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CONTENTS
Volume 23, Number 4, April 2019
 

Abstract
The discontinuous Galerkin method (DGM) has become widely used as it possesses several qualities, such as a natural ability to dealing with discontinuities. DGM has its major success related to fluid mechanics. Its major importance is the ability to deal with discontinuities and still provide high order of approximation. That is an important advantage when simulating cracking propagation. No remeshing is necessary during the propagation, since the crack path follows the interface of elements. However, DGM comes with the drawback of an increased number of degrees of freedom when compared to the classical continuous finite element method. Thus, it seems a natural approach to combine them in the same simulation obtaining the advantages of both methods. This paper proposes the application of the combined continuous-discontinuous Galerkin method (CDGM) to crack propagation. An important engineering problem is the simulation of crack propagation in concrete structures. The problem is characterized by discontinuities that evolve throughout the domain. Crack propagation is simulated using CDGM. Discontinuous elements are placed in regions with discontinuities and continuous elements elsewhere. The cohesive zone model describes the fracture process zone where softening effects are expressed by cohesive zones in the interface of elements. Two numerical examples demonstrate the capacities of CDGM. In the first example, a plain concrete beam is submitted to a three-point bending test. Numerical results are compared to experimental data from the literature. The second example deals with a full-scale ground slab, comparing the CDGM results to numerical and experimental data from the literature.

Key Words
finite elements; discontinuous Galerkin; cracking propagation; cohesive fracture; concrete; steel-fiber reinforced concrete

Address
Tiago L.D. Forti: Simworx R&D, Campinas-SP, Brazil
Nadia C.S. Forti: Pontifical Catholic University of Campinas, Campinas-SP, Brazil
Fábio L.G. Santos: Simworx R&D, Campinas-SP, Brazil
Marco A. Carnio: Evolução Engenharia, Valinhos-SP, Brazil

Abstract
The studies on the applications of waste materials in concrete have been increased in Iraq since 2003. In this research, rubber wastes that resulting from scrapped tires was added to concrete mix with presence of superplasticizer. The mechanical properties of concrete and workability of concrete mixes were studied. The used rubber were ranging in size from (2-4) mm with addition percentages of (0.1% and 0.2%) by volume of concrete. The results of mechanical properties of concrete show that rubber enhance the ductility, and compressive and tensile strength compared to concrete without it. Also, the flexural behavior of hybrid strength concrete beams (due to using rubber at the bottom or top layer of section) was investigated. The rubber concrete located at bottom layer gives higher values of ultimate loads and deflections compared to the beam with top layer. A similar response to fiber concrete beam (all section contains 0.1% rubber) was recognized. Finite element modeling in three dimensions was carried for the tested beams using ABAQUS software. The ultimate loads and deflection obtained from experimental and finite elements are in good agreements with average difference of 8% in ultimate load and 20% in ultimate deflection.

Key Words
reinforced concrete; waste rubber; experimental test; finite element analysis; hybrid section

Address
Adel A. Al-Azzawi, Noora Saad and Dalia Shakir: Civil Engineering Department, College of Engineering, Al-Nahrain University, Baghdad, Iraq

Abstract
The potential of using genetic programming to predict engineering data has caught the attention of researchers in recent years. The present paper utilized weighted genetic programming (WGP), a derivative model of genetic programming (GP), to model the compressive strength of concrete. The calculation results of Abrams\' laws, which are used as the design codes for calculating the compressive strength of concrete, were treated as the inputs for the genetic programming model. Therefore, knowledge of the Abrams\' laws, which is not a factor of influence on common data-based learning approaches, was considered to be a potential factor affecting genetic programming models. Significant outcomes of this work include: 1) the employed design codes positively affected the prediction accuracy of modeling the compressive strength of concrete; 2) a new equation was suggested to replace the design code for predicting concrete strength; and 3) common data-based learning approaches were evolved into knowledge-based learning approaches using historical data and design codes.

Key Words
genetic programming; concrete compressive strength; design codes; functional mapping

Address
Hsing-Chih Tsai and Min-Chih Liao: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, #43, Sec. 4, Keelung Rd., Taipei, Taiwan, R.O.C.

Abstract
In order to study the effect of moisture on the compressive strength of low-strength hollow concrete blocks, an experimental study was carried out on 96 samples of locally manufactured hollow concrete blocks collected from three different locations. Uniaxial compression tests were conducted on dry specimens and three types of saturated specimens with moisture contents of 30%, 50% and 80% respectively. The range of moisture content adopted covered the range within which the concrete block samples are saturated in the dry and monsoon seasons. The compressive strength of low-strength hollow concrete blocks decreases with increase in moisture content and the relationship between compressive strength of hollow concrete blocks and their moisture content can be considered to be linear. However, the strength degradation of 30% moist concrete blocks with respect to dry blocks is relatively low and can be considered to be comparable to dry concrete blocks. A formula indicating the relationship between the moisture content and compressive strength of low-strength hollow concrete blocks is also proposed.

