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CONTENTS
Volume 19, Number 3, March 2017
 

Abstract
This paper describes an experimental study of the cyclic performance of concrete beams reinforced with CFRP prestressed concrete prisms (PCP). The failure modes, hysteretic loops, skeleton curve, ductility, energy dissipation capacity and stiffness degradation of concrete beams reinforced with CFRP prestressed concrete prisms were analyzed. The results show that The CFRP prestressed prisms reinforced concrete beams have good seismic performance. The level of effective prestress and cross section of CFRP prestressed prisms had a little influence on the bearing capacity, the ductility and energy dissipation capacity of CFRP prestressed prisms reinforced concrete beams.

Key Words
CFRP; prism; cyclic; beam; ductility

Address
Jiongfeng Liang:
1) Jiangxi Engineering Research Center of Process and Equipment for New Energy, East China Institute of Technology, Nanchang, P.R.China
2) Faculty of Civil&Architecture Engineering, East China Institute of Technology, Nanchang, P.R.China
Yu Deng: College of Civil and Architecture Engineering, Guangxi University of Science and Technology, Liuzhou ,P.R.China
Minghua Hu and Dilian Tang: Faculty of Civil&Architecture Engineering, East China Institute of Technology, Nanchang, P.R.China

Abstract
During the last two decades, CFRP have been extensively used for repair and rehabilitation of existing structures as well as in new construction applications. For rehabilitation purposes CFRP are currently used to increase the load and the energy absorption capacities and also the shear strength of concrete columns. Thus, the effect of CFRP confinement on the strength and deformation capacity of concrete columns has been extensively studied. However, the majority of such studies consider empirical relationships based on correlation analysis due to the fact that until today there is no general law describing such a hugely complex phenomenon. Moreover, these studies have been focused on the performance of circular cross section columns and the data available for square or rectangular cross sections are still scarce. Therefore, the existing relationships may not be sufficiently accurate to provide satisfactory results. That is why intelligent models with the ability to learn from examples can and must be tested, trying to evaluate their accuracy for composite compressive strength prediction. In this study the forecasting of wrapped CFRP confined concrete strength was carried out using different Data Mining techniques to predict CFRP confined concrete compressive strength taking into account the specimens\' cross section: circular or rectangular. Based on the results obtained, CFRP confined concrete compressive strength can be accurately predicted for circular cross sections using SVM with five and six input parameters without spending too much time. The results for rectangular sections were not as good as those obtained for circular sections. It seems that the prediction can only be obtained with reasonable accuracy for certain values of the lateral confinement coefficient due to less efficiency of lateral confinement for rectangular cross sections.

Key Words
CFRP confined concrete; data mining; artificial neural networks; support vector machines

Address
Aires Camões: CTAC, Department of Civil Engineering, University of Minho, Guimarães, Portugal
Francisco F. Martins: ISISE, Department of Civil Engineering, University of Minho, Guimarães, Portugal

Abstract
Epoxy-coated reinforcing bars are widely used to protect the corrosion of the reinforcing bars in the RC elements under their in-service environments and external loads. In most field surveys, it was reported that the corrosion resistance of the epoxy-coated reinforcing bars is typically better than the uncoated bars. However, from the experimental tests conducted in the labs, it was reported that, under the same loads, the RC elements with epoxy-coated reinforcing bars had wider cracks than the elements reinforced with the ordinary bars. Although this conclusion may be true considering the bond reduction of the reinforcing bar due to the epoxy coating, the maximum service loads used in the experimental research may be a main reason. To answer these two phenomena, service performance of 15 RC beam specimens with uncoated and epoxy-coated reinforcements under different fatigue loads was experimentally studied. Influences of different coating thicknesses of the reinforcing bars, the fatigue load range and load upper limit as well as fatigue load cycles on the mechanical performance of RC test specimens are discussed. It is concluded that, for the test specimens subjected to the comparatively lower load range and load upper limit, adverse effect on the service performance of test specimens with thicker epoxy-coated reinforcing bars is negligible. With the increments of the coating thickness and the in-service loading level, i.e., fatigue load range, load upper limit and fatigue cycles, the adverse factor resulting from the thicker coating becomes noticeable.

