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CONTENTS
Volume 27, Number 2, February 2021
 


Abstract
In this study, the effect of steel fiber utilization, boundary conditions, different beam cross-section, and length parameter are investigated on the free vibration behavior of fiber reinforced self-compacting concrete beam on elastic foundation. In the analysis of the beam model recommended by Euler-Bernoulli, a method utilizing Stokes transformations and Fourier Sine series were used. For this purpose, in addition to the control beam containing no fiber, three SCC beam elements were prepared by utilization of steel fiber as 0.6% by volume. The time-dependent fresh properties and some mechanical properties of self-compacting concrete mixtures were investigated. In the modelled beam, four different beam specimens produced with 0.6% by volume of steel fiber reinforced and pure (containing no fiber) SCC were analyzed depending on different boundary conditions, different beam cross-sections, and lengths. For this aim, the effect of elasticity of the foundation, cross-sectional dimensions, beam length, boundary conditions, and steel fiber on natural frequency and frequency parameters were investigated. As a result, it was observed that there is a noticeable effect of fiber reinforcement on the dynamic behavior of the modelled beam.

Key Words
vibration analysis; Euler-Bernoulli beam; fiber-reinforced SCC; elastic foundation; natural frequency

Address
Mahmut Tunahan Ozdemir, Veysel Kobya: Civil Engineering Department, Institute of Science and Technology, Bursa Uludag University, Gorükle 16240, Turkey
Mustafa Ozgur Yayli, Ali Mardani-Aghabaglou: Civil Engineering Department, Faculty of Engineering, Bursa Uludag University, Gorükle 16240, Turkey

Abstract
Experimental and discrete element methods were used to investigate the effects of echelon non-persistent joint on the failure behaviour of joint's bridge area under uniaxial compressive test. Concrete samples with dimension of 150 mmx100 mmx50 mm were prepared. Uniaxial compressive strength and tensile strength of concrete were 14 MPa and 1MPa, respectivly. Within the specimen, three echelon non-persistent notches were provided. These joints were distributed on the three diagonal plane. the angle of diagonal plane related to horizontal axis were 15o, 30o and 45o. The angle of joints related to diagonal plane were 30o, 45o, 60o. Totally, 9 different configuration systems were prepared for non-persistent joint. In these configurations, the length of joints were taken as 2 cm. Similar to those for joints configuration systems in the experimental tests, 9 models with different echelon non-persistent joint were prepared in numerical model. The axial load was applied to the model by rate of 0.05 mm/min. the results show that the failure process was mostly governed by both of the non-persistent joint angle and diagonal plane angle. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. The strength of samples increase by increasing both of the joint angle and diagonal plane angle. The failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods.

Key Words
echelon non-persistent joint; joint angle; PFC2D

Address
V. Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
S. Abharian: Department of Mining and metallurgical engineering, Amirkabir university, Tehran, Iran
E. Zarrin Ghalam: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran

Abstract
In the present work, an extensive study for predicting efficiency parameters (ji) of various simulated nanocomposites including Polymethyl methacrylate (PMMA) as matrix and different structures including various sizes of graphene platelets (GPLs), single, double, and multi-walled carbon nanotubes (SWCNTs-DWCNTs-MWCNTs), and single and double-walled boron nitride nanotubes (SWBNNTs-DWBNNTs) are investigated. It should be stated that GPLs, carbon and boron nitride nanotubes (CNTs, BNNT) with different chiralities (5, 0), (5, 5), (10, 0), and (10, 10) as reinforcements are considered. In this research, molecular dynamics (MDs) method with Materials studio software is applied to examine the mechanical properties (Young's modulus) of simulated nanocomposite boxes and calculate i of each nanocomposite boxes. Then, it is noteworthy that by changing length (6.252, 10.584, and 21.173 nm) and width (7.137, 10.515, and 19.936) of GPLs, j1, j2, and j3 approximately becomes (0.101, 0.114, and 0.124), (1.15, 1.22, and 1.26), (1.04, 1.05, and 1.07) respectively. After that efficiency parameters of SWCNTs, DWCNTs, and MWCNTs are calculated and discussed separately. Finally efficiency parameters of SWBNNTs and DWBNNTs with different chiralities by PMMA as matrix are determined by MD and discussed separately. It is known that the accurate efficiency parameters helps a lot to calculate the properties of nanocomposite analytically. In particular, the obtained results from this research can be used for analytical work based on the extended rule of mixture (ERM) in bending, buckling and vibration analysis of structure in future study.

