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CONTENTS
Volume 78, Number 2, April25 2021
 

Abstract
This work focused on the novel numerical tool for the bending responses of carbon nanotube reinforced composites (CNTRC) beams. The higher order shear deformation beam theory (HSDT) is used to determine strain-displacement relationships. A new exponential function was introduced into the carbon nanotube (CNT) volume fraction equation to show the effect of the CNT distribution on the CNTRC beams through displacements and stresses. To determine the mechanical properties of CNTRCs, the rule of the mixture was employed by assuming that the single-walled carbon nanotubes (SWCNTs)are aligned and distributed in the matrix. The governing equations were derived by Hamilton's principle, and the mathematical models presented in this work are numerically provided to verify the accuracy of the present theory. The effects of aspect ratio (l/d), CNT volume fraction (Vcnt), and the order of exponent (n) on the displacement and stresses are presented and discussed in detail. Based on the analytical results. It turns out that the increase of the exponent degree (n) makes the X-beam stiffer and the exponential CNTs distribution plays an indispensable role to improve the mechanical properties of the CNTRC beams.

Key Words
nanotube; bending; shear deformation; volume fraction; beam

Address
Rachid Zerrouki: Faculty of Applied Sciences, Synthesis and Catalysis Laboratory LSCT, University of Tiaret, Algeria; University of Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algeria
Abdelkader Karas: Faculty of Applied Sciences, Synthesis and Catalysis Laboratory LSCT, University of Tiaret, Algeria; University of Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algeria
Mohamed Zidour: University of Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algeria; Laboratory of Geomatics and Sustainable Development, University of Tiaret, Algeria
Abdelmoumen Anis Bousahla: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria
Abdelouahed Tounsi: Material and Hydrology Laboratory, Civil Engineering Department, Faculty of Technology, University of SidiBel Abbes, 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
Fouad Bourada: Material and Hydrology Laboratory, Civil Engineering Department, Faculty of Technology, University of SidiBel Abbes, Algeria; Departement des Sciences et de la Technologie, Universite de Tissemsilt, BP 38004 Ben Hamouda, Algerie
Abdeldjebbar Tounsi: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria; Material and Hydrology Laboratory, Civil Engineering Department, Faculty of Technology, University of SidiBel Abbes, Algeria
Kouider Halim Benrahou: Material and Hydrology Laboratory, Civil Engineering Department, Faculty of Technology, University of SidiBel Abbes, Algeria
S.R. Mahmoud: GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia

Abstract
In this paper, the effects of Tuned Mass dampers (TMDs) on the reduction of the vertical vibrations of a real horizontally curved steel box-girder bridge due to different traffic loads are numerically investigated. The performance of TMDs to reduce the bridge vibrations can be affected by the parameters such as dynamic characteristics of TMDs, the location of TMDs, the speed and weight of vehicles. In the first part of this study, the effects of mass ratio, damping percentage, frequency ratio, and location of TMDs on the performance of TMDs to decrease vertical vibrations of different sections of bridge deck are evaluated. In the second part, the performance of TMD is investigated for different speeds and weights of traffic loads. Results show that the mass ratio of TMDs is the more effective parameter in reducing imposed vertical vibration in comparison with the damping ratio. Furthermore, it is found that TMD is very sensitive to its tuned frequency, i.e., with a little deviation from a suitable frequency, the expected performance of TMD significantly decreased. TMDs have a positive and considerable performance at certain vehicle speeds and this performance declines when the weight of traffic loads is increased. Besides, the results reveal that the highest impact of TMD on the reduction of the vertical vibrations is when free vibrations occur for the bridge deck. In that case, maximum reductions of 24% and 59% are reported in the vertical acceleration of the bridge deck for the forced and free vibration amplitudes, respectively. The maximum reduction of 13% is also obtained for the maximum displacement of the bridge deck. The results are mainly related to the resonance condition.

Key Words
tuned mass damper; horizontally curved bridges; steel box-girders; traffic loads; vehicles; vertical vibrations

Address
Elyas Bayat: Department of Civil, Chemical and Environmental Engineering, Genoa University, Genoa, Italy
Meysam Bayat: Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran
Raheb Hafezzadeh: Department of Engineering and Architecture, Parma University, Parma, Italy

Abstract
In this study, continuous contact problem in the functionally graded (FG) layer loaded with a FG flat punch resting on the elastic semi-infinite plane was analyzed by the finite element method (FEM). It was assumed that the shear modulus and density of the layer and punch varied according to exponentially throughout their depth. FG layer's weight was included to the problem and additionally all surfaces were considered as frictionless. Analysis of FG materials was performed with a special macro which was added to the ANSYS program. Firstly, the shear modulus of the punch was considered to be very rigid and the results of initial separation load (tcr) and distance (xcr) were compared with the analytical solution. Afterwards, results obtained from the contact analysis made according to the inhomogeneity parameters (B, r) between FG punch-FG layer which had been unprecedented in the literature were discussed. As a result, FG punch-FG layer which had been unprecedented in the literature were discussed. As a result, FG punch's stress values at the punch edges where stress accumulations occurred were found to be smaller than the rigid punch. The security of the structure, longer life of the material and ease of production are directly related to the reduction of the stress values. The results obtained in this study are important in this respect. Also this work is the first study that investigates the effect of FG punch on the FG layer.

