Arts, Jouf University, Al-Qurayat, Saudi Arabia; Department of Mathematics, Faculty of Science, Mansoura University, Mansoura, Egypt


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