Key Words
multiscale modeling; efficiency parameter; molecular dynamics; polymethyl methacrylate as matrix; GPL/CNT/BNNT as reinforcement; different chiralities

Address
Ashkan Farazin and Mehdi Mohammadimehr: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran

Abstract
This paper aims at investigating the capability of different FRP/concrete interface models to predict the effect of carbon nanotubes on the flexural behavior of RC beams strengthened with CFRP. Three different interfacial bond models are proposed to simulate the adhesion between CFRP composites and concrete, namely: full bond, nonlinear spring element, and cohesive zone model. 3D Nonlinear finite element model is developed then validated using experimental work conducted by the authors in a previous investigation. Cohesive zone model (CZM) has the best agreement with the experimental results in terms of load-deflection response. CZM is the only bond model that accurately predicted the cracks patterns and failure mode of the strengthened RC beams. The FE model is then expanded to predict the effect of bond strength on the flexural capacity of RC beams strengthened with externally bonded CNTs modified CFRP composites using CZM bond model. The results reveal that the flexural capacity of the strengthened beams increases with increasing the bond strength value. However, only 23% and 22% of the CFRP stress and strain capacity; in the case of full bond; can be utilized before failure.

Key Words
finite element; bond model; RC beams; strengthening; CFRP; CNTs

Address
Mohammad R. Irshidat and Rami S. Alhusban: Department of Civil Engineering, Jordan University of Science and Technology, Irbid, Jordan

Abstract
Large dams are a part of the infrastructure of any society, and a huge amount of resources are consumed to build them. Among the various types of dams, the optimum design of concrete gravity dams requires special attention because these types of dams require a huge amount of concrete for their construction. On the other hand, concrete gravity dams are among the structures whose design, regarding the acting forces, geometric parameters, and resistance and stability criteria, has some complexities. In the present study, an optimization methodology is proposed based on Sequential Quadratic Programming (SQP), and a computer program is developed to perform optimization of concrete gravity dams. The optimum results for 45 concrete gravity dams are studied and regression analyses are performed to obtain some explicit formulas for optimization of the gravity dams. The optimization of concrete gravity dams can be provided easily using the developed formulas, without the need to perform any more optimization process.

Key Words
dams; concrete gravity dams; optimization; SQP; regression analysis

Address
Alireza Habibi: Department of Civil Engineering, Shahed University, Tehran, Iran
Sajad Zarei: Department of Civil Engineering, University of Kurdistan, Sanandaj, Iran; Technical Department, Kaboudarahang Municipality, Kaboudarahang, Iran
Nima Khaledy: Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran

Abstract
This paper aims to simulate the isotropic elastic damage theory of Liu Jun (2012) using the self-programmed UMAT subroutine in the interface of ABAQUS. Liu Jun (2012)'s method based on the mechanic theory can not be used interactively with the currently commonly used finite element software ABAQUS. The advantage of this method in the paper is that it can interact with ABAQUS and provide a constitutive program framework that can be modified according to user need. The model retains the two scalar damage variables and the corresponding two energy dissipation mechanisms and damage criteria for considering the tensile and compressive asymmetry of concrete. Taking C45 concrete as an example, the relevant damage evolution parameters of its tensile and compressive constitutive model are given. The study demonstrates that the uniaxial tensile stress calculated by the subroutine is almost the same as the Chinese Concrete Design Specification (GB50010) before the peak stress, but ends soon after the peak stress. The stress-strain curve of uniaxial compression calculated by the subroutine is in good agreement with the peak stress in Chinese Concrete Design Specification (GB50010), but there is a certain deviation in the descending stage. In addition, this paper uses the newly compiled subroutine to simulate the shear bearing capacity of the shear key in a new structural system, namely the open-web sandwich slab. The results show that the damage constitutive subroutine has certain reliability.

