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CONTENTS
Volume 28, Number 2, August 2021
 

Abstract
This paper evaluated the bond behavior between recycled crumb rubber (CR) concrete and fiber reinforced polymer (FRP) bar. An experimental study consisting of fifty-seven pull-out specimens with fine recycled crumb rubber aggregate content of 0%, 5%,10% and 15% was described. The results showed that recycled crumb rubber concrete pull-out specimens exhibited similar bond stress-slip curves, which had four stages: the micro-slip, concrete internal cracking, pullout and residual stages. The use of crumb rubber in concrete reduced the bond strength. The bond strength decreased with the increase of the compressive strength of recycled crumb rubber concrete. The type and content of recycled crumb rubber also affected the bond strength. The glass fiber reinforced polymer (GFRP) bars tended to have stronger bonds than that of basalt fiber reinforced polymer (BFRP) bars.

Key Words
bond strength; concrete; crumb rubber; FRP; pull-out

Address
Jiongfeng Liang: Faculty of Civil & Architecture Engineering, East China University of Technology, Nanchang, P.R. China; Key Laboratory for Structural Engineering and Disaster Prevention of Fujian Province, Huaqiao University, Xiamen, P.R. China
Jianguo Liu: Faculty of Civil & Architecture Engineering, East China University of Technology, Nanchang, P.R. China
Li Fan: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, P.R. China
Rui Ren: School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, P.R. China
Wei Li: College of Civil Engineering and Architecture, Wenzhou University, Wenzhou, P.R. China
Wenrui Yang: Faculty of Civil & Architecture Engineering, East China University of Technology, Nanchang, P.R. China

Abstract
Recycled aggregate concrete (RAC) is considered a good way of sustainable development, but compared with natural coarse aggregates (NCA), the performance of recycled coarse aggregates (RCA) is often worse. This study aimed at the basalt fiber (BF) enhances the frost resistance of RAC. Therefore, a rapid freeze-thaw cycles test was carried out on basalt fiber reinforced recycled aggregate concrete (BFRRC), with the variation of three different replacement ratios of RCA (i.e., 0, 50 and 100%) and four different contents of BF (i.e., 0, 2, 4 and 6 kg/m3). Then, the damage appearance, mass losses, and relative dynamic elastic modulus (RDEM) of specimens were analyzed. Results were showed that the appearance damage characteristics of RAC are different from NAC, as the replacement ratio of RCA was increased, the damage appearance of the specimens was exacerbated, and surface spalling transformed into corner spalling and holes were generated in the surfaces of the specimens. Compared with mass loss, REDM can better reflect the frost resistance of BFRRC. BF could significantly improve the damage appearance and RDEM loss of the specimens, incorporating 4 kg/m3 of BF can significantly improve the frost resistance of RAC. In addition, the mechanism of freeze–thaw damage was revealed by using scanning electron microscopy (SEM) and damage theory, a freeze–thaw damage model of BFRRC was established by defining the damage degree on the basis of the RDEM. The results of this work could provide a reference for the further research and engineering application of BFRRC.

Key Words
basalt fiber; freeze–thaw damage model; freeze–thaw resistance; recycled aggregate concrete; relative dynamic elastic modulus

Address
Yahong Ding, Shuqi Guo: School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, China
Xianggang Zhang: School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, China; Henan Key Laboratory of Special Protective Materials, Luoyang 471023, Henan, China
Meixiang Zhang: School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, China; School of Architectural Engineering, Xinyu University, Xinyu 338000, Jiangxi, China
Jun Wu: School of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, China

Abstract
Properties of wet and set concrete are influenced by a wide range of variables. With new formulations being tried and adopted, understanding workability, strength and durability characteristics of these formulations is of utmost importance. From among the wide range of variables that affect properties of concrete, identification of the most vital, interplay between variables, quantification of influence, for judicious manipulation of mix proportioning, placement, compaction and curing, to get the desired and targeted end results can vastly be improved by employing the state of the art data handling tools. Group method of data handling (GMDH), a set of mathematical algorithms, is of great usage potential in multi-variable data modeling, optimization and pattern recognition. Proper Orthogonal Decomposition (POD) a subset of GMDH, a technique for systematic dimensionality reduction and pattern recognition, is of great importance in studying complex datasets. This paper presents the need for adoption of GMDH techniques in concrete technology with an account of trends in this direction and also provides an illustration of POD's utility as a valid decision-making tool in dimensionality reduction and projection of behavior of concrete subjected to elevated temperature.

