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CONTENTS
Volume 21, Number 1, January 2018
 

Abstract
Electrical resistivity is a property associated with both the physical and chemical characteristics of concrete. It allows the evaluation of the greater or lesser difficulty with which aggressive substances penetrate the concrete\'s core before the dissolution of the passive film process and the consequent reinforcement\'s corrosion begin. This work addresses the steel fiber addition to concrete with two types and various contents from 0% to 1.3%, correlating it with its electrical resistivity. To that effect, 9 different mixes of steel fiber reinforced concrete (SFRC) were produced. The electrical resistivity was evaluated on the on six years aged SFRC by direct measurement at different frequency from 0.1 kHz to 100 kHz. The results indicate that steel fiber content is strongly conditioned by the type and quantity of the additions used. It was also found that long type of fibers has more effect on decreasing the electrical resistivity of concrete than short fibers. Therefore, they increase the corrosion risk of concrete depending on fiber volume fraction and moisture percentage.

Key Words
steel fiber; old-concrete; electrical resistivity; carbonation

Address
Tayfun Uygunoglu: Engineering Faculty, Civil Engineering Department, Afyon Kocatepe University, 03200, Afyonkarahisar, Turkey
Ilker Bekir Topcu: Engineering-Architectural Faculty, Civil Engineering Department, Eskişehir Osmangazi University, 26480, Eskişehir, Turkey
Baris Simsek: Faculty of Engineering, Department of Chemical Engineering, Çank

Abstract
The possibilities of non-linear analysis of reinforced-concrete structures are under development. In particular, current research areas include structural analysis with the application of advanced computational and material models. The submitted article aims to evaluate the possibilities of the determination of material properties, involving the tensile strength of concrete, fracture energy and the modulus of elasticity. To evaluate the recommendations for concrete, volume computational models are employed on a comprehensive series of tests. The article particularly deals with the issue of the specific properties of fracture-plastic material models. This information is often unavailable. The determination of material properties is based on the recommendations of Model Code 1990, Model Code 2010 and specialized literature. For numerical modelling, the experiments with the so called \"classic\" concrete beams executed by Bresler and Scordelis were selected. It is also based on the series of experiments executed by Vecchio. The experiments involve a large number of reinforcement, cross-section and span variants, which subsequently enabled a wider verification and discussion of the usability of the non-linear analysis and constitutive concrete model selected.

Key Words
reinforced concrete; classic beams; material properties; three-point bending test; computational mechanics

Address
Oldrich Sucharda and Petr Konecny: Faculty of Civil Engineering, VŠB-Technical University of Ostrava, Ludvíka Podéště 1875/17, 708 33 Ostrava-Poruba, Czech Republic

Abstract
In this study, we analyze the behavior of concrete which contains zeolite and diatomite. In order to achieve the goal, we utilize expert system methods. The utilized methods are artificial neural network and adaptive network-based fuzzy inference systems. In this respect, we exploit seven different mixes of concrete. The concrete mixes contain zeolite, diatomite, mixture of zeolite and diatomite. All seven concrete mixes are exposed to 28, 56 and 90 days\' compressive strength experiments with 63 specimens. The results of the compressive strength experiments are used as input data during the training and testing of expert system methods. In terms of artificial neural network and adaptive network-based fuzzy models, data format comprises seven input parameters, which are; the age of samples (days), amount of Portland cement, zeolite, diatomite, aggregate, water and hyper plasticizer. On the other hand, the output parameter is defined as the compressive strength of concrete. In the models, training and testing results have concluded that both expert system model yield thrilling medium to predict the compressive strength of concrete containing zeolite and diatomite.

