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CONTENTS
Volume 25, Number 2, February 2020
 

Abstract
This paper aims to analytically study the effect of loading conditions and confinement type on the mechanical properties of the concrete-steel composite columns under axial compressive loading. The axial loading is applied to the composite columns in the two ways; only on the concrete core, and on the concrete core and steel tube simultaneously, which are called steel tube-confined concrete (STCC) and concrete-filled steel tube (CFST) columns, respectively. In addition, the confinement is investigated in the three types of passive, short-term active and long-term active confinement. Nonlinear finite element 3D models for analyzing these columns are developed using the ABAQUS program, and then these models are verified with respect to the recent experimental results reported by the authors on the STCC and CFST columns experiencing active and passive confinements. Axial and lateral stress-strain curves as well as the failure mode for qualitative verification, and compressive strength for quantitative verification are considered. It is found that there is a good consistency between the finite element analysis results and the experimental ones. In addition, a parametric study is performed to evaluate the effect of axial loading type, prestressing ratio, concrete compressive strength and steel tube diameter-to-wall thickness ratio on the compressive behavior of the composite columns. Finally, the compressive strength results of CFST specimens obtained via the finite element analysis are compared with the values specified by the international codes and standards including EC4, CSA, ACI-318, and AISC, with the results showing that ACI-318 and AISC underestimate the compressive strength of the composite columns, while EC4 and CSA codes present overestimated values.

Key Words
finite element modeling; active confinement; loading conditions; composite column; STCC; CFST; codes

Address
Mahdi Nematzadeh and Saeed Fazli: Department of Civil Engineering, University of Mazandaran, Babolsar, Iran

Abstract
The construction field must always explore sustainable ways of using its raw materials. Studying the environmental impact generated by reinforced concrete raw materials during their production and transportation can contribute to reducing this impact. This paper initially presents the carbon dioxide emissions from reinforced concrete raw materials, quantified per kilo of raw material and per cubic meter of concrete with different characteristic strengths, for southern Brazil. Subsequently, reinforced concrete elements were optimized to minimize their environmental impact and cost. It was observed that lower values of carbon dioxide emissions and cost savings are generated for less resistant concrete when the structural element is a beam, and that reductions in the cross section dimensions of the beams, sized based on the use of higher strength concrete, may not compensate for the increased environmental impact and costs. For the columns, the behavior differed, presenting lower values of carbon dioxide emissions and costs for higher concrete strengths. The proposed methodology, as well as the results obtained, can be used to support structural projects that have less impact on the environment.

Key Words
environmental impact; reinforced concrete; CO2 emission; optimization; structures

Address
Jair F. Santoro: Faculty of Engineering, Sul-Rio-Grandense Federal Institute, 99064-440, Passo Fundo, Brazil
Moacir Kripka: Civil and Environmental Engineering Graduate Program, University of Passo Fundo, 99052-900, Passo Fundo, Brazil

Abstract
There is a growing interest in the use of by-product materials such as ceramics as alternative materials in construction. The aim of this study is to investigate the mechanical properties and durability of sustainable concrete containing waste ceramic powder (WCP), and to predict the results using artificial neural network (ANN). In this order, different water to binder (W/B) ratios of 0.3, 0.4, and 0.5 were considered, and in each W/B ratio, a percentage of cement (between 5-50%) was replaced with WCP. Compressive and tensile strengths, water absorption, electrical resistivity and rapid chloride permeability (RCP) of the concrete specimens having WCP were evaluated by related experimental tests. The results showed that by replacing 20% of the cement by WCP, the concrete achieves compressive and tensile strengths, more than 95% of those of the control concrete, in the long term. This percentage increases with decreasing W/B ratio. In general, by increasing the percentage of WCP replacement, all durability parameters are significantly improved. In order to validate and suggest a suitable tool for predicting the characteristics of the concrete, ANN model along with various multivariate regression methods were applied. The comparison of the proposed ANN with the regression methods indicates good accuracy of the developed ANN in predicting the mechanical properties and durability of this type of concrete. According to the results, the accuracy of ANN model for estimating the durability parameters did not significantly follow the number of hidden nodes.

Key Words
high performance sustainable concrete; waste ceramic powder; mechanical properties; durability; ANN

Address
Babak Behforouz, Parham Memarzadeh, Farshid Fathi: Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran
Mohammadreza Eftekhar: Department of Civil Engineering, Isfahan University of Technology (IUT), Isfahan, Iran

Abstract
This paper aims to study vibration characteristics of chiral and zigzag double-walled carbon nanotubes entrenched on Donnell shell model. The Eringen\'s nonlocal elastic equations are being combined with Donnell shell theory to observe small scale response. Wave propagation is proposed technique to establish field equations of model subjected to four distinct end supports. A nonlocal model has been formulated to explore the frequency spectrum of both chiral and zigzag double-walled CNTs along with diversity of indices and nonlocal parameter. The significance of scale effect in relevance of length-to-diameter and thickness- to- radius ratios are discussed and displayed in detail. The numerical solution based on this nonlocal Donnell shell model can be further used to predict other frequency phenomena of double-walled and multi-walled CNTs.

