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CONTENTS
Volume 23, Number 1, January 2019
 

Abstract
The use of non-linear analysis of structures in a functional way for evaluating the structural seismic behavior has attracted the attention of the engineering community in recent years. The most commonly used functional method for analysis is a non-linear static method known as the \"pushover method\". In this study, for the first time, a cyclic pushover analysis with different loading protocols was used for seismic investigation of curved bridges. The finite element model of 8-span curved bridges in plan created by the ZEUS-NL software was used for evaluating different pushover methods. In order to identify the optimal loading protocol for use in astatic non-linear cyclic analysis of curved bridges, four loading protocols (suggested by valid references) were used. Along with cyclic analysis, conventional analysis as well as adaptive pushover analysis, with proven capabilities in seismic evaluation of buildings and bridges, have been studied. The non-linear incremental dynamic analysis (IDA) method has been used to examine and compare the results of pushover analyses. To conduct IDA, the time history of 20 far-field earthquake records was used and the 50% fractile values of the demand given the ground motion intensity were computed. After analysis, the base shear vs displacement at the top of the piers were drawn. Obtained graphs represented the ability of a cyclic pushover analysis to estimate seismic capacity of the concrete piers of curved bridges. Based on results, the cyclic pushover method with ISO loading protocol provided better results for evaluating the seismic investigation of concrete piers of curved bridges in plan.

Key Words
curved bridges; pushover analysis; cyclic loading; incremental dynamic analysis

Address
Hamid Reza Ahmadi: Department of Civil Engineering, Faculty of Engineering, University of Maragheh, Maragheh, P.O. Box 55136-553, Iran
Nariman Namdari: Department of Civil Engineering, Bandar Abbas Branch, Islamic Azad University, Bandar Abbas, Iran
Maosen Cao: Department of Engineering Mechanics, Hohai University, 210098 Nanjing, Jiangsu, People\'s Republic of China
Mahmoud Bayat: Department of Civil and Environmental Engineering, University of Pittsburgh, 3700 O\'Hara Street, 729 Benedum Hall, Pittsburgh, PA 15261, USA

Abstract
Nowadays, the characterization of Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) tensile behavior still remains a challenge for researchers. For this purpose, a simplified closed-form non-linear hinge model based on the Third Point Bending Test (ThirdPBT) was developed by the authors. This model has been used as the basis of a simplified inverse analysis methodology to derive the tensile material properties from load-deflection response obtained from ThirdPBT experimental tests. In this paper, a non-linear finite element model (FEM) is presented with the objective of validate the closedform non-linear hinge model. The state determination of the closed-form model is straightforward, which facilitates further inverse analysis methodologies to derive the tensile properties of UHPFRC. The accuracy of the closed-form non-linear hinge model is validated by a robust non-linear FEM analysis and a set of 15 Third-Point Bending tests with variable depths and a constant slenderness ratio of 4.5. The numerical validation shows excellent results in terms of load-deflection response, bending curvatures and average longitudinal strains when resorting to the discrete crack approach.

Key Words
finite element model; numerical validation; ultra-high performance fiber-reinforced concrete; closed-form non-linear hinge model; third point bending test; smeared cracking approach; discrete cracking approach

Address
Eduardo J. Mezquida-Alcaraz, Juan Navarro-Gregori, Juan Ángel Lopez and Pedro Serna-Ros: Instituto de Ciencia y Tecnología del Hormigón (ICITECH), Universitat Politècnica de Valencia, Camino de Vera s/n, 46022, Valencia, Spain

Abstract
In this paper, an algorithm is presented to simulate numerically the reinforced concrete (RC) columns having any geometric form of section, loaded eccentrically along one or two axes. To apply the algorithm, the columns are discretized into two macro-elements (MEs) globally and the critical sections of columns are discretized into fixed rectangular finite elements locally. A proposed triple simultaneous dichotomy convergence method is applied to find the equilibrium state in the critical section of the column considering the three strains at three corners of the critical section as the main characteristic variables. Based on the proposed algorithm a computer program has been developed for simulation of the nonlinear behavior of the eccentrically-loaded columns. A good agreement has been witnessed between the results obtained applying the proposed algorithm and the experimental test results. The simulated results indicate that the ultimate strength and stiffness of the RC columns increase with the increase in axial force value, but large axial loads reduce the ductility of the column, make it brittle, impose great loss of material, and cause early failure.

Key Words
reinforced concrete; columns; simulation; monotonic; cyclic; eccentrically-loaded

Address
Kabir Sadeghi and Fatemeh Nouban: Civil and Environmental Engineering Faculty, Near East University, Near East Boulevard, ZIP: 99138, Nicosia, North Cyprus, via Mersin 10, Turkey

Abstract
In view of the increasing utility of concrete as a construction material, the major challenge is to improve the quality of construction. Nowadays the common problem faced by many of the concrete plants is the shortage of river sand as fine aggregate material. This led to the utilization of locally available materials from quarries as fine aggregate. With the percentage of fines present in Crushed Rock Fines (CRF)or crushed sand is more compared to river sand, it shows a better performance in terms of fresh properties. The present study deals with the formulation of SCC mix design based on the chosen plastic viscosity of the mix and the measured plastic viscosity of cement pastes incorporating supplementary cementitious materials with CRF and river sand as a fine aggregate. Four different combinations including two binary and one ternary mix are adopted for the current study. Influence of plastic viscosity of the mix on the fresh and hardened properties are investigated for SCC mixes with varying water to cement ratios. It is observed that for an increasing plastic viscosity of the mix, slump flow, T500 and J-ring spread increased but V-funnel and L-box decreased. Compressive, split tensile and flexural strengths decreased with the increase in plastic viscosity.

