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CONTENTS
Volume 27, Number 3, March 2021
 

Abstract
Throughout the previous years, many efforts focused on incorporating non-biodegradable wastes as a partial replacement and sustainable alternative for natural aggregates in cement-based materials. Currently, rubberized concrete is considered one of the most important green concrete materials produced by replacing natural aggregates with rubber particles from old tires in a concrete mixture. The main benefits of this material, in addition to its importance in sustainability and waste management, comes from the ability of rubber to considerably damp vibrations, which, when used in reinforced concrete structures, can significantly enhance its energy dissipation and vibration behavior. Nowadays, the literature has many experimental findings that provide an interesting view of rubberized concrete's dynamic behavior. On the other hand, it still lacks research that collects, interprets, and numerically investigates these findings to provide some correlations and construct reliable prediction models for rubberized concrete's dynamic properties. Therefore, this study is intended to propose prediction approaches for the dynamic properties of rubberized concrete. As a part of the study, multiple linear regression and artificial neural networks will be used to create prediction models for dynamic modulus of elasticity, damping ratio, and natural frequency.

Key Words
rubberized concrete; structural material; dynamic modulus of elasticity; damping ratio; natural frequency; regression analysis; artificial neural network

Address
Ahed Habib and Umut Yildirim: Department of Civil Engineering, Eastern Mediterranean University, Famagusta, North Cyprus, via Mersin 10, Turkey

Abstract
The aim of this paper was to examine the continuous and discontinuous contact problems between the functionally graded (FG) layer pressed with a uniformly distributed load and homogeneous half plane using an analytical method and FEM. The FG layer is made of non-homogeneous material with an isotropic stress–strain law with exponentially varying properties. It is assumed that the contact at the FG layer-half plane interface is frictionless, and only the normal tractions can be transmitted along the contacted regions. The body force of the FG layer is considered in the study. The FG layer was positioned on the homogeneous half plane without any bonds. Thus, if the external load was smaller than a certain critical value, the contact between the FG layer and half plane would be continuous. However, when the external load exceeded the critical value, there was a separation between the FG layer and half plane on the finite region, as discontinuous contact. Therefore, there have been some steps taken in this study. Firstly, an analytical solution for continuous and discontinuous contact cases of the problem has been realized using the theory of elasticity and Fourier integral transform techniques. Then, the problem modeled and twodimensional analysis was carried out by using ANSYS package program based on FEM. Numerical results for initial separation distance and contact stress distributions between the FG layer and homogeneous half plane for continuous contact case; the start and end points of separation and contact stress distributions between the FG layer and homogeneous half plane for discontinuous contact case were provided for various dimensionless quantities including material inhomogeneity, distributed load width, the shear module ratio and load factor for both methods. The results obtained using FEM were compared with the results found using analytical formulation. It was found that the results obtained from analytical formulation were in perfect agreement with the FEM study.

Key Words
contact mechanics; functionally graded layer; finite element method; contact area; contact stress

Address
Murat Yaylaci: Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey
Gokhan Adiyaman: Department of Civil Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey
Erdal Oner: Department of Civil Engineering, Bayburt University, 69010, Bayburt, Turkey
Ahmet Birinci: Department of Civil Engineering, Recep Tayyip Erdogan University, 53100, Rize, Turkey

Abstract
This paper presents a review of the two widespread approaches which deal with the ultimate strength design of RC slabs subjected to bending moments and torsion: The Field of Moments Method (FoMM) and the Sandwich method (SM). Special attention is paid to the ultimate strain distribution implicitly assumed when using each one of the methodologies, in particular, the yielding of the steel reinforcement. This work analyzes the initial assumption regarding ultimate strain distribution in the SM. Furthermore, this work studies the resisting moments field on which the Wood-Armer method is based, and it finds some inconsistencies. Several examples have been developed.

Key Words
reinforced concrete slab; strain compatibility; ultimate strength design; resisting moments

Address
Luisa Maria Gil-Martin and Enrique Hernandez-Montes: Department of Structural Mechanics, University of Granada, Campus Universitario de Fuentenueva, 18072 Granada, Spain

Abstract
Carbon fiber reinforced polymer (CFRP) has extensive use in strengthening reinforced concrete structures due to its high strength and elastic modulus, low weight, fast and easy application, and excellent durability performance. Many studies have been carried out to determine the performance of the CFRP confined concrete cylinder. Although studies about the prediction of confined compressive strength using ANN are in the literature, the insufficiency of the studies to predict the strain of confined concrete cylinder using ANN, which is the most appropriate analysis method for nonlinear and complex problems, draws attention. Therefore, to predict both strengths and also strain values, two different ANNs were created using an extensive experimental database. The strength and strain networks were evaluated with the statistical parameters of correlation coefficients (R2), root mean square error (RMSE), and mean absolute error (MAE). The estimated values were found to be close to the experimental results. Mathematical equations to predict the strength and strain values were derived using networks prepared for convenience in engineering applications. The sensitivity analysis of mathematical models was performed by considering the inputs with the highest importance factors. Considering the limit values obtained from the sensitivity analysis of the parameters, the performances of the proposed models were evaluated by using the test data determined from the experimental database. Model performances were evaluated comparatively with other analytical models most commonly used in the literature, and it was found that the closest results to experimental data were obtained from the proposed strength and strain models.