Key Words
concrete; data; performance appraisal; POD; variables

Address
A. Manoj and K.S. Babu Narayan: Department of Civil Engineering, National Institute of Technology Karnataka, Surathkal, 575 025, India

Abstract
Concrete spalling is considered as one of the most common weaknesses phenomena in concrete members. In this article, reinforced concrete (RC) column and beam members are subject to a variety of loads under damaged and strengthened conditions using carbon and glass fiber reinforced polymer (FRP) wraps. The main parameters in this study include the number of the FRP layers, the materials of the strengthening FRP layers, and the loading types. The imposed loads include pure bending moment, shear, and pure torsional moment, to enable studying the structural elements's behaviors under such states. The numerical finite element (FE) model was verified using experimental results, and 10 different case numerical FE models were analyzed. The analysis results demonstrated that using an FRP layer increases the shearing and torsional capacities. Adding another FRP layer does not significantly affect the models' behavioral specifications. In both RC beam and column, this strengthening method did not affect the torsional capacity, while managed to prevent sudden capacity loss and enhance ductility.

Key Words
carbon fiber reinforced polymer (CFRP); damaged reinforced concrete; finite element modeling; glass fiber reinforced polymer (GFRP); strengthening; torsional loading

Address
Mehdi Ebadi-Jamkhaneh: Department of Civil Engineering, School of Engineering, Damghan University, Damghan, Iran
Amir Homaioon-Ebrahimi: Department of Civil Engineering, School of Engineering, University of Birmingham, Birmingham, UK
Denise-Penelope N. Kontoni: Department of Civil Engineering, School of Engineering, University of the Peloponnese, GR-26334 Patras, Greece; School of Science and Technology, Hellenic Open University, GR-26335 Patras, Greece

Abstract
Fire hazard is a high impact threat to human life and engineering structures, which may result in significant loss of strength and huge damage to building components. In order to determine the strength and durability of structural elements after the fire and consequently to clarify the serviceability status for planning the necessary maintenance strategies, the structural behaviours of building elements under elevated temperature is to be precisely evaluated. Therefore, this work generates the accurate structural assessment data for fire performance assessment of reinforce concrete columns and frames by performing heat transfer and modal analyses along with numerical methods using special finite element software. Moreover, the results are compared with both analytical and numerical methods in order to validate the software results. On this basis, the results are first compared with Eurocode 2) as well as Wickström and Hertz methods and then the resulted data are further validated numerically using different software. In other words, this study evaluates the performance of structural elements under fire load, while conducting a comprehensive and detailed performance assessment on dynamic characteristics named as natural frequencies, mode shapes and damping ratios. Moreover, the effects of varying cross-sectional dimensions, concrete grades, exposure durations and different exposure scenarios of reinforce concrete elements are precisely evaluated using parametric analyses, and the resulted data set is presented as set of formulas, nomographs and tables. The parametric study points out the influence of elevated temperatures on natural frequency values and mode shapes. Consequently, the rise in temperature resulted in significant decrease in natural frequency values. However, no specific pattern has been observed for the changes in resulted mode shapes. The outputs are generally based on the natural frequency values and the amount of change in these values for various situations. It is hoped that the results will actively contribute to the further development of existing fire regulations in the area of structural health monitoring at elevated temperatures.

Key Words
column; dynamic characteristic; elevated temperature; finite element method; fire; frame; heat transfer; reinforced concrete; structural health monitoring

Address
Yunus Emrahan Akbulut, Ahmet Can Altunisik, Hasan Basri Basaga, Sara Mostofi: Karadeniz Technical University, Department of Civil Engineering, 61080, Trabzon, Turkey
Ayman Mosallam, Louai F. Wafa: Civil and Environmental Engineering, The Henry Samueli School of Engineering, University of California, Irvine, USA

Abstract
The experimentally tested modelled specimens were simulated by a two-dimensional particle flow code to study the behavior of rock mass surrounding a tunnel interacted with a nearby rock joint or discontinuity. The specially prepared specimens are tested in the laboratory and the measured results are provided. Then a numerical modelling of these tests is accomplished by a calibrated two-dimensional particle flow code to study the rock tunnel behavior while interacting with a neighboring joint. The two-dimensional discrete element code was calibrated using Brazilian tensile test. Then the modelled specimens are provided so that various configurations of tunnel cross sections and the neighboring joints were tested under uniaxial compression condition. This study showed that the tensile cracks are the most dominant mode occurred in these modelled samples. The wing cracks initiated from the joint tips when the joints interacted in a position less than that of the tunnel height. These cracks are then propagated and interacted with the tunnel ceiling. When the joint interacting the tunnel head and the interaction angle is negative the tunnel can be in a stable position considering the joints effect on its instability situation. But for positive interaction angles and the case of joint existing near the tunnel head, the wing cracks may initiate and propagate towards the tunnel ceiling. As the distance of joint from the tunnel ceiling is increased its effect on the tunnel instability is decreased because the failure stress is increased. The number of joints and their distance with the tunnel boundary (ceiling) have also a profound effect on the stability condition of the tunnel. The failure stress reached its maximum value for the increase from -30 to -60 degrees or increase from 30 to 60 degrees. The failure stress also decreased as the number of notches and their lengths increased. In all these interaction scenarios, the corresponding numerical and experimental values compared and it is concluded that the failure stresses are very close to each other which verified the accuracy and applicability of the proposed modeling technic.

