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CONTENTS
Volume 1, Number 3, October 2013
 

Abstract
While recognizing the problem of reinforcement corrosion and premature structural deterioration of reinforced concrete (RC) structures as a combined effect of mechanical and environmental actions (carbonation, ingress of chlorides), emphasis is given on the effect of the latter, as most severe and unpredictable action. In this study, a simulation tool, based on proven predictive models utilizing principles of chemical and material engineering, for the estimation of concrete service life is applied on an existing reinforced concrete bridge (resund Link) located in a chloride environment. After a brief introduction to the structure of the models used, emphasis is given on the physicochemical processes in concrete leading to chloride induced corrosion of the embedded reinforcement. By taking under consideration the concrete, structural and environmental properties of the bridge investigated, an accurate prediction of its service life is taking place. It was observed that the proposed, and already used, relationship of service lifetime- cover is almost identical with a mean line between the lines derived from the minimum and maximum critical values considered for corrosion initiation. Thus, an excellent agreement with the project specifications is observed despite the different ways used to approach the problem. Furthermore, different scenarios of concrete cover failure, in the case when a coating is utilized, and extreme deicing salts attack are also investigated.

Key Words
bridge; chloride attack; concrete; durability; failure scenarios; protective measures; service life

Address
Vagelis G. Papadakis: Department of Environmental and Natural Resources Management, University of Patras, Seferi 2, GR-30100, Agrinio, Greece

Abstract
The results of experimental testing of the effect of confined concrete on compressive strength and ductility of concrete beam subjected to pure bending are presented. The effect of different stirrups forms and spacing, as well as different concrete strengths, on beam carrying capacity and ductility were analyzed. Ultimate strength capacity and deflection of concrete beam increase with the decrease in stirrups spacing. Stirrup form has a great effect on the ultimate carrying capacity and ductility of concrete beam. Stirrups which confined the region of concrete in the compression more contribute to greater compression strength of concrete than common stirrups at the perimeter of the entire cross-section of the beam.

Key Words
experiment; confined concrete; beam; compressive strength; stirrups effect

Address
Jure Radnić, Radoslav Markić, Alen Harapin and Domagoj Matešan: Faculty of Civil Engineering, Architecture and Geodesy, University of Split, 21000 Split, Croatia

Abstract
Modal testing, widely accepted and applied method for determining the dynamic characteristics of structures for operational conditions, uses known or unknown vibrations in structures. The method\'s common applications includes estimation of dynamic characteristics and also damage detection and monitoring of structural performance. In this study, the structural identification of concrete arch dams is determined using ambient vibration tests which is one of the modal testing methods. For the purpose, several ambient vibration tests are conducted to an arch dam. Sensitive accelerometers were placed on the different points of the crest and a gallery of the dam, and signals are collected for the process. Enhanced Frequency Domain Decomposition technique is used for the extraction of natural frequencies, mode shapes and damping ratios. A total of eight natural frequencies are attained by experimentally for each test setup, which ranges between 0-12 Hz. The results obtained from each ambient vibration tests are presented and compared with each other in detail. There is a good agreement between the results for all measurements. However, the theoretical fundamental frequency of Berke Arch Dam is a little different from the experimental.

Key Words
arch dams; ambient vibration test; dynamic characteristics; signal processing

Address
Bans Sevim: Yildiz Technical University, Department of Civil Engineering, 34220, Istanbul, Turkey
Ahmet Can Altunisik and Alemdar Bayraktar: Yildiz Technical University, Department of Civil Engineering, 61080, Trabzon, Turkey

Abstract
Mortar microstructure is considered as a three-phase composite material, which is cement paste, fine aggregate and interfacial transition zone. Interfacial transition zone is the weakest link between the cement paste and fine aggregate, so it has a significant role to determine the properties of cementitious composites. In this study, specimens (w/c = 0.35, 0.45, 0.55) with various volume fractions of fine aggregate ( f V = 0, 0.1, 0.2, 0.3 and 0.4) were cast and tested. To predict the equivalent migration coefficient ( e M ) and migration coefficient of interfacial transition zone ( itz M ), double-inclusion method and Mori-Tanaka theory were used to estimate. There are two stages to estimate and calculate the thickness of interfacial transition zone ( h ) and migration coefficient of interfacial transition zone ( itz M ). The first stage, the data of experimental chloride ion migration coefficient ( s M ) was used to calculate the equivalent migration coefficient of fine aggregate with interfacial transition zone ( e M ) by Mori-Tanaka theory. The second stage, the thickness of interfacial transition zone ( h ) and migration coefficient of interfacial transition zone ( itz M ) was calculated by Hori and Nemat-Nasse\'s double inclusion model. Between the theoretical and experimental data a comparison was conducted to investigate the behavior of interfacial transition zone in mortar and the effect of interfacial transition zone on the chloride migration coefficient, the results indicated that the numerical simulations is derived to the itz m M M ratio is 2.11~8.28. Additionally, thickness of interfacial transition zone is predicted from 10m, 60 to 80m, 70 to 100mand 90 to 130mfor SM30, M35, M45 and M55, respectively.

Key Words
interfacial transition zone; double-inclusion method; Mori-Tanaka theory; migration coefficient of mortar

Address
S.H. Weng: nstitute of Materials Engineering, National Taiwan Ocean University
C.C. Yang: Pei-Ning Road, Keelung, Taiwan, 20224, ROC

Abstract
The use of steel bracing systems is a popular method for the strengthening of existing reinforced concrete (RC) frames and may lead to a substantial increase of both strength and stiffness. However, in most retrofitting cases, the main target is the increase of the energy dissipation capacity. This paper studies numerically the efficiency of a specific strengthening methodology which utilizes a steel link element having a cross-section of various shapes, connected to the RC frame through bracing elements. The energy is dissipated through the yielding of the steel link element. The case studied is a typical one bay, single-storey RC frame, constructed according to older code provisions, which is strengthened through two different types of link elements. The presented numerical models are based on tests which are simulated in order to gain a better insight of the behaviour of the strengthened structures, but also in order to study the effects of different configurations for the link element. The behaviour of the strengthened frames is studied with respect to the one of the original bare frame. Moreover, the numerically obtained results are compared to the experimentally obtained ones, in order to verify the effectiveness of the applied simulation methodology.

Key Words
strengthening; non-linear analysis; concrete structures; earthquake engineering; finite elements method

Address
Kyriaki Georgiadi-Stefanidi and Euripidis Mistakidis: Laboratorty of Structural Analysis and Design, Department of Civil Engineering, University of Thessaly, Pedion Areos, GR-38334 Volos, Greece
Kosmas Athanasios Stylianidis: Laboratory of Reinforced Concrete and Masonry Structures, Department of Civil Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece


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