Key Words
hollow concrete blocks; masonry; low-strength; moisture

Address
Hopeful Syiemiong and Comingstarful Marthong: Department of Civil Engineering, National Institute of Technology Meghalaya, Shillong, India

Abstract
Corrosion of the rebar embedded in concrete has a fundamental role in the determination of life and durability of the concrete structures. Researches have demonstrated that artificial neural networks (ANNs) can effectively predict issues such as expected damage in concrete structures in marine environment caused by chloride penetration, the potential of steel embedded in concrete under the influence of chloride, the corrosion of the steel embedded in concrete and corrosion current density in steel reinforced concrete. In this study, data from different kind of concrete under the influence of chloride ion, are analyzed using the neural network and it is concluded that this method is able to predict the bond strength between the concrete and the steel reinforcement in mentioned condition with high reliability.

Key Words
corrosion of steel; concrete; artificial neural networks; modelling; bond strength

Address
Amir Shirkhani, Daniel Davarnia and Bahman Farahmand Azar: Department of Structural Engineering, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

Abstract
The post-fire behavior of structural elements and the cooling process has always been one of the main concerns of the structural engineers. The structures can be cooled at different rates, where they affect the structure‟s behavior. In the present study, a numerical model has been developed using the Abaqus program to investigate the effect of cooling rate on the post-fire behavior of the CFST column. To verify the model, results of an experimental study performed on CFST columns within a full heating and cooling cycle have been used. In this model, coMParison of the residual strength has been employed in order to examine the behavior of CFST column under different cooling rates. Furthermore, a parametric study was carried out on the strength of steel and concrete, the height of the specimens, the axial load ratio and the cross-sectional shape of the specimen through the proposed model. It was observed that the cooling rate affects the behavior of the column after the fire, and thus the higher the specimen\'s temperature is, the more effect it has on the behavior. It was also noticed that water cooling had slightly more residual strength than natural cooling. Furthermore, it was recognized from the parametric study, that by increasing the strength of steel and concrete and the load ratio, as well as modifying the cross-sectional shape from circular to square, residual strength of column at the cooling phase was less than that of the heating phase. In addition, with reducing column height, no change was witnessed in the column behavior after the cooling phase.

Key Words
water cooling; Natural cooling; cooling rate; post-fire; residual strength

Address
Alireza Afaghi-Darabi and Gholamreza Abdollahzadeh: Department of Civil Engineering, Babol Noshirvani University of Technology, Shariati Av., Babol, Mazandaran, Iran

Abstract
In this paper, buckling analyses of composite concrete plate reinforced by piezoelectric nanoparticles is studied. The Halphin-Tsai model is used for obtaining the effective material properties of nano composite concrete plate. The nano composite concrete plate is modeled by Third order shear deformation theory (TSDT). The elastic medium is simulated by Winkler model. Employing nonlinear strains-displacements, stress-strain, the energy equations of concrete plate are obtained and using Hamilton\'s principal, the governing equations are derived. The governing equations are solved based on Navier method. The effect of piezoelectric nanoparticles volume percent, geometrical parameters of concrete plate and elastic foundation on the buckling load are investigated. Results showed that with increasing Piezoelectric nanoparticles volume percent, the buckling load increases.

Key Words
buckling; nanocomposite concrete plate; concrete plate; Reddy theory; Halphin-Tsai model

Address
Reza Taherifar: Department of Civil Engineering, Meymeh Branch, Islamic Azad University, Meymeh, Iran
Maryam Mahmoudi: Department of Computer Engineering, Meymeh Branch, Islamic Azad University, Meymeh, Iran
Mohammad Hossein Nasr Esfahani: Department of Mathematics, Faculty of Basic Science, Meymeh Branch, Islamic Azad University, Meymeh, Iran
Neda Ashrafi Khuzani: Department of Computer Engineering, Meymeh Branch, Islamic Azad University, Meymeh, Iran
Shabnam Nasr Esfahani: Department of Electrical Engineering, Meymeh Branch, Islamic Azad University, Meymeh, Iran
Farhad Chinaei: Department of Civil and Mineral Engineering, Meymeh Branch, Islamic Azad University, Meymeh Iran


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