Key Words
epoxy-coat bar; fatigue load; load upper limit; coating thickness; fatigue cycles

Address
Xiao-Hui Wang:
1) School of Energy, Geoscience, Infrastructure and Society, Heriot-Watt University, Edinburgh EH14 4AS, UK
2) Dept. of Civil Engineering, Shanghai Jiao Tong Univ., No. 800 Dongchuan Rd., Shanghai 200240, P.R. China
Yang Gao: Shanghai Municipal Engineering Design Institute (Group) Co., LTD, Shanghai 200092, P.R. China
Run-Dong Gao: Shanghai Key Laboratory of Engineering Structure Safety, Shanghai, 200032, P.R. China
ing Wang and Xi-La Liu: Dept. of Civil Engineering, Shanghai Jiao Tong Univ., No. 800 Dongchuan Rd., Shanghai 200240, P.R. China

Abstract
The aim of this study is to investigate the pH threshold value for the corrosion of steel reinforcement in concrete. A method was designed to attain the pH value of the pore solution on the location of the steel in concrete. Then the pH values of the pore solution on the location of steel in concrete were changed by exposing the samples to the environment (CO2 5%, RH 40%) to accelerate carbonation with different periods. Based on this, the pH threshold value for the corrosion of steel reinforcement had been examined by the methods of half-cell potential and electrochemical impedance spectra (EIS). The results have indicated that the pH threshold value for the initial corrosion of steel reinforcement in concrete was 11.21. However, in the carbonated concrete, agreement among whether steel corrosion was initiatory determined by the detection methods mentioned above could be found.

Key Words
carbonation, corrosion, steel reinforcement, pH threshold

Address
Qi Pu:
1) Suzhou Concrete and Cement Products Research Institute Co.,Ltd, Suzhou, 215000, China
2) China Building Materials Academy, Beijing 100024, China
Yan Yao and Ling Wang: China Building Materials Academy, Beijing 100024, China
Xingxiang Shi, Jingjing Luo and Yifei Xie: Suzhou Concrete and Cement Products Research Institute Co.,Ltd, Suzhou, 215000, China

Abstract
In this paper, a finite element model (FEM) in ATENA-3D software was constructed to investigate the behavior of circular ultra high performance concrete (UHPC) filled steel tube stub columns (UHPC-FSTCs) under concentric loading on concrete core. The CC3DNonLinCementitious2User material type for concrete in ATENA-3D software with some modifications of material laws, was adopted to model for UHPC core with consideration the confinement effect. The experimental results obtained from Schneider (2006) were then employed to verify the accuracy of FEM. Extensive parametric analysis was also conducted to examine the influence of concrete compressive strength, steel tube thickness and steel yield strength on the compressive behavior of short circular UHPC-FSTCs. It can be observed that the columns with thicker steel tube show better strength and ductility, the sudden drop of load after initial peak load can be prevented. Based on the regression analysis of the results from parametric study, simplified formulae for predicting ultimate loads and strains were proposed and verified by comparing with previous analytical models, design codes and experimental results.

Key Words
UHPC; ATENA-3D; finite element model; confinement effect; concrete filled steel tube

Address
An Le Hoang and Ekkehard Fehling: Faculty of Civil and Environmental Engineering, Institute of Structural Engineering, University of Kassel Kurt-Wolters-Stra

Abstract
The aim of this study is to build Machine Learning models to evaluate the effect of blast furnace slag (BFS) and waste tire rubber powder (WTRP) on the compressive strength of cement mortars. In order to develop these models, 12 different mixes with 288 specimens of the 2, 7, 28, and 90 days compressive strength experimental results of cement mortars containing BFS, WTRP and BFS+WTRP were used in training and testing by Random Forest, Ada Boost, SVM and Bayes classifier machine learning models, which implement standard cement tests. The machine learning models were trained with 288 data that acquired from experimental results. The models had four input parameters that cover the amount of Portland cement, BFS, WTRP and sample ages. Furthermore, it had one output parameter which is compressive strength of cement mortars. Experimental observations from compressive strength tests were compared with predictions of machine learning methods. In order to do predictive experimentation, we exploit R programming language and corresponding packages. During experimentation on the dataset, Random Forest, Ada Boost and SVM models have produced notable good outputs with higher coefficients of determination of R2, RMS and MAPE. Among the machine learning algorithms, Ada Boost presented the best R2, RMS and MAPE values, which are 0.9831, 5.2425 and 0.1105, respectively. As a result, in the model, the testing results indicated that experimental data can be estimated to a notable close extent by the model.

