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CONTENTS
Volume 5, Number 6, December 2008
 

Abstract
Containment structures not only are leak-tight barriers, but also may be subjected to impacts caused by tornado-generated projectiles, aircraft crashes or the fragments of missile warhead. This paper presents the results of an experimental study of the impact resistance of steel fiber-reinforced concrete against 45 g projectiles at velocity around 2500 m/s. An explosively formed projectile (EFP) was designed to generate an equivalent missile fragment. The formation and velocity of EFP are measured by flash x-ray. A switch made of double-layered thin copper sheets controlled the exposure time of each flash x-ray. The influence of the fiber volume fraction on the crater diameter of concrete slab and the residual velocity of the projectile were studied. The residual velocity of the projectile decreased as the fiber volume fractions increased. In this work, the residual velocity of the projectile was to 44% that of plain concrete when the fiber volume fraction exceeded 1.5%. Based on the present finding, steel fiber reinforced concrete with the fiber volume fraction exceeding 1.5% appear to be more efficient in protection against high velocity fragment impact.

Key Words
steel fiber-reinforced concrete; high velocity impact; EFP.

Address
Tso-Liang Teng; Department of Mechanical Engineering, Da-Yeh University, 112. Shan-Jiau Rd. Da-Tsuen, Changhua 515, Taiwan, R.O.C
Yi-An Chu and Bor-Cherng Shen; Chung-Shan Institute of Science and Technology, P. O. Box 90008-17-10 Lung-Tan, Tao-Yuan 325, Taiwan, R.O.C.

Abstract
In this research, the self-centering effect in precast and prestressed reinforced concrete structures was investigated experimentally. The reinforced concrete beams and columns were precast and connected by post-tensioning tendons passing through the center of the beams as well as the panel zone of the connections. Three beam-to-interior-column connections were constructed to investigate parameters such as beam to column interfaces (steel on steel or plastic on plastic), energy dissipating devices (unbonded buckling restrained steel bars or steel angles) and the spacing of hoops in the panel zone. In addition to the self-centering effect, the shear strength in the panel zone of interior column connections was experimentally and theoretically evaluated, since the panel zone designed by current code provisions may not be conservative enough to resist the panel shear increased by the post-tensioning force.

Key Words
beam-column connections; precast; prestressed concrete; self-centering; shear distortion, large-scale testing.

Address
Chin-Tung Cheng; Department of Construction Engineering, National Kaohsiung First University of Science & Technology, 1 University Road, Yenchao, Kaohsiung 824, Taiwan.

Abstract
The corrosion of RC structures demonstrates very complicated forms of deterioration intermingled together but all pointing to a decrease in the durability of RC structures due to the corrosion of reinforcing bars. Until now, nondestructive techniques, such as half-cell potential and polarization resistance, have been widely available in the world. The former provides information on the probability of corrosion while the latter is associated with information concerning corrosion rates. Inversion by the boundary element method (IBEM) was developed for considering concrete resistivity. The applicability of the procedure was examined through a numerical analysis and electrolytic tests for RC slabs. A distribution in such concrete resistivity is relatively inhomogeneous including cracks on the surface of slabs. Regarding cracks in concrete, the relative coefficient of concrete resistance was introduced to perform its analysis. Further, the procedure will be developed to identify the corroded region visually using 3-D VRML.

Key Words
half-cell potential; BEM; concrete resistivity; corrosion; corrosion area; VRML.

Address
Je-Woon Kyung; Construction Division 1, Korea Institute of Construction & Transportation Technology Evaluation and Planning (KICTEP), 1600 Kwangyang-dong, Dongan-gu, Anayng-si, Gyeonggi-do, 431-060, Korea
Sung-Ho Tae and Han-Seung Lee; School of Architecture & Architectural Engineering, Hanyang University 1271, Sa-1dong, SangNokgu, Ansan, Gyunggido, 425-791, Korea
Sung-Bok Lee; Housing and Urban Research Institute, Korea National Housing Corporation 175 Gumi-dong, Seongnam-si, Gyeonggi-do, 463-704 Korea

Abstract
The effects of fly ash and superplasticizer (SP) on workability of concrete are quite difficult to predict because they are dependent on other concrete ingredients. Because of high complexity of the relations between workability and concrete compositions, conventional regression analysis could be not sufficient to build an accurate model. In this study, a workability model has been built using artificial neural networks (ANN). In this model, the workability is a function of the content of all concrete ingredients, including cement, fly ash, blast furnace slag, water, superplasticizer, coarse aggregate, and fine aggregate. The effects of water/binder ratio (w/b), fly ash-binder ratio (fa/b), superplasticizer-binder ratio (SP/b), and water content on slump were explored by the trained ANN. This study led to the following conclusions: (1) ANN can build a more accurate workability model than polynomial regression. (2) Although the water content and SP/b were kept constant, a change in w/b and fa/b had a distinct effect on the workability properties. (3) An increasing content of fly ash decreased the workability, while raised the slump upper limit that can be obtained.

Key Words
fly ash; superplasticizer; workability; artificial neural networks.

Address
I-Cheng Yeh; Department of Information Management, Chung-Hua Univ. Hsin Chu, Taiwan 30067, R.O.C.

Abstract
Among artificial intelligence-based computational techniques, adaptive neuro-fuzzy inference systems (ANFIS) are particularly suitable for modelling complex systems with known input-output data sets. Such systems can be efficient in modelling non-linear, complex and ambiguous behaviour of cement-based materials undergoing single, dual or multiple damage factors of different forms (chemical, physical and structural). Due to the well-known complexity of sulfate attack on cement-based materials, the current work investigates the use of ANFIS to model the behaviour of a wide range of self-consolidating concrete (SCC) mixture designs under various high-concentration sodium sulfate exposure regimes including full immersion, wetting-drying, partial immersion, freezing-thawing, and cyclic cold-hot conditions with or without sustained flexural loading. Three ANFIS models have been developed to predict the expansion, reduction in elastic dynamic modulus, and starting time of failure of the tested SCC specimens under the various high-concentration sodium sulfate exposure regimes. A fuzzy inference system was also developed to predict the level of aggression of environmental conditions associated with very severe sodium sulfate attack based on temperature, relative humidity and degree of wetting-drying. The results show that predictions of the ANFIS and fuzzy inference systems were rational and accurate, with errors not exceeding 5%. Sensitivity analyses showed that the trends of results given by the models had good agreement with actual experimental results and with thermal, mineralogical and micro-analytical studies.

Key Words
Neuro-fuzzy systems; self-consolidating concrete; sulfate attack; environmental conditions; flexural loading.

Address
M. T. Bassuoni; School of Planning, Architecture and Civil Engg. Centre for Built Environment Research, Queen\'s University of Belfast, Belfast BT9 5AG, UK
M. L. Nehdi; Department of Civil and Environmental Engineering, The Univ. of Western Ontario London, Ontario N6A 5B9, Canada


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