Key Words
crushed rock fines; Self-Compacting Concrete; plastic viscosity; compressive strength; mix design; GGBS; fly ash

Address
J.S. Kalyana Rama, Sai Kubair and A. Vasan: Department of Civil Engineering, BITS Pilani, Hyderabad Campus, Hyderabad, India
M.V.N. Sivakumar: Department of Civil Engineering, National Institute of Technology, Warangal, India

Abstract
In recent years, multiple experimental studies have been performed on using fiber reinforced polymer (FRP) bars in reinforced concrete (RC) structural members. FRP bars provide a new type of reinforcement that avoids the corrosion of traditional steel reinforcement. In this study, predicting the shear strength of RC beams with FRP longitudinal bars using artificial neural networks (ANNs) is investigated as a different approach from the current specific codes. An ANN model was developed using the experimental data of 104 FRP-RC specimens from an existing database in the literature. Seven different input parameters affecting the shear strength of FRP bar reinforced RC beams were selected to create the ANN structure. The most convenient ANN algorithm was determined as traingdx. The results from current codes (ACI440.1R-15 and JSCE) and existing literature in predicting the shear strength of FRP-RC beams were investigated using the identical test data. The study shows that the ANN model produces acceptable predictions for the ultimate shear strength of FRP-RC beams (maximum R2≈0.97). Additionally, the ANN model provides more accurate predictions for the shear capacity than the other computed methods in the ACI440.1R-15, JSCE codes and existing literature for considering different performance parameters.

Key Words
internal FRP bar; reinforced concrete; beam; shear strength; artificial neural network

Address
Gunnur Yavuz: Department of Civil Engineering, Faculty of Engineering and Natural Sciences, Konya Technical University, Konya, Turkey

Abstract
This paper presents a computational rational model to predict the ultimate and optimized load capacity of reinforced concrete (RC) beams strengthened by a combination of longitudinal and transverse fiber reinforced polymer (FRP) composite plates/sheets (flexure and shear strengthening system). Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/ rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. A high performance concrete, known as polymer concrete, made up of natural aggregates and an orthophthalic polyester binder, reinforced with non-metallic bars (glass reinforced polymer) has been studied. The material is described at micro and macro level, presenting the key physical and mechanical properties using different experimental techniques. Furthermore, a full description of non-metallic bars is presented to evaluate its structural expectancies, embedded in the polymer concrete matrix. In this paper, the mechanism of mechanical interaction of smooth and lugged FRP rods with concrete is presented. A general modeling and application of various elements are demonstrated. The contact parameters are defined and the procedures of calculation and evaluation of contact parameters are introduced. The method of calibration of the calculated parameters is presented. Finally, the numerical results are obtained for different bond parameters which show a good agreement with experimental results reported in literature.

Key Words
fiber-reinforced polymers; reinforced concrete (FRP); mechanical interaction; bond; contact; friction

Address
Khosro Shahpoori Arani: Department of Civil Engineering, Qeshm International Branch, Islamic Azad University, Qeshm, Iran
Yousef Zandi: Department of Civil Engineering, Tabriz Branch, Islamic Azad University, Tabriz, Iran
Binh Thai Pham: Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam
M.A. Mu\\\'azu: Department of Civil Engineering, Jubail University College, Royal Commission of Jubail and Yanbu, Jubail, Saudi Arabia
Javad Katebi: Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran
Mohammad Mohammadhassani: Seismology Engineering & Risk Department, Road, Housing & Urban Development Research Center (BHRC), Tehran, Iran
Seyedamirhesam Khalafi: Department of Construction Management, University of Houston, USA
Edy Tonnizam Mohamad: Centre of Tropical Geoengineering (GEOTROPIK), Faculty of Civil Engineering, Universiti Teknologi Malaysia, Johor Bahru, Malaysia
Karzan Wakil: Research Center, Sulaimani Polytechnic University, Sulaimani 46001, Kurdistan Region, Iraq
Majid Khorami: Facultad de Arquitectura y Urbanismo, Universidad UTE, Calle Rumipamba s/n y Bourgeois, Quito, Ecuador

Abstract
Modeling approach for mesoscopic model of concrete depicting mass transportation and physicochemical reaction is important since there is growing demand for accuracy and computational efficiency of numerical simulation. Mesoscopic numerical simulation considering binder, aggregate and interfacial transition zone (ITZ) generally produces huge number of DOFs, which is inapplicable for full structure. In this paper, a three-dimensional multiscale approach describing three-phase structure of concrete was discussed numerically. An effective approach generating random aggregate in polygon based on checking centroid distance and intersection of line segment was introduced. Moreover, ITZ elements were built by parallel expanding the surface of aggregates on inner side. By combining mesoscopic model including full-graded aggregate and macroscopic model, cases related to diffusivity and thickness of ITZ, volume fraction and grade of aggregate were studied regarding the consideration of multiscale compensation. Result clearly showed that larger analysis model in multiscale model expanded the diffusion space of chloride ion and decreased chloride content in front of rebar. Finally, this paper addressed some worth-noting conclusions about the chloride distribution and rebar corrosion regarding the configuration of, rebar diameter, concrete cover and exposure period.

Key Words
reinforced concrete structure; chloride diffusion; numerical simulation; multiscale; ITZ

Address
Xi Tu, Cunjun Pang and Xuhong Zhou: Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, China; College of Civil Engineering, Chongqing University, Chongqing, China
Airong Chen: Department of Bridge Engineering, Tongji University, Shanghai, China


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