Key Words
blast furnace slag; waste tire rubber powder; compressive strength; Random Forest; Ada Boost; SVM; Bayes classifier models

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, Osmangazi University, Eskisehir, Turkey

Abstract
A large number of residential buildings in regions subjected to severe earthquakes do not have enough load carrying capacity. The most of them have been constructed without receiving any structural engineering attention. It is practically almost impossible to perform detailed experimental evaluation and analytical analysis for each building to determine their seismic vulnerability, because of time and cost constraints. This fact points to a need for a simple evaluation method that focuses on selection of buildings which do not have the life safety performance level by adopting the main requirements given in the seismic codes. This paper deals with seismic assessment of existing reinforced concrete residential buildings and contains an alternative simplified procedure for seismic evaluation of buildings. Accuracy of the proposed procedure is examined by taking account into existing 250 buildings. When the results of the proposed procedure are compared with those of the detailed analyses, it can be seen that the results are quite compatible. It is seen that the accuracy of the proposed procedure is about 80% according to the detailed analysis results of existing buildings. This accuracy percentage indicates that the proposed procedure in this paper can be easily applied to existing buildings to predict their seismic performance level as a first approach before implementing the detailed and complex analyses.

Key Words
buildings; confined concrete; earthquake engineering; reinforced concrete buildings; seismic evaluation of existing buildings

Address
Hamide Tekeli, Hakan Dilmac and Fuat Demir: Suleyman Demirel University, Department of Civil Engineering, Isparta, Turkey
Mustafa Gencoglu and Kadir Guler: Istanbul Technical University, Department of Civil Engineering, Istanbul, Turkey

Abstract
Maximum deflection in a beam is a serviceability design criterion and occurs generally at or close to the mid-span. This paper presents a methodology using neural networks for rapid prediction of mid-span deflections in reinforced concrete beams subjected to service load. The closed form expressions are further obtained from the trained neural networks. The closed form expressions take into account cracking in concrete at in-span and at near the interior supports and tension stiffening effect. The expressions predict the inelastic deflections (incorporating the concrete cracking) from the elastic moments and the elastic deflections (neglecting the concrete cracking). Five separate neural networks are trained since these have been postulated to represent all beams having any number of spans. The training, validating, and testing data sets for the neural networks are generated using an analytical-numerical procedure of analysis. The proposed expressions have been verified by comparison with the experimental results reported elsewhere and also by comparison with the finite element method (FEM). The proposed expressions, at minimal input data and minimal computation effort, yield results that are close to FEM results. The expressions can be used in every day design since the errors are found to be small.

Key Words
closed form expression; cracking; deflection; neural network; reinforced concrete; service load

Address
K. A. Patel: Civil Engineering Department, Indian Institute of Technology Delhi, New Delhi 110016, India
Sandeep Chaudhary and A. K. Nagpal: Civil Engineering Department, Malaviya National Institute of Technology Jaipur, Jaipur 302017, India

Abstract
A robust finite element based reinforced concrete bridge deck corrosion initiation model is applied for time-dependent probabilistic sensitivity analysis. The model is focused on uncertainties in the governing parameters that include variation of high performance concrete (HPC) diffusion coefficients, concrete cover depth, surface chloride concentration, holidays in reinforcements, coatings and critical chloride threshold level in several steel reinforcements. The corrosion initiation risk is expressed in the form of probability over intended life span of the bridge deck. Conducted study shows the time-dependent sensitivity analysis to evaluate the significance of governing parameters on chloride ingress rate, various steel reinforcement protection and the corrosion initiation likelihood. Results from this probabilistic analysis provide better insight into the effect of input parameters variation on the estimate of the corrosion initiation risk for the design of concrete structures in harsh chloride environments.