Key Words
expert systems; compressive strength; concrete; zeolite; diatomite

Address
Giyasettin Ozcan: Department of Computer Engineering, Faculty of Engineering, Uludag University, Bursa, Turkey
Yilmaz Kocak: Department of Construction, Kutahya Vocational School of Technical Sciences, Dumlupinar University, Kutahya, Turkey
Eyyup Gulbandilar: Department of Computer Engineering, Faculty of Engineering and Architecture, Eskisehir Osmangazi University, Eskisehir, Turkey

Abstract
This paper deals with the stability analysis of concrete pipes mixed with nanoparticles conveying fluid. Instead of cement, the Fe2O3 nanoparticles are used in construction of the concrete pipe. The Navier-Stokes equations are used for obtaining the radial force of the fluid.Mori-Tanaka model is used for calculating the effective material properties of the concrete pipe-Fe2O3 nanoparticles considering the agglomeration of the nanoparticles. The first order shear deformation theory (FSDT) is used for mathematical modeling of the structure. The motion equations are derived based on energy method and Hamilton\'s principal. An exact solution is used for stability analysis of the structure. The effects of fluid, volume percent and agglomeration of Fe2O3 nanoparticles, magnetic field and geometrical parameters of pipe are shown on the stability behaviour of system. Results show that considering the agglomeration of Fe2O3 nanoparticles, the critical fluid velocity of the concrete pipe is decreased.

Key Words
concrete pipe; Fe2O3 nanoparticles; conveying fluid; stability; agglomeration

Address
Alireza Zamani Nouri: Department of Civil Engineering, College of Engineering, Saveh Branch, Islamic Azad University, Saveh, Iran

Abstract
With the increase in industrialization and urbanization, growing demand has enhanced rate of new constructions and old demolitions. To avoid serious environmental impacts and hazards recycled concrete aggregates (RCA) is being adopted in all over the world. This paper investigates successive recycled coarse aggregates (SRCA) in which old concrete made with RCA in form of concrete cubes was used. The cubes were crushed to prepare new concrete using aggregates from crushing of old concrete, used as SRCA. The mechanical behavior of concrete was determined containing SRCA; the properties of SRCA were evaluated and then compared with natural aggregates (NA). Replacement of NA with SRCA in ratio upto 100% by weight was studied for workability, mechanical properties and microstructural analysis. It was observed that with the increase in replacement ratio workability and compressive strength decreased but in acceptable limits so SRCA can be used in low strength concretes rather than high strength concrete structures.

Key Words
successive recycled coarse aggregate; waste; fly ash strength; scanning electron microscope; X-ray diffraction

Address
Deepankar K. Ashish: Department of Civil Engineering, Maharaja Agrasen University, Baddi 174103, India; Department of Civil Engineering, Punjab Engineering College (Deemed to be University), Chandigarh 160012, India
Preeti Saini: Department of Civil Engineering, Kurukshetra University, Kurukshetra 136119, India

Abstract
Artificial neural network models can be successfully used to simulate the complex behavior of many problems in civil engineering. As compared to conventional computational methods, this popular modeling technique is powerful when the relationship between system parameters is intrinsically nonlinear, or cannot be explicitly identified, as in the case of concrete behavior. In this investigation, an artificial neural network model was developed to assess the residual compressive strength of self-compacted concrete at elevated temperatures (20-900oC) and various relative humidity conditions (28-99%). A total of 332 experimental datasets, collected from available literature, were used for model calibration and verification. Data used in model development incorporated concrete ingredients, filler and fiber types, and environmental conditions. Based on the feed-forward back propagation algorithm, systematic analyses were performed to improve the accuracy of prediction and determine the most appropriate network topology. Training, testing, and validation results indicated that residual compressive strength of selfcompacted concrete, exposed to high temperatures and relative humidity levels, could be estimated precisely with the suggested model. As illustrated by statistical indices, the reliability between experimental and predicted results was excellent. With new ingredients and different environmental conditions, the proposed model is an efficient approach to estimate the residual compressive strength of self-compacted concrete as a substitute for sophisticated laboratory procedures.

