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CONTENTS
Volume 26, Number 2, August 2020
 

Abstract
In this study, a two dimensional model of receding contact problem has been analyzed using finite element method (FEM) based software ANSYS and ABAQUS. For this aim finite element modeling of elastic layer and two homogeneous, isotropic and symmetrical elastic quarter planes pressed by means of a rigid circular punch has been presented. Mass forces and friction are neglected in the solution. Since the problem is examined for the plane state, the thickness along the z-axis direction is taken as a unit. In order to check the accuracy of the present models, the obtained results are compared with the available results of the open literature as well as the results of two software are compared using Root Mean Square Error (RMSE) and good agreements are found. Numerical analyses are performed considering different values of the external load, rigid circular radius, quarter planes span length and material properties. The contact lengths and contact stresses of these values are examined, and their results are presented. Consequently, it is concluded that the considered non-dimensional quantities have noteworthy influence on the contact lengths and contact stress distributions, additionally if FEM analysis is used correctly, it can be an efficient alternative method to the analytical solutions that need time.

Key Words
contact mechanics; contact areas; contact stress; FEM

Address
Murat Yaylaci: Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey
Mehmet Avcar: Department of Civil Engineering, Suleyman Demirel University, 32260, Isparta, Turkey

Abstract
To reduce the damage of concrete in fire, a new type of lightweight cinder aggregate concrete was developed due to the excellent fire resistance of cinder. To further enhance its fire resistance, Polypropylene (PP) Fibers which can enhance the fire resistance of concrete were also used in this type of concrete. However, the bond behavior of this new type of concrete after fire exposure is still unknown. To investigate its bond behavior, 185 specimens were heated up to 22, 200, 400, 600 or 800oC for 2 h duration respectively, which is followed by subsequent compressive and tensile tests at room temperature. The concreterebar bond strength of C30 PP fiber-reinforced cinder concrete was subsequently investigated through pull-out tests after fire exposure. The microstructures of the PP fiber-reinforced cinder concrete and the status of the PP fibre at different temperature were inspected using an advanced scanning electron microscopy, aiming to understand the mechanism of the bonding deterioration under high temperature. The effects of rebar diameter and bond length on the bond strength of PP fiber-reinforced cinder concrete were investigated based on the test results. The bond-slip relation of PP fiber-reinforced cinder concrete after exposure at different temperature was derived based on the test results.

Key Words
cinder; bond strength; fire performance PP fibre; fire test

Address
Bin Cai: School of Civil Engineering, Jilin Jianzhu University, Changchun, 130118, China; School of Mathematics, Computer Science and Engineering, City, University of London, London, EC1V 0HB, UK
Ansheng Wu: School of Civil Engineering, Jilin Jianzhu University, Changchun, 130118, China
Feng Fu: School of Mathematics, Computer Science and Engineering, City, University of London, London, EC1V 0HB, UK

Abstract
There is an inherent randomness for concrete microstructure even with the same manufacturing process. Meanwhile, the concrete material under the aqueous environment is usually not fully saturated by water. This study aimed to develop a stochastic micromechanical framework to investigate the probabilistic behavior of the unsaturated concrete from microscale level. The material is represented as a multiphase composite composed of the water, the pores and the intrinsic concrete (made up by the mortar, the coarse aggregates and their interfaces). The differential scheme based two-level micromechanical homogenization scheme is presented to quantitatively predict the concrete\'s effective properties. By modeling the volume fractions and properties of the constituents as stochastic, we extend the deterministic framework to stochastic to incorporate the material\'s inherent randomness. Monte Carlo simulations are adopted to reach the different order moments of the effective properties. A distribution-free method is employed to get the unbiased probability density function based on the maximum entropy principle. Numerical examples including limited experimental validations, comparisons with existing micromechanical models, commonly used probability density functions and the direct Monte Carlo simulations indicate that the proposed models provide an accurate and computationally efficient framework in characterizing the material\'s effective properties. Finally, the effects of the saturation degrees and the pore shapes on the concrete macroscopic probabilistic behaviors are investigated based on our proposed stochastic micromechanical framework.