Key Words
corrosion initiation; probabilistic model; sensitivity analysis; SBRA; Monte-Carlo simulation; durability; performance assessment

Address
Pratanu Ghosh: Department of Civil and Environmental Engineering, California State University, Fullerton, CA-92834, Fullerton, California, USA
Petr Konečný and Petr Lehner: Department of Structural Mechanics, VŠB-Technical University of Ostrava, 708 33 Ostrava - Poruba, Czech Republic
Paul J. Tikalsky: Dean, College of Engineering, Architecture, and Technology, Oklahoma State University, 201 ATRC, Stillwater, OK 74078, USA

Abstract
Within the context of continuum mechanics, inelastic behaviours of constitutive responses are usually modelled by using phenomenological approaches. Elasto-plastic damage modelling is extensively used for concrete material in the case of progressive strength and stiffness deterioration. In this paper, a review of the main features of elasto-plastic damage modelling is presented for uniaxial stress-strain relationship. It has been reported in literature that the influence of Alkali-Silica Reaction (ASR) can lead to severe degradations in the modulus of elasticity and compression strength of the concrete material. In order to incorporate the effects of ASR related degradation, in this paper the constitutive model of concrete is based on the coupled damage-plasticity approach where degradation in concrete properties can be captured by adjusting the yield and damage criteria as well as the hardening moduli related parameters within the model. These parameters are adjusted according to results of concrete behaviour from the literature. The effect of ASR on the dynamic behaviour of a beam and a column are illustrated under moving load and cyclic load cases.

Key Words
alkali-slica reaction; coupled damage-plasticity; dynamic behaviour

Address
R. Emre Erkmen, Nadarajah Gowripalan and Vute Sirivivatnanon: School of Civil and Environmental Engineering, University of Technology Sydney, NSW 2007, Australia

Abstract
In this study, vibration and stability of concrete pipes reinforced with carbon nanotubes (CNTs) conveying fluid are presented. Due to the existence of CNTs, the structure is subjected to magnetic field. The radial fore induced with fluid is calculated using Navier-Stokes equations. Characteristics of the equivalent composite are determined using Mori-Tanaka model. The concrete pipe is simulated with classical cylindrical shell model. Employing energy method and Hamilton\'s principal, the motion equations are derived. Frequency and critical fluid velocity of structure are obtained analytically based on Navier method for simply supported boundary conditions at both ends of the pipe. The effects of fluid, volume percent of CNTs, magnetic field and geometrical parameters are shown on the frequency and critical fluid velocity of system. Results show that with increasing volume percent of CNTs, the frequency and critical fluid velocity of concrete pipe are increased.

Key Words
concrete pipe; fluid; modeling; critical fluid velocity; vibration

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

Abstract
In this paper, nonlinear vibration of embedded nanocomposite concrete is investigated based on Timoshenko beam model. The beam is reinforced by with agglomerated silicon dioxide (SiO2) nanoparticles. Mori-Tanaka model is used for considering agglomeration effects and calculating the equivalent characteristics of the structure. The surrounding foundation is simulated with Pasternak medium. Energy method and Hamilton\'s principal are used for deriving the motion equations. Differential quadrature method (DQM) is applied in order to obtain the frequency of structure. The effects of different parameters such as volume percent of SiO2 nanoparticles, nanoparticles agglomeration, elastic medium, boundary conditions and geometrical parameters of beam are shown on the frequency of system. Numerical results indicate that with increasing the SiO2 nanoparticles, the frequency of structure increases. In addition, considering agglomeration effects leads to decrease in frequency of system.

Key Words
vibration of concrete beam; agglomerated SiO2 nanoparticles; Pasternak medium; DQM; Mori-Tanaka model

Address
Maryam Shokravi: Buein Zahra Technical University, Buein Zahra, Qazvin, Iran


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