Key Words
contact mechanics; elasticity; finite element method; functionally graded layer

Address
Alper Polat: Munzur University, Department of Civil Engineering, 62100, Tunceli, Turkey

Abstract
Dynamic compaction of Aluminum powder using gas detonation forming technique was investigated. The experiments were carried out on four different conditions of total pre-detonation pressure. The effects of the initial powder mass and grain particle size on the green density and strength of compacted specimens were investigated. The relationships between the mentioned powder design parameters and the final features of specimens were characterized using Response Surface Methodology (RSM). Artificial Neural Network (ANN) models using the Group Method of Data Handling (GMDH) algorithm were also developed to predict the green density and green strength of compacted specimens. Furthermore, the desirability function was employed for multi-objective optimization purposes. The obtained optimal solutions were verified with three new experiments and ANN models. The obtained experimental results corresponding to the best optimal setting with the desirability of 1 are 2714 kg m3 and 21.5 MPa for the green density and green strength, respectively, which are very close to the predicted values.

Key Words
aluminum powder; artificial neural network; high-velocity compaction; modelling; optimization; response surface methodology

Address
Tohid Mirzababaie Mostofi: Faculty of Mechanical Engineering, University of Eyvanekey, Eyvanekey, Iran
Mostafa Sayah-Badkhor: Faculty of Mechanical Engineering, University of Eyvanekey, Eyvanekey, Iran
Mohammad Rezasefat: Faculty of Mechanical Engineering, University of Eyvanekey, Eyvanekey, Iran
Hashem Babaei: Faculty of Mechanical Engineering, University of Guilan, Rasht, Iran
Togay Ozbakkaloglu: Ingram School of Engineering, Texas State University, San Marcos, TX 78666, USA

Abstract
Track-bridge interaction has become an essential part in the design of bridges and rails in terms of modern railways. As a unique ballastless slab track, the longitudinal continuous slab track (LCST) or referred to as the China railway track system Type-II (CRTS II) slab track, demonstrates a complex force mechanism. Therefore, a comprehensive track-bridge interaction study between multi-span simply supported beam bridges and the LCST is presented in this work. In specific, we have developed an integrated finite element model to investigate the overall interaction effects of the LCST-bridge system subjected to the actions of temperature changes, traffic loads, and braking forces. In that place, the deformation patterns of the track and bridge, and the distributions of longitudinal forces and the interfacial shear stress are studied. Our results show that the additional rail stress has been reduced under various loads and the rail's deformation has become much smoother after the transition of the two continuous structural layers of the LCST. However, the influence of the temperature difference of bridges is significant and cannot be ignored as this action can bend the bridge like the traffic load. The uniform temperature change causes the tensile stress of the concrete track structure and further induce cracks in them. Additionally, the influences of the friction coefficient of the sliding layer and the interfacial bond characteristics on the LCST's performance are discussed. The systematic study presented in this work may have some potential impacts on the understanding of the overall mechanical behavior of the LCSTbridge system.

Key Words
high-speed railway; ballastless track; CRTS II slab track; finite element analysis; temperature effect, longitudinal force

Address
Miao Su: School of Civil Engineering, Changsha University of Science and Technology, Changsha 410114, Hunan, China;
Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA
Yiyun Yang: School of Civil Engineering, Changsha University of Science and Technology, Changsha 410114, Hunan, China
Rensheng Pan: School of Civil Engineering, Changsha University of Science and Technology, Changsha 410114, Hunan, China

Abstract
Due to the increasing environmental pollution caused by scrap tires, a solution is being sought to recycle and use them in a field of civil engineering, i.e., construction. This paper will provide a brief overview of previous researches that give detailed information on the advantages and disadvantages, considering the microstructural and mechanical characteristics of self-compacting concrete, when waste tire rubber as an aggregate is added. With this aim, a database of 144 different mixtures of self-compacting concrete with partial substitute of natural aggregate with recycled tire rubber (self-compacting rubberized concrete, SCRC) provided by various researchers was created. In this study we show that Gaussian process regression (GPR) modelling is an appropriate method for predicting compressive strength of SCC with recycled tire rubber particles and is in accordance with the results displayed by SEM images.