Key Words
CNT; Chiral and zigzag; nonlocal parameter; Donnell shell model

Address
Sehar Asghar, Muhammad N. Naeem, Muzamal Hussain: 1Department of Mathematics, Govt. College University Faisalabad, 38040, Faisalabad, Pakistan
Muhammad Taj: Department of Mathematics, University of Azad Jammu and Kashmir, Muzaffarabad, 1300, Azad Kashmir, Pakistan
Abdelouahed Tounsi: Materials and Hydrology Laboratory, University of SidiBel Abbes, Algeria 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

Abstract
For the influence of the propagation law of stress wave at the coal-rock interface during the pre-blasting of the top coal in top coal mining, the ANSYS-LS/DYNA fluid-solid coupling algorithm was used to numerical calculation and the lifedeath element method was used to simulate the propagation of explosion cracks. The equation of the crushing zone and the fracturing zone were derived. The results were calculated and showed that the crushing radius is 14.6 cm and the fracturing radius is 35.8 cm. With the increase of the angles between the borehole and the coal-rock interface, the vibration velocity of the coal particles and the rock particles at the interface decreases gradually, and the transmission coefficient of the stress wave from the coal mass into the rock mass decreases gradually. When the angle between the borehole and the coal-rock interface is 0o, the overall crushing degree is about 11% and up to the largest. With the increase of the distance from the charge to the coal-rock interface, the stress wave transmission coefficient and the crushing degree of the coal-rock are gradually decreased. At the distance of 50 cm, the crushing degree of the coal-rock reached the maximum of approximately 12.3%.

Key Words
coal-rock interface; stress wave; crushing degree; transmission coefficient

Address
Fei Liu: Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization, Institute of Deep Earth Sciences and Green Energy, College of Civil and Transportation Engineering, Shenzhen University, Shenzhen, 518060, China
Lianghui Li: College of Energy & Mining, China University of Mining & Technology, Beijing 100083, China

Abstract
In this work, the buckling and vibrational behavior of the composite beam armed with single-walled carbon nanotubes (SW-CNT) resting on Winkler-Pasternak elastic foundation are investigated. The CNT-RC beam is modeled by a novel integral first order shear deformation theory. The current theory contains three variables and uses the shear correction factors. The equivalent properties of the CNT-RC beam are computed using the mixture rule. The equations of motion are derived and resolved by Applying the Hamilton\'s principle and Navier solution on the current model. The accuracy of the current model is verified by comparison studies with others models found in the literature. Also, several parametric studies and their discussions are presented.

Key Words
buckling; dynamic behaviour; SW-CNT; Hamilton

Address
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: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia; Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Departement des Sciences et de la Technologie, centre universitaire de Tissemsilt, BP 38004 Ben Hamouda, Algerie
S.R. Mahmoud: GRC Department, Jeddah Community College, King Abdulaziz University, Jeddah, Saudi Arabia
Abdeldjebbar Tounsi: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria
Ali Algarni: Statistics Department, Faculty of Science, King Abdulaziz University, Jeddah, Kingdom of 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: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia; Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria

Abstract
Optimal design of structures against earthquake loads is often limited to reduce initial construction costs, while the cost induced to structures during their useful life may be several times greater than the initial costs. Therefore, it is necessary to consider the indirect costs due to earthquakes in the design process. In this research, an integrated methodology for calculating life cycle cost (LCC) of moment-resisting concrete frames is presented. Increasing seismic safety of structures and reducing human casualties can play an important role in determining the optimal design. Costs incurred for structures are added to the costs of construction, including the costs of reconstruction, financial losses due to the time spent on reconstruction, interruption in building functionality, the value of people\'s life or disability, and content loss are a major part of the future costs. In this research, fifty years of useful life of structures from the beginning of the construction is considered as the life cycle. These costs should be considered as factors of calculating indirect costs of a structure. The results of this work represent the life cycle cost of a 4 story, 7 story, and 10 story moment-resisting concrete frame by details. This methodology is developed based on the economic conditions of Iran in 2016 and for the case of Tehran city.

Key Words
quantitative risk; seismic design; optimal design; life cycle cost; indirect costs; financial losses; concrete structures

Address
Mohammadhassan Hassani, Behrouz Behnam and Reza Maknoon: School of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran

Abstract
Nowadays, steel fiber reinforced concretes (SFRCs) are widely used in practical applications. Significant experimental research has thus been carried out to determine the constitutive equations that represent the behavior of SFRCs under multiaxial loadings. However, numerical modelling of SFRCs via FEM has been challenging due to the complexities of the implementation of these constitutive equations. In this study, following the literature, a plasticity model is constructed for the behavior of SFRCs that involves the Willam-Warnke failure surface with the relevant evolution laws and a non-associated flow rule for determining the plastic deformations. For the precise (yet rapid) integration of the constitutive equations, an explicit substepping scheme consisting of yield intersection and drift correction algorithms is employed and thus implemented in ABAQUS via UMAT. The FEM model includes various material parameters that are determined from the experimental data. Three sets of parameters are used in the numerical simulations. While the first set is from the experiments that are conducted in this study on SFRC specimens with various contents of steel fibers, the other two sets are from the experiments reported in the literature. The response of SFRCs under multiaxial compression obtained from various numerical simulations are compared with the experimental data. The good agreement between numerical results and the experimental data indicates that not only the adopted plasticity model represents the behavior of SFRCs very well but also the implemented integration scheme can be employed in practical applications of SFRCs.

Key Words
steel fiber reinforced concrete (SFRC); finite element method (FEM); concrete constitutive models; nonlinear analysis; software development and applications

Address
Gholamreza B. Golpasand, Masood Farzam and Siamak S. Shishvan: Department of Structural Engineering, University of Tabriz, Tabriz, Iran

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