Key Words
unsaturated concrete; probabilistic behaviors; effective properties; deterministic and stochastic micromechanics; distribution-free method; differential scheme; Monte Carlo simulations

Address
Qing Chen: Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering, University of Mining & Technology, Jiangsu, 221116, China; Key Laboratory of Advanced Civil Engineering Materials, Tongji University, Ministry of Education, 4800 Cao\'an Road, Shanghai 201804, China; School of Materials Science and Engineering, Tongji University, Shanghai 201804, China
Zhiyuan Zhu: School of Materials Science and Engineering, Tongji University, Shanghai 201804, China
Fang Liu: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China
Haoxin Li: Key Laboratory of Advanced Civil Engineering Materials, Tongji University, Ministry of Education,
4800 Cao\'an Road, Shanghai 201804, China; School of Materials Science and Engineering, Tongji University, Shanghai 201804, China
Zhengwu Jiang: Key Laboratory of Advanced Civil Engineering Materials, Tongji University, Ministry of Education,
4800 Cao\'an Road, Shanghai 201804, China; School of Materials Science and Engineering, Tongji University, Shanghai 201804, China

Abstract
In this paper, the bending behavior of single-walled carbon nanotube-reinforced composite (CNTRC) laminated plates is studied using various shear deformation plate theories. Several types of reinforcement material distributions, a uniform distribution (UD) and three functionally graded distributions (FG), are inspected. A generalized higher-order deformation plate theory is utilized to derive the field equations of the CNTRC laminated plates where an analytical technique based on Navier\'s series is utilized to solve the static problem for simply-supported boundary conditions. A detailed numerical analysis is carried out to examine the influence of carbon nanotube volume fraction, laminated composite structure, side-to-thickness, and aspect ratios on stresses and deflection of the CNTRC laminated plates.

Key Words
bending; carbon nanotube-reinforced composites; laminated plates; generalized higher-order deformation plate theory; simply-supported edge conditions

Address
Ahmed Amine Daikh: Structural Engineering and Mechanics of Materials Laboratory, Department of Civil Engineering, Mascara, Algeria; Mechanics of Structures and Solids Laboratory, Faculty of Technology, University of Sidi Bel Abbes, Algeria
Ismail Bensaid: IS2M Laboratory, Faculty of Technology, Mechanical Engineering Department, Tlemcen University, Algeria
Attia Bachiri: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
Mohamed Sid Ahmed Houari: Mechanics of Structures and Solids Laboratory, Faculty of Technology, University of Sidi Bel Abbes, Algeria
Abdelouahed Tounsi: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum and Minerals, 31261, Dhahran, Eastern Province, Saudi Arabia
Tarek Merzouki: LISV, University of Versailles Saint-Quentin, 10-12 Avenue de l\'Europe, 78140, Vélizy, France

Abstract
This paper presents an evaluation of shear transfer across cracks in reinforced concrete through finite element modelling (FEM) and analytical predictions. The aggregate interlock is one of the mechanisms responsible for the shear transfer between two slip surfaces of a crack; the others are the dowel action, when the reinforcement contributes resisting a parcel of shear displacement (reinforcement), and the uncracked concrete comprised by the shear resistance until the development of the first crack. The aim of this study deals with the development of a 3D numerical model, which describes the behavior of Z-type push-off specimen, in order to determine the properties of interface subjected to direct shear in terms cohesion and friction angle. The numerical model was validated based on experimental data and a parametric study was performed with the variation of the concrete strength. The numerical results were compared with analytical predictions and a new equation was proposed to predict the maximum shear stress in cracked concrete.

Key Words
shear strength; finite element modeling; aggregate interlock; push-off test; Z-type specimen, numerical analysis

Address
Marcela N. Kataoka, Ana Lucia H.C. El Debs: Structural Department, Engineering School of Sao Carlos, University of Sao Paulo, Av. Trabalhador, Saocarlense, no 400, CEP: 13566-580 Sao Carlos, SP, Brazil
Daniel de L. Araujo, Barbara G. Martins: School of Civil and Environmental Engineering, Federal University of Goias,
Universitaria Street, no 1488, Qd 86, Setor Universitario, Goiania, GO 74605-220, Brazil