Key Words
modeling; artificial neural network; residual compressive strength; self-compacted concrete; temperature; relative humidity

Address
Ahmed M. Ashteyat: Department of Civil Engineering, The University of Jordan, Amman 11942, Jordan
Muhannad Ismeik: Department of Civil Engineering, The University of Jordan, Amman 11942, Jordan; Department of Civil Engineering, Australian College of Kuwait, Safat 13015, Kuwait

Abstract
A large main shock may consist of numerous aftershocks with a short period. The aftershocks induced by a large main shock can cause the collapse of a structure that has been already damaged by the preceding main shock. These aftershocks are important factors in structural damages. Furthermore, despite what is often assumed in seismic design codes, earthquakes do not usually occur as a single event, but as a series of strong aftershocks and even fore shocks. For this reason, this study investigates the effect and potential of consecutive earthquakes on the response and behavior of concrete structures. At first, six moment resisting concrete frames with 3, 5, 7, 10, 12 and 15 stories are designed and analyzed under two different records with seismic sequences from real and artificial cases. The damage states of the model frames were then measured by the Park and Ang\'s damage index. From the results of this investigation, it is observed that the sequences of ground motions can almost double the accumulated damage and increased response of structures. Therefore, it is certainly insufficient to ignore this effect in the design procedure of structures. Also, the use of artificial seismic sequences as design earthquake can lead to non-conservative prediction of behavior and damage of structures under real seismic sequences.

Key Words
seismic sequence; damage index; cumulative damage; reinforced concrete structures

Address
Gholamreza Ghodrati Amiri and Elham Rajabi: Center of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran


Abstract
A differential scheme based micromechanical framework is proposed to obtain the effective properties of the saturated concrete repaired by the electrochemical deposition method (EDM) considering the interfacial transition zone (ITZ) effects. The constituents of the repaired concrete are treated as different phases, consisting of (micro-)cracks, (micro-)voids and (micro-)pores (occupied by water), deposition products, intrinsic concrete made up by the three traditional solid phases (i.e., mortar, coarse aggregates and their interfaces) and the ITZs. By incorporating the composite sphere assemblage (CSA) model and the differential approach, a new multilevel homogenization scheme is utilized to quantitatively estimate the mechanical performance of the repaired concrete with the ITZs. The CSA model is modified to obtain the effective properties of the equivalent particle, which is a three-phase composite made up of the water, deposition products and the ITZs. The differential scheme is employed to reach the equivalent composite of the concrete repaired by EDM considering the ITZ effects. Moreover, modification procedures considering the ITZ effects are presented to attain the properties of the repaired concrete in the dry state. Results in this study are compared with those of the existing models and the experimental data. It is found that the predictions herein agree better with the experimental data than the previous models.

Key Words
electrochemical deposition; healing; saturated concrete; interfacial transition zone; effective properties; differential scheme; micromechanical framework

Address
Qing Chen: Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Tongji University, 4800 Cao

Abstract
To improve the design equation for the evaluation of the bursting force in the post-tensioned anchorage zone, this paper presents the analyses and design of the post-tensioned (PT) anchorage zone on the basis of three dimensional (3D) finite element (FE) analyses. The structural behavior was investigated through linear elastic finite element analyses upon consideration of the change in design parameters such as the bearing plate size, the eccentricity, and the tendon inclination. Moreover, consideration of the duct hole, which causes an increase of the bursting stress with a change in its distribution along the anchorage zone as well, is emphasized. Since that an exact prediction of the bursting force is the primary interest in design practice, additional parametric analyses are carried out to evaluate the relative contribution of all design parameters in determining the bursting force, and a comparison with the design guidelines mentioned in AASHTO-LRFD has been provided. Finally, an improved design guideline that takes into account the influence by the duct hole is suggested.

Key Words
anchorage zone; bursting force; duct hole; local zone; design guideline

Address
Joung Rae Kim and Hyo-Gyoung Kwak: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701, Republic of Korea

Abstract
This paper presents the results of an experimental study to investigate the influences of high temperatures on the mechanical properties of concrete containing recycled fine aggregate. A total of 150 concrete prisms (100x100x100 mm) are cast and heated under five different temperatures (20oC, 200oC, 400oC, 600oC, 800oC ) for test. The results show that the mass loss, compressive strength, elastic modulus, splitting tensile strength of concrete specimens containing recycled fine aggregate decline significantly as the temperature rise. At the same temperature, the compressive strength, splitting tensile strength, elastic modulus of concrete specimens containing recycled coarse aggregate and recycled fine aggregate (RHC) is lower than that of concrete specimens containing natural coarse aggregate and recycled fine aggregate (RFC). The shape of stress–strain curves of concrete specimens at different temperatures is different, and the shape of that become flatter as the temperature rises. Normal concrete has better energy absorption capacity than concrete containing recycled fine aggregate.