Key Words
self-compacting concrete; compressive strength; recycled rubber; Gaussian process regression (GPR) model

Address
Marijana Hadzima-Nyarko: Faculty of Civil Engineering and Architecture Osijek, Josip Juraj Strossmayer University of Osijek, Vladimira Preloga 3, 31000 Osijek, Croatia
Karlo E. Nyarko: Faculty of Electrical Engineering, Computer Science and Information Technology Osijek, Josip Juraj Strossmayer University of Osijek, Kneza Trpimira 2b, 31000 Osijek, Croatia
Daniela Djikanovic: Institute for Multidisciplinary Research, University of Belgrade, Kneza Višeslava 1, Belgrade, Serbia
Goran Brankovic: Institute for Multidisciplinary Research, University of Belgrade, Kneza Višeslava 1, Belgrade, Serbia

Abstract
This paper harnesses a micropolar thermoelastic medium consisting of voids to scrutinize the impacts of a magnetic field on it. To assess the problem, the three-phase-lag model (3PHL) has been employed and the analytical expressions of various variables under consideration have been derived using normal model analysis. The paper presents a graphical illustration of the material's stress, temperature, and dimensionless displacement. It has also been ensured that the predictions associated with results by different theories are not neglected instead; they are used to carry out appropriate comparisons in scenarios where the magnetic field is present as well as absent. The numerical results indicate that the magnetic field and the phase-lag of heat flux play a vital role in determining the distribution of field quantities. Thus, the investigation helped derive various interesting cases.

Key Words
micropolar; thermoelasticity; magnetic field; three-phase-lag; voids

Address
Amnah M. Alharbi: Department of Mathematics, College of Science, Taif Univeristy, P.O. Box 11099, Taif, 21944, Saudi Arabia
Mohamed I.A. Othman: Department of Mathematics, Faculty of Science, Zagazig University, P.O. Box 44519, Zagazig, Egypt
Al-Anoud M. Kh. Al-Autabi: Department of Mathematics, College of Science, Taif Univeristy, P.O. Box 11099, Taif, 21944, Saudi Arabia

Abstract
In the present paper, an analytical model is proposed to determine the flexural and shear strength of normal and high-strength reinforced concrete beams with longitudinal bars, in the presence of transverse stirrups. The model is based on evaluation of the resistance contribution due to beam and arch actions including interaction with stirrups. For the resistance contribution of the main bars in tension the residual bond adherence of steel bars, including the effect of stirrups and the crack spacing of R.C. beams, is considered. The compressive strength of the compressed arch is also verified by taking into account the biaxial state of stresses. The model was verified on the basis of experimental data available in the literature and it is able to include the following variables in the resistance provision: - geometrical percentage of steel bars; - depth-to-shear span ratio; - resistance of materials; - crack spacing; - tensile stress in main bars; - residual bond resistance including the presence of stirrups;- size effects. Finally, some of the more recent analytical expressions able to predict shear and flexural resistance of concrete beams are mentioned and a comparison is made with experimental data.

Key Words
shear-moment interaction; high-strength concrete; shear resistance; flexural strength

Address
Giuseppe Campione: Department of Engineering, University of Palermo, Viale delle Scienze Ed.8, 90128, Palermo, Italy

Abstract
For engineering, there are two major challenges in reliability analysis. First, to ensure the accuracy of simulation results, mechanical products are usually defined implicitly by complex numerical models that require time-consuming. Second, the mechanical products are fortunately designed with a large safety margin, which leads to a low failure probability. This paper proposes an efficient and high-precision adaptive active learning algorithm based on the Kriging surrogate model to deal with the problems with low failure probability and time-consuming numerical models. In order to solve the problem with multiple failure regions, the adaptive kernel-density estimation is introduced and improved. Meanwhile, a new criterion for selecting points based on the current Kriging model is proposed to improve the computational efficiency. The criterion for choosing the best sampling points considers not only the probability of misjudging the sign of the response value at a point by the Kriging model but also the distribution information at that point. In order to prevent the distance between the selected training points from too close, the correlation between training points is limited to avoid information redundancy and improve the computation efficiency of the algorithm. Finally, the efficiency and accuracy of the proposed method are verified compared with other algorithms through two academic examples and one engineering application.

Key Words
structural reliability; the Kriging model; low failure probability; adaptive kernel-density estimation

Address
Runan Cao, Zhili Sun, Jian Wang and Fanyi Guo: School of Mechanical Engineering and Automation, Northeastern University, Wenhua Road, Heping District, Shenyang110819, Liaoning, People's Republic of China

Abstract
International seismic codes stipulate that adjacent buildings should be separated by a specified minimum distance, otherwise the pounding effect should be considered in the design. Recent researches proposed an alternative method (Double Difference Combination Rule) to estimate seismic gap between structures, as this method considers the cross relation of adjacent buildings behavior during earthquakes. Four different criteria were used to calculate the minimum separation distance using this method and results are compared to the international codes for five separation cases. These cases used four case study buildings classified by different heights, lateral load resisting systems and fundamental periods of vibrations to assess the consistency in results for the alternative methods. Non-linear analysis was performed to calculate the inelastic displacements of the four buildings, and the results were used to evaluate the relation between elastic and inelastic displacements due to the ductility of structural elements resisting seismic loads. A verification analysis was conducted to guarantee that the separation distance calculated is sufficient to avoid pounding. Results shows that the use of two out of the four studied methods yields separation distances smaller than that calculated by the code specified equations without under-estimating the minimum separation distance required to avoid pounding.

Key Words
earthquake resistant design; pounding; separation distance; double difference combination rule; correlation factor; inelastic displacement; non-linear analysis

Address
Manar M. Hussein, Ahmed A. Mostafa and Walid A. Attia: Department of Structural Engineering, Faculty of Engineering, Cairo University, Giza, Egypt

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