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CONTENTS
Volume 30, Number 4, October 2022
 


Abstract
This paper is concerned with exponential stability in mean square for stochastic static neutral neural networks with varying delays. By using Lyapunov functional method and with the help of stochastic analysis technique, the sufficient conditions to guarantee the exponential stability in mean square for the neural networks are obtained and some results of related literature are extended.

Key Words
exponential stability in mean square, static neutral neural networks, stochastic, varying delays

Address
Xiaoqi Sun: School of Mathematics and Statistics, Qingdao University, Qingdao 266071, China

Abstract
The static analysis of spinning functionally graded (FG) nanotube on the basis of the nonlocal strain gradient theory (NSGT) is presented. The high-order beam theory is employed for mathematical modeling of the tube structures according to the Sinusoidal shear deformation beam theory. The energy conservation principle is operated to generate the equations. The centrifugal force is assumed along the tube length due to the rotating of the tube, moreover, the nanotube is made of functionally graded material (FGM) composed of ceramic and metal phases along the tube radius direction. The generalized differential quadratic method (GDQM) is utilized to solve the formulations. Finally, the numerical results are discussed in detail to examine the impact of different relevant parameters on the bending the buckling behavior of the rotating nanotube.

Key Words
bending analysis, buckling behavior, functionally graded materials, nanotubes nonlocal strain gradient theory

Address
Liang Zhang: Institute of Intelligent Manufacturing, Guangdong Academy of Sciences, Guangzhou 510070, Guangdong, China
Tzu-Hsing Ko: Fujian Provincial Key Laboratory of Featured Materials in Biochemical Industry, College of Chemistry and Materials, Ningde Normal University, Ningde 352100, Fujian, China

Abstract
Two different types of rubber aggregates (40 mesh rubber powder and 1-4 mm rubber particles respectively) were devised to substitute fine aggregates at 10%, 15%, 20% and 30% by volume in self-compacting concrete to investigate their basic mechanical properties. The results show that with the increase of rubber content, the reduction of compressive strength, splitting tensile strength and static modulus of elasticity gradually increase, and energy dissipation performance gradually increase. The rubber addition significantly reduces brittleness and decelerates damaged process. Whilst, the effect of rubber particles is greater when they are finer. Considering the mechanical properties, the optimal rubber content is 10%. It is recommended that the rubber volume content in rubberized concrete (RC) should not be higher than 20%. In addition, a constitutive model under uniaxial compression was proposed basing on the strain equivalent principle of Lemaitre and the damage theory, which was in good agreement with the test curves.

Key Words
compression damage, constitutive model, mechanical properties, rubberized concrete (RC), self-compacting rubberized concrete (SCRC)

Address
Xiaojun Ke: Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education, School of Civil Engineering and Architecture, Guangxi University, Nanning 530004, PR China; Guangxi Key Laboratory of Disaster Prevention and Engineering Safety, Guangxi University, Nanning 530004, China
Wannian Xiang, Chunying Ye: Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education, School of Civil Engineering and Architecture, Guangxi University, Nanning 530004, PR China

Abstract
In this paper, frequency vibrations of double-walled carbon nanotubes (CNTs) has been investigated based upon nonlocal elastic theory. The inference of small scale is being perceived by establishing nonlocal Love shell model. The wave propagation approach has been operated to frame the governing equations as eigen value system. An innovational nonlocal model to examine the scale effect on vibrational behavior of armchair, zigzag and chiral of double-walled CNTs. An appropriate selection of material properties and nonlocal parameter has been considered. The influence of dimensionless nonlocal parameter has been studied in detail. The dominance of end condition via nonlocal parameter is explained graphically. The results generated furnish the evidence regarding applicability of nonlocal shell model and also verified by earlier published literature.