Key Words
UMAT; subroutine; elastic damage; verification; shear key

Address
Pan Pan Liu: School of Civil and Environmental Engineering, Harbin Institute of Technology, Shenzhen, China
Bo Shen: Space Structures Research of Center, Guizhou University, China

Abstract
In this paper, the parameters of haunch height, reinforcement ratio and site condition were evaluated for the influence on the seismic performance of a composite precast fabricated utility tunnel by shaking table test and numerical simulation. The dynamic response laws of acceleration, interlayer displacement and steel strain under unidirectional horizontal seismic excitation were analyzed through four specimens with a similarity ratio of 1:6 in the test. And a numerical model was established and analyzed by the finite element software ABAQUS based on the structure of utility tunnel. The results indicated that composite precast fabricated utility tunnel with the good anti-seismic performance. In a certain range, increasing the height of haunch or the ratio of reinforcement could reduce the influence of seismic wave on the utility tunnel structure, which was beneficial to the structure earthquake resistance. The clay field containing the interlayer of liquefied sandy soil has a certain damping effect on the structure of the utility tunnel, and the displacement response could be reduced by 14.1%. Under the excitation of strong earthquake, the reinforcement strain at the side wall upper end and haunches of the utility tunnel was the biggest, which is the key part of the structure. The experimental results were in good agreement with the fitting results, and the results could provide a reference value for the anti-seismic design and application of composite precast fabricated utility tunnel.

Key Words
composite precast fabricated utility tunnel; anti-seismic performance; haunch height; site condition; reinforcement ratio

Address
Yanmin Yang, Zigen Li, Ran Xu, Yunke Wang: School of Civil Engineering, Jilin Jianzhu University, Changchun 130118, China
Yongqing Li: Institute of Water Conservancy and Planning Research, Changchun City, Changchun 130000, China

Abstract
The incorporation of pozzolans to Portland cement pastes adds value in the development of new materials for the construction industry. This study presents a new computational method, complementary to the pozzolanic identification by compressive strength at 28 days method, for supporting the validation of pozzolanic mortars for non-structural purposes. An algorithm capable of classifying the pixels of micrographs of specimens fragments was developed. Therefore, comparative analyses were generated from fractional Gaussian representations in four intervals of the same amplitude that indicated the predispositions to form larger void indices (intervals 1 and 2). The results showed that the computational method indicators are in accordance with the physical and chemical indicators.

Key Words
pozzolan; mortars microstructure; micrographs computational analysis; algorithm of image analysis; new pozzolanic method

Address
Rafael G.D. Molin Filho: Department of Chemical Engineering, State University of Maringa, Av. Colombo, 5,790, D - 90, CEP 87020-900, Brazil; Advanced Campus in Jandaia do Sul, Federal University of Parana, Rua Joao Maximiano, 426, Vila Operaria, CEP 86900-000, Brazil
Jaciele M. Rosso: Department of Physics, State University of Maringa, Av. Colombo, 5790, G - 56, CEP 87020-900, Brazil
Eduardo A. Volnistem: Department of Physics, State University of Maringa, Av. Colombo, 5790, G - 56, CEP 87020-900, Brazil
Romel D. Vanderlei: Department of Civil Engineering, State University of Maringa, Av. Colombo, 5790, C - 67, CEP 87020-900, Brazil
Daniel A. Longhi: Advanced Campus in Jandaia do Sul, Federal University of Parana, Rua João Maximiano, 426, Vila Operaria, CEP 86900-000, Brazil
Rodrigo C.T. de Souza: Advanced Campus in Jandaia do Sul, Federal University of Parana, Rua João Maximiano, 426, Vila Operaria, CEP 86900-000, Brazil
Paulo R. Paraíso: Department of Chemical Engineering, State University of Maringa, Av. Colombo, 5,790, D - 90, CEP 87020-900, Brazil
Luiz M. de M. Jorge: Department of Chemical Engineering, State University of Maringa, Av. Colombo, 5,790, D - 90, CEP 87020-900, Brazil


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