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CONTENTS
Volume 8, Number 5, October 2011
 

Abstract
Before deciding if structures exposed to high temperature are to be repaired or demolished, their final state should be carefully examined. Destructive and non-destructive testing methods are generally applied for this purpose. Compressive strength and color change in mortars are observed as a result of the effects of high temperature. In this study, ordinary and pozzolan-added mortar samples were produced using different aggregates, and exposed to 100, 200, 300, 600, 900 and 1200

Key Words
color; concrete; high temperature; neural network; pulse velocity; strength.

Address
N. Yuzer: Yildiz Technical University, Department of Civil Engineering, Istanbul 34210, Turkey
B. Akbas: Gebze Institute of Technology, Kocaeli, Turkey
A.B. Kizilkanat: Yildiz Technical University, Department of Civil Engineering, Istanbul 34210, Turkey


Abstract
Although concrete is believed to be a durable material, concrete structures have been degraded by severe environmental conditions such as the effects of chloride and chemical, abrasion, and other deterioration processes. Therefore, durability evaluation has been required to ensure the long term serviceability of structures located in chloride exposed environments. Recently, probability-based durability analysis and design have proven to be reliable for the service-life predictions of concrete structures. This approach has been successfully applied to durability estimation and design of concrete structures. However, currently it is difficult to find an appropriate method engineers can use to solve these probability-based diffusion problems. In this paper, computer software has been developed to facilitate probability-based durability analysis and design. This software predict the chloride diffusion using the Monte Carlo simulation method based on Fick

Key Words
durability; corrosion; chloride penetration; service life; concrete structure.

Address
Kyung-Joon Shin: Department of Civil Engineering, Chungnam National University, Daejeon, Korea
Jee-Sang Kim: Department of Civil Engineering, Seokyeong University, Seoul, Korea
Kwang-Myong Lee: Department of Civil and Environmental Engineering, Sungkyunkwan University, Suwon, Korea

Abstract
This paper describes the development of a fiber reinforced concrete (FRC) unit cell for analyzing concrete structures by executing a multiscale analysis procedure using the theory of homogenization. This was achieved through solving a periodic unit cell problem of the material in order to evaluate its macroscopic properties. Our research describes the creation of an FRC unit cell through the use of concrete paste generic information e.g. the percentage of aggregates, their distribution, and the percentage of fibers in the concrete. The algorithm presented manipulates the percentage and distribution of these aggregates along with fiber weight to create a finite element unit cell model of the FRC which can be used in a multiscale analysis of concrete structures.

Key Words
FRC-fibered reinforced concrete; multiscale analysis; concrete unit cell; elastic properties; mesoscale concrete finite element model.

Address
Erez Gal and Roman Kryvoruk: Department of Structural Engineering, Ben-Gurion University, Beer-Sheva, Israel

Abstract
The Finite Element Method (FEM) was employed to demonstrate that accurate simulations of seismically repaired and retrofitted reinforced concrete shear walls can be achieved provided a good analysis program with comprehensive models for material and structural behaviour is used. Furthermore, the analysis tool should have the capability to retain residual damage experienced by the original structure and carry it forward in the repaired and retrofitted structure. The focus herein is to provide quick, simple, but reliable modelling procedures for repair and retrofitting strategies such as concrete replacement, addition of diagonal reinforcing bars, bolting of external steel plates, and bonding of external steel plates and fibre reinforced polymer sheets, thus illustrating versatility in the modelling. Slender, squat, and slender-squat shear walls were investigated. The modelling utilized simple rectangular membrane elements for the concrete, truss bar elements for the steel and FRP retrofitting materials, and bond-link elements for the bonding interface between steel or FRP to concrete. The analyses satisfactorily simulated seismic behaviour, including lateral load capacity, displacement capacity, energy dissipation, hysteretic response, and failure mode.

Key Words
finite element modelling; reinforced concrete shear walls; seismic repair; seismic retrofitting; nonlinear finite element analysis.

Address
W. Leonardo Cortes-Puentes and Dan Palermo: Department of Civil Engineering, University of Ottawa, 161 Louis Pasteur,
Ottawa, ON, Canada, K1N 6N5

Abstract
The signal-based acoustic emission (AE) characterization of concrete fracture process utilizing home-programmed AE monitoring system was performed for three kinds of static loading tests (Cubic-splitting, Direct-shear and Pull-out). Each test was carried out to induce a distinct fracture mode of concrete. Apart from monitoring and recording the corresponding fracture process of concrete, various methods were utilized to distinguish the characteristics of detected AE waveform to interpret the information of fracture behavior of AE sources (i.e. micro-cracks of concrete). Further, more signal-based characters of AE in different stages were analyzed and compared in this study. This research focused on the relationship between AE signal characteristics and fracture processes of concrete. Thereafter, the mode of concrete fracture could be represented in terms of AE signal characteristics. By using cement-based piezoelectric composite sensors, the AE signals could be detected and collected with better sensitivity and minimized waveform distortion, which made the characterization of AE during concrete fracture process feasible. The continuous wavelet analysis technique was employed to analyze the wave-front of AE and figure out the frequency region of the P-wave & S-wave. Defined RA (rising amplitude), AF (average frequency) and P-wave & S-wave importance index were also introduced to study the characters of AE from concrete fracture. It was found that the characters of AE signals detected during monitoring could be used as an indication of the cracking behavior of concrete.

Key Words
concrete; fracture; acoustic emission; cement-based piezoelectric composite; wave.

Address
Youyuan Lu and Zongjin Li: Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
Lei Qin: Department of Civil Engineering, University of Jinan, Jinan, Shandong Province, China

Abstract
This paper studied the cement efficiency factor (k factor) of high calcium Class F fly ash. This k factor represents a unit of fly ash with efficiency equivalent to k unit of cement. The high calcium Class F fly ash was used to replace cement in concrete. The modified Bolomey

Key Words
efficiency factor; fly ash; Class F; concrete; multi-linear regression analysis.

Address
V. Sata, P. Khammathit and P. Chindaprasirt: Sustainable Infrastructure Research and Development Center,
Department of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand

Abstract
With respect to rehabilitation, strengthening and retrofitting of existing and deteriorated columns in buildings and bridges, CFRP sheets have been found effective in enhancing the performance of existing RC columns by wrapping and bonding CFRP sheets externally around the concrete. Concrete columns and piers that are confined by both lateral steel reinforcement and CFRP are sometimes referred to as

Key Words
confined concrete; column; compressive strength; carbon fiber; neural network; retrofit.

Address
Andres W.C. Oreta and Jason M.C. Ongpeng: De La Salle University 2401 Taft Ave., Manila, Philippines


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