Key Words
dimensionless nonlocal parameter, double-walled CNTs, Love shell theory, vibration

Address
Muzamal Hussain, Sehar Asghar: Department of Mathematics, Govt. College University Faisalabad, 38040, Faisalabad, Pakistan
Mohamed Amine Khadimallah: Department of Civil Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, Al-Kharj, 11942, Saudi Arabia
Hamdi Ayed: Department of Civil Engineering, College of Engineering, King Khalid University, Abha, Kingdom of Saudi Arabia; Higher Institute of Transport and Logistics of Sousse, University Sousse, Tunisia
Sami Alghamdi: Electrical and Computer Engineering Department, King Abdulaziz University, Jeddah, Saudi Arabia; 2 Center of Nanotechnology, King Abdulaziz University, Jeddah, Saudi Arabia
Javed Khan Bhutto: Electrical Engineering Department, College of Engineering, King Khalid University, Abha 61421, Saudi Arabia
S.R. Mahmoud: GRC Department, Faculty of Applied Studies, King Abdulaziz University, Jeddah, Saudi Arabia
Abdelouahed Tounsi: FL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea; Department of Civil and Environmental Engineering, King Fahd University of Petroleum and Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
Due to the scarcity of extortionate experimental data, fatigue failure of the reinforced concrete (RC) element might be achieved economically adopting nonlinear finite element (FE) analysis as an alternative approach. However, conventional implicit dynamic analysis is expensive, quasi-static method overlooks interaction effects and inertia, direct cyclic analysis computes stabilized responses. Apart from this, explicit dynamic analysis may provide a numerical operating system for factual long-term responses. The study explores the fatigue behavior based on a simplified explicit dynamic solution employing nonlinear time domain analysis. Among fourteen RC beams, one beam is selected to validate under static loading, one under fatigue with the experimental study and other twelve to check the detail fatigue behavior. The SWOT (Strength, Weakness, Opportunities, Threats) analysis has been carried out to pinpoint the detail scenario in the adoption of numerical approach as an alternative to the experimental study. Excellent agreement of FE and experimental results is seen. The 3D nonlinear RC beam model at service fatigue limits is truthful to be used as an expedient contrivance to envisage the precise fatigue behavior. The simplified analysis approach for RC beam under fatigue offers savings in computation to predict responses providing acceptable accuracy rather than the complicated laboratory investigation. At higher frequency, the flexural failure occurs a bit earlier gradually compared to the repeated loading case of lower frequency. The deflection increases by 6%-10% at the end of first cycle for beams with increasing frequency of cyclic loading. However, at the end of fatigue loading, greater deflection occur earlier for higher load range because of more rapid stiffness degradation. For higher frequency, a slight boost in concrete compressive strains at an initial stage of loading has been seen indicating somewhat stepper increment. Stiffness degradation in larger loading cycle at same duration escalates the upsurge of the rate of strain in case of higher frequency.

Key Words
cracks, cyclic loading, damage behavior, explicit dynamic, fatigue, nonlinearities, RC beam, SWOT analysis

Address
A.B.M. Saiful Islam: Department of Civil & Construction Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University, 31451, Dammam, Saudi Arabia

Abstract
Based on the random cracking theory, the cylinder RVE model of reinforced concrete is established and the damage process is divided into three stages as the evolution of the cracks. The stress distribution along longitude direction of the concrete and the steel bar in the cylinder model are derived. The equivalent elastic modulus of the RVE are derived and the user-defined field variable subroutine (USDFLD) for the equivalent elastic modulus is well integrated into the ABAQUS. Regarding the tensile rebars and the concrete surrounding the rebars as the equivalent homogeneous transversely isotropic material, and the FEM analysis for the reinforced concrete beams is conducted with the USDFLD subroutine. Considering the concrete cracking and interfacial debonding, the macroscopic damage process of the reinforced concrete beam under four-point bending loading in the simulation. The volume fraction of rebar and the cracking degree are mainly discussed to reveal their influence on the macroperformance and they are calibrated with experimental results. Comparing with the bending experiment performed with 8 reinforced concrete beams, the bending stiffness of the second stage and the ultimate load simulated are in good agreement with the experimental values, which verifies the effectiveness and the accuracy of the improved finite element method for reinforced concrete beam.

Key Words
debonding, equivalent elastic modulus, four-point bending test, random cracking theory, reinforced concrete

Address
Yan-jun Chang, Li-yun Wan, De-kai Mo, Dan Hu and Shuang-bei Li: College of Civil and Architectural Engineering, Guangxi University, Nanning 530004, China; Guangxi Key Laboratory of Disaster Prevention and Engineering Safety, Nanning 530004, China; Key Laboratory of Disaster Prevention and Structural Safety of Ministry of Education, Guangxi University, Nanning 530004, China


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