Key Words
discrete element method; induced wing crack; interacted joint; tunnel; two dimensions

Address
Fei Zhou: School of Civil Engineering and Architecture, Hubei University of Arts and Science, Xiangyang City, Hubei province, China
Vahab Sarfarazi: Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran
Hadi Haeri: State Key Laboratory for Deep GeoMechanics and Underground Engineering, Beijing, 100083, China
Mohammad Hosein Soleymanipargoo: Department of Civil Engineering, Semnan University, Semnan, Iran
Jinwei Fu: School of Civil Engineering and Transportation, North China University of Water Resources and Electric Power, Zhengzhou, 450046, China
Mohammad Fatehi Marji: Department of Mine Exploitation Engineering, Faculty of Mining and metallurgy, Institute of Engineering, Yazd University, Yazd, Iran

Abstract
This study has been performed to investigate the receding contact problem of a homogeneous orthotropic coating that is not bonded to a homogeneous isotropic substrate without any interfacial defects. The isotropic substrate is supported on a Winkler foundation. The problem is solved assuming that the contact between the rigid punch and orthotropic coating, and that between the orthotropic coating and isotropic substrate, are frictionless. Additionally, the effect of the body forces is neglected, and only compressive normal tractions can be transmitted through the interfaces. The contact analysis of the orthotropic coating, which is subjected to a contact load using a rigid cylindrical punch, is performed under plane strain conditions. The governing equations are analytically found using the theory of elasticity and Fourier integral transformation techniques. Subsequently, the governing equations are reduced to a system of two singular equations, wherein the unknowns are the contact stresses and contact widths. To numerically solve the resulting singular integral equations, Gauss-Chebyshev integration formulas are employed. It is analyzed the influence of the following parameters on the contact stresses and contact widths: orthotropicmaterial properties, punch radius, load ratio, Winkler foundation stiffness.

Key Words
contact stress; isotropic substrate; orthotropic coating; receding contact; singular integral equation

Address
Erdal Öner: Department of Civil Engineering, Bayburt University, 69010, Turkey

Abstract
In the recent year, extensive researches have been done on fly ash-based geopolymer concrete for its similar properties like Portland cement as well as its environmental sustainability. However, it is difficult to provide a consistent method for geopolymer mix design because of the complexity and uncertainty of its design parameters, such as the alkaline solution concentration, mole ratio, and liquid to fly ash mass ratio. These mix-design parameters, along with the curing time and temperature ominously affect the most significant properties of the geopolymer concrete, i.e., compressive strength. To overcome these difficulties, the paper aims to provide a simple mix-design tool using artificial intelligence (AI) models. Three well-established and efficient AI techniques namely, genetic programming, relevance vector machine, and Gaussian process regression are used. Based on the performance of the developed models, it is understood that all the models have the capability to deliver higher prediction accuracies in the range of 0.9362 to 0.9905 (based on R2 value). Among the employed models, RVM outperformed the other model with R2=0.9905 and RMSE=0.0218. Theodore, the developed RVM model is very potential to be a new alternative to assist engineers to save time and expenditure on account of the trial-and-error process in finding the correct design mix proportions.

Key Words
fly ash concrete; Gaussian process regression; genetic programming; relevance vector machine

Address
Rahul Biswas: Department of Civil Engineering, National Institute of Technology Sikkim, India
Abidhan Bardhan, Pijush Samui, Baboo Rai: Department of Civil Engineering Department, National Institute of Technology Patna, India
Subrata Nayak: Structural Engineering, ZURU, Tech, India
Danial Jahed Armaghani: Department of Urban Planning, Engineering Networks and Systems, Institute of Architecture and Construction, South Ural State University, 76, Lenin Prospect, Chelyabinsk 454080, Russia

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