Key Words
artificial neural networks; CFRP; confinement; strain model; strength model

Address
Onur Ozturk: Department of Civil Engineering, Kocaeli University, 41380 Kocaeli, Turkey

Abstract
An experimental program was conducted to investigate the fresh properties, mechanical properties and durability characteristics of the self-compacting mortars (SCM) produced with pumice powder and Artificial Lightweight Fine Aggregate (aLWFA). aLWFA was produced by using fly ash. A total of 16 different mixtures were designed with a constant water-binder ratio of 0.37, in which natural sands were partially replaced with aLWFA and pumice powder at different volume fractions of 5%, 10% and 15%. The artificial lightweight aggregates used in this study were manufactured through cold bonding pelletisation of 90% of class-F fly ash and 10% of Portland cement in a tilted pan with an ambient temperature and moisture content. Flowability tests were conducted on the fresh mortar mixtures beforehand, to determine the self-compacting characteristics on the basis of EFNARC. To determine the conformity of the fresh mortar characteristics with the standards, mini-slump and mini-V-funnel tests were carried out. Hardened state tests were conducted after 7, 28 and 56 days to determine the flexural strength and axial compressive strength respectively. Durability, sorptivity, permeability and density tests were conducted at the end of 28 days of curing time. The test results showed that the pumice powder replacement improved both the fresh state and the hardened state characteristics of the mortar and the optimum mixture ratio was determined as 15%, considering other studies in the literature. In the aLWFA mixtures used, the mechanical and durability characteristics of the modified compositions were very close to the control mixture. It is concluded in this study that mixtures with pumice powder replacement eliminated the negative effects of the aLWFA in the mortars and made a positive contribution.

Key Words
self-compacting mortar; pumice powder; durability; lightweight fine aggregate; hardened state tests

Address
Serkan Etli, Selim Cemalgil: Department of Civil Engineering, Munzur University, Aktuluk Campus, 62000, Tunceli, Turkey
Onur Onat: Department of Civil Engineering, Inonu University, 44280, Malatya, Turkey

Abstract
The present paper treats the free vibration problem of the masonry wall strengthened with thin composite plate by viscoelastic adhesive layer. For this goal two steps are considered in the analytical solution. In the first one, an efficient homogenisation procedure is given to provide the anisotropic properties of the masonry wall. The second one is dedicated to purpose simplified mathematical models related to both in-plane and out-of-plane vibration problems. In these models, the higher order shear theories (HSDT's) are employed for a more rigours description of the shear deformation trough the masonry wall and the composite sheet. Ritz's method is deployed as solution strategy in order to get the natural frequencies and their corresponding loss factors. The obtained results are validated with the finite element method (FEM) and then, a parametric study is undertaken for different kinds of masonry walls strengthened with composite sheets.

Key Words
strengthened masonry structures; masonry homogenisation; damping effect; free vibration; viscoelastic materials; composite materials; height shear beam and plate theories; Ritz's method

Address
Salaheddine Laib, Sid Ahmed Meftah: Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, Universite Djillali Liabes, Sidi Bel Abbes, Algerie
Hadj Youzera: Laboratoire d'Etude des Structures et de Mecanique des Materiaux, Departement de Genie Civil, Faculte des Sciences et de la Technologie, Universite Mustapha Stambouli B.P. 305, R.P. 29000 Mascara, Algerie
Noureddine Ziane: Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, Universite Djillali Liabes, Sidi Bel Abbes, Algerie
Abdelouahed Tounsi: YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea; Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261Dhahran, Eastern Province, Saudi Arabia; Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria

Abstract
A dynamic analytical solution for a simply supported, rectangular functionally graded plate with a porous middle layer under time-dependent load based on a refined third-order shear deformation theory with a cubic variation of in-plane displacements according to the thickness and linear/quadratic transverse displacement is presented. The solution achieved in the trigonometric series form and rests on the Green's function method. Two porosity types and their influence on material properties, and mechanical behavior are considered. The network of pores is assumed to be empty or filled with low-pressure air, and the material properties are calculated using the power-law distribution idealization. Numerical calculations have been carried out to demonstrate the accuracy of the kinematic model for the dynamic problem, the effect of porosity, thickness of porous layers, power-law index, and type of loading on the dynamic response of an imperfect functionally graded material plate.

Key Words
functionally graded plate; porous; refined third-order shear deformation theory; dynamic response; timedependent load

Address
Nadiia V. Dergachova and Guangping Zou: School of Aerospace and Civil Engineering, Harbin Engineering University, 145 Nantong Street, Harbin 150001, PR China

Abstract
Existing meso-scale models of concrete need to refine the mesh grids of aggregate and cement mortar, which may greatly reduce the computational efficiency. To overcome this problem, a novel meso-scale modeling strategy, which is based on rigid body spring method and Voronoi diagram, is proposed in this study to establish the meso-scale model of concrete. Firstly, establish numerical aggregate models according to user-defined programs. Circle aggregates are adopted due to their high efficiency in generation and packing process, and the grading of aggregate are determined according to the distribution curve proposed by Full and Thompson; Secondly, extract the centroids of aggregates, and then develop the Voronoi diagram in which aggregate centroids are defined as initial scatters; Finally, establish the rigid body spring model for concrete based on the Voronoi diagram. Aggregates are represented by rigid blocks, and assumed to be unbreakable. Cement mortar is concentrated into the interface between adjacent blocks and represented by two uniform springs. The number of grids is consistent with that of aggregates in specimens, and no mesh-refinement of aggregates and cement mortar is required. The accuracy and efficiency of the proposed modeling strategy are firstly identified by comparing the numerical results with the experimental ones, and then the applicability of the proposed strategy with different volume percentage occupied by aggregates is investigated.

Key Words
concrete; numerical aggregate; meso-scale model; rigid body spring model; Voronoi diagram

Address
Chao Zhao, Zheng Shi and Xingu Zhong: Hunan Provincial Key Laboratory of Structures for Wind Resistance and Vibration Control & School of Civil Engineering, Hunan University of Science and Technology, Taoyuan Road, Yuhu District, Xiangtan, China


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