Abstract
Shear keys in precast concrete segmental bridges (PCSBs) are usually match-casting which is very labour intensive. In this research, an innovative match-casting-free construction was proposed by leaving small gap between the convex and the concave castellated shear keys in the joints of PCSBs. Specimen experiment, shear strength analysis and numerical simulation were conducted, investigating the loading performance of this new type of dry joints, the gap dry joints. Compared with matchcasting joint specimens, it has been found from experiment that shear capacity of gap joint specimens significantly decreased ranging from 17.75% to 42.43% due to only partially constrained and contacted in case of gap dry joints. Through numerical simulation, the effects of bottom contacting location, the heights of the gap and the shear key base were analyzed to investigate strength reduction and methods to enhance shear capacity of gap joint specimens. Numerical results proved that shear capacity of gap dry joints under full contact condition was higher than that under partial contact. In addition, left contact destroyed the integrity of shear keys, resulting in significant strength reduction. Larger shear key base remarkably increased shear capacity of the gap joint. Experimental tests indicated that AASHTO provision underestimated shear capacity of the match-casting dry joint specimens, while the numerical results for the gap dry joint showed that AASHTO provision underestimated shear capacity of full contact specimens, but overestimated that of left contact specimens.

Key Words
direct shear; matching joint; gap joint; strength reduction; code evaluation; numerical simulation

Address
Haibo Jiang, Jiahui Feng, Jie Xiao, Mingzhu Chen and Weibin Liang: School of Civil and Transportation Engineering, Guangdong University of Technology, Guangzhou Higher Education Mega Center, Guangzhou 510006, China

Abstract
Fly ash has become an important component of concrete as supplementary cementitious material with the development of concrete technology. To make use of fly ash efficiently, four types of fly ash with particle size distributions that are in conformity with four functions, namely, S.Tsivilis, Andersen, Normal and F distribution, respectively, were prepared. The four particle size distributions as functions of the strength and pore structure of concrete were thereafter constructed and investigated. The results showed that the compressive and flexural strength of concrete with the fly ash that conforming to S.Tsivilis, Normal, F distribution increased by 5-10 MPa and 1-2 MPa, respectively, compared to the reference sample at 28 d. The pore structure of the concrete was improved, in which the total porosity of concrete decreased by 2-5% at 28 d. With regarding to the fly ash with Andersen distribution, it was however not conducive to the strength development of concrete. Regression model based on the grey multiple linear regression theory was proved to be efficient to predict the strength of concrete, according to the characteristic parameters of particle size and pore structure of the fly ash.

Key Words
fly ash; particle size; concrete; grey multiple linear regression

Address
Yunpeng Cui: Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian, China
Jun Liu: School of Materials Science and Engineering, Shenyang Ligong University, Shenyang, China
Licheng Wang: Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian, China
Runqing Liu: School of Materials Science and Engineering, Shenyang Ligong University, Shenyang, China
Bo Pang: Faculty of Infrastructure Engineering, Dalian University of Technology, Dalian, China

Abstract
This research is devoted to investigate the bending and free vibration behaviour of laminated composite/sandwich plates and shells, by applying an analytical model based on a generalized and simple refined higher-order shear deformation theory (RHSDT) with four independent unknown variables. The kinematics of the proposed theoretical model is defined by an undetermined integral component and uses the hyperbolic shape function to include the effects of the transverse shear stresses through the plate/shell thickness; hence a shear correction factor is not required. The governing differential equations and associated boundary conditions are derived by employing the principle of virtual work and solved via Navier-type analytical procedure. To verify the validity and applicability of the present refined theory, some numerical results related to displacements, stresses and fundamental frequencies of simply supported laminated composite/sandwich plates and shells are presented and compared with those obtained by other shear deformation models considered in this paper. From the analysis, it can be concluded that the kinematics based on the undetermined integral component is very efficient, and its use leads to reach higher accuracy than conventional models in the study of laminated plates and shells.

Key Words
bending; free vibration; laminated composite; sandwich; shell

Address
Othmane Allam: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Kada Draiche: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria; Departement de Genie Civil, Universite Ibn Khaldoun Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algerie
Abdelmoumen Anis Bousahla: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
Fouad Bourada: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria; Departement des Sciences et de la Technologie, Centre Universitaire de Tissemsilt, BP 38004 Ben Hamouda, Algeria
Abdeldjebbar Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
Kouider Halim Benrahou: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
S.R. Mahmoud: GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia
E.A. Adda Bedia: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia
Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia


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