Key Words
recycled fine aggregate; concrete; elastic modulus; temperature; strength

Address
Jiong-Feng Liang: State Key Laboratory Breeding Base of Nuclear Resources and Environment, East China Institute of Technology, Nanchang, P.R. China; Faculty of Civil and Architecture Engineering, East China Institute of Technology, Nanchang, P.R. China
En Wang, Xu Zhou and Qiao-Li Le: Faculty of Civil and Architecture Engineering, East China Institute of Technology, Nanchang, P.R. China

Abstract
Reinforced concrete corbel beams (span to depth ratio of a corbel is less than one) are designed with primary reinforcement bars to account for bending moment and with the secondary reinforcement placed parallel to the primary reinforcement (shear stirrups) to resist shear force. It is interesting to note that most of the available analytical procedures employ empirical formulas for the analysis of reinforced concrete corbels. In the present work, a generalized and a simple strut and tie models were employed for the analysis of reinforced corbel beams. The models were benchmarked against experimental results available in the literature. It was shown here that increase of shear stirrups increases the load carrying capacity of reinforced concrete corbel beams. The effect of horizontal load on the load carrying capacity of the corbel beams has also been examined in the present paper. It is observed from the strut and tie models that the resistance of the corbel beam subjected to combined horizontal and vertical load did not change with increase in shear stirrups if the failure of the corbel is limited by concrete crushing. In other words, the load carrying capacity was independent of the horizontal load when failure of the beam occurred due to concrete crushing.

Key Words
reinforced concrete; strut and tie; corbel beam

Address
Jafarali Parol, Jamal Al-Qazweeni and Safaa Abdul Salam: Sustainability and Reliability of Infrastructures Program, Energy and Building Research Center, Kuwait Institute for Scientific Research, Kuwait

Abstract
This study introduces the supervised committee fuzzy model as a hybrid fuzzy model to predict compressive strength (CS) of geopolymers prepared from alumina-silica products. For this purpose, more than 50 experimental data that evaluated the effect of Al2O3/SiO2, Na2O/Al2O3, Na2O/H2O and Na/[Na+K] on (CS) of geopolymers were collected from the literature. Then, three different Fuzzy Logic (FL) models (Sugeno fuzzy logic (SFL), Mamdani fuzzy logic (MFL), and Larsen fuzzy logic (LFL)) were adopted to overcome the inherent uncertainty of geochemical parameters and to predict CS. After validating the model, it was found that the SFL model is superior to MFL and LFL models, but each of the FL models has advantages to predict CS. Therefore, to achieve the optimal performance, the supervised committee fuzzy logic (SCFL) model was developed as a hybrid method to combine the benefits of individual FL models. The SCFL employs an artificial neural network (ANN) model to re-predict the CS of three FL model predictions. The results also show significant fitting improvement in comparison with individual FL models.

Key Words
compressive strength; geopolymer; fuzzy model; Artificial Neural Network (ANN); Supervised Committee Fuzzy Logic (SCFL)

Address
Ata Allah Nadiri: Department of Earth Sciences, Faculty of Natural Science, University of Tabriz, 29 Bahman Boulevard, Tabriz, East Azarbaijan, Iran
Somayeh Asadi: Department of Architectural Engineering, Pennsylvania State University, 104 Engineering, Unit A, University Park, PA 16802, USA
Hamed Babaizadeh: LADOTD, 1201 Capitol Access Road, Baton Rouge, LA 70802, USA
Keivan Naderi: Department of Earth Sciences, Faculty of Natural Science, University of Tabriz, 29 Bahman Boulevard, Tabriz, East Azarbaijan, Iran


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