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CONTENTS
Volume 6, Number 4, August 2009
 

Abstract
In this paper an experimental study of the influence of hot springs curing upon concrete properties was carried out. The primary variables of the investigation include water-to-binder ratio (W/B), pozzolanic material content and curing condition. Three types of hot springs, in the range 40-90oC, derived from different regions in Taiwan were adopted for laboratory testing of concrete curing. In addition, to compare with the laboratory results, compressive strength and durability of practical concrete were conducted in a tunnel construction site. The experimental results indicate that when concrete comprising pozzolanic materials was cured by a hot spring with high temperature, its compressive strength increased rapidly in the early ages due to high temperature and chloride ions. In the later ages, the trend of strength development decreased obviously and the strength was even lower than that of the standard cured one. The results of durability test show that concrete containing 30-40% Portland cement replacement by pozzolanic materials and with W/B lower than 0.5 was cured in a hot spring environment, then it had sufficient durability to prevent steel corrosion. Similar to the laboratory results, the cast-inplace concrete in a hot spring had a compressive strength growing rapidly at the earlier age and slowly at the later age. The results of electric resistance and permeability tests also show that concrete in a hot spring had higher durability than those cured in air. In addition, there was no neutralization reaction being observed after the 360-day neutralization test. This study demonstrates that the concrete with enough compressive strength and durability is suitable for the cast-in-place structure being used in hot spring areas.

Key Words
temperature; curing; compressive strength; durability.

Address
How-Ji Chen: Department of Civil Engineering, National Chung-Hsing University, No. 250, Kuo Kuang Road, Taichung, Taiwan, R.O.C.
Tsung-Yueh Yang: Department of Civil Engineering, National Chung-Hsing University, No. 250, Kuo Kuang Road, Taichung, Taiwan, R.O.C.
Chao-Wei Tang: Department of Civil Engineering & Engineering Informatics, Cheng-Shiu University, No. 840,
Chengcing Road, Niaosong Township, Kaohsiung County, Taiwan, R.O.C.

Abstract
The lack of safety of bridge deck structures causes frequent repair and strengthening of such structures. The repair induces great loss of economy, not only due to direct cost by repair, but also due to stopping the public use of such structures during repair. The major reason for this frequent repair is mainly due to the lack of realistic and accurate assessment system for the bridge decks. The purpose of the present research was to develop a realistic expert system, called Bridge Slab-Expert which can evaluate reasonably the condition as well as the service life of concrete bridge decks, based on the deterioration models that are derived from both the structural and environmental effects. The diagnosis assessment of deck slabs due to structural and environmental effects are developed based on the cracking in concrete, surface distress and structural distress. Fuzzy logic is utilized to handle uncertainties and imprecision involved. Finally, Bridge Slab-Expert is developed for prediction of safety and remaining service life based on the chloride ions penetration and fick

Key Words
reliability and safety; computer; concrete; durability; service life; environment condition; software.

Address
Ali Akbar Ramezanianpour: Department of Civil and Environment Engineering, Amirkabir University of Technology, Tehran, Iran
Vahid Shahhosseini: Construction Engineering and Management, Amirkabir University of Technology, Tehran, Iran
Faramarz Moodi: Concrete Technology & Durability Research Center, Amirkabir University of Technology, Tehran, Iran

Abstract
Fiber Reinforced Polymer (FRP) is widely used for retrofitting concrete structures for various purposes. Especially, for the retrofitting of concrete structures subjected to blast loads, FRP is proven to be a very effective retrofitting material. However, a systematic design procedure to implement FRP for concrete structure retrofitting against blast loads does not exist currently. In addition, in case of concrete structures with inarticulate geometrical boundary conditions such as arch structures, an effective analysis technique is needed to obtain reliable results based on minimal analytical assumptions. Therefore, in this study, a systematic and efficient blast analysis procedure for FRP retrofitting design of concrete arch structure is suggested. The procedure is composed of three sequential parts of preliminary analysis, breach and debris analysis, and retrofit-material analysis. Based on the suggested procedure, blast analyses are carried out by using explicit code, LS-DYNA. The study results are discussed in detail.

Key Words
blast analysis procedure; concrete arch structure; preliminary analysis; breach/debris analysis; retrofit material analysis; FRP retrofitting; blast retrofit design.

Address
Jin-Won Nam: Department of Civil and Environmental Engineering, University of California, Davis
One Shield Ave., Davis, CA 95616, U.S.A.
School of Civil and Environmental Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, South Korea
Ho-Jin Kim: Institute of Technology Research Planning Team, ATMACS Co., Ltd.513-22 Sangdaewon-dong, Jungwon-gu, Seongnam-si, Gyunggi-do 462-120, South Korea
Na-Hyun Yi: School of Civil and Environmental Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, South Korea
In-Soon Kim: School of Civil and Environmental Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, South Korea
Jang-Ho Jay Kim: School of Civil and Environmental Engineering, Yonsei University, 134 Shinchon-dong,
Seodaemun-gu, Seoul 120-749, South Korea
Hyung-Jin Choi: Karagozian & Case 2550 N, Hollywood Way Suite 500, Burbank, CA 91505, U.S.A.

Abstract
A new formulation based on lumped plasticity and inelastic hinges is presented in this paper for nonlinear analysis of Reinforced Concrete (RC) frame structures. Inelastic hinge behaviour is described using the principles of Continuum Damage Mechanics (CDM). Member formulation contains provisions to model stiffness degradation due to cracking of concrete and yielding of reinforcing steel. Depending on its nature, cracking is classified as concentrated or distributed. Concentrated cracking is accounted through a damage variable and its growth is defined based on strain energy principles. Presence of distributed flexural cracks in a member is taken care of by modelling it as non-prismatic. Plasticity theory supported by effective stress concept of CDM is applied to describe the post-yield response. Nonlinear quasi-static analysis is carried out on a RC column and a wide two-storey RC frame to verify the formulation. The column is subjected to constant axial load and monotonic lateral load while the frame is subjected to only lateral load. Computed results are compared with those due to experiments or other numerical methods to validate the performance of the formulation and also to highlight the contribution of distributed cracking on global response.

Key Words
reinforced concrete frame; plastic hinges; continuum damage mechanics; plasticity theory; nonlinear response.

Address
J. Rajasankar

Abstract
Experiments were designed to investigate the flow behavior of portland cement paste and concrete incorporating superplasticizers. The paste and concrete mixtures were subjected to prolonged mixing for up to 110 min at high temperature. The yield stress values of concrete and that of the corresponding cement paste were measured using a rotating rheometer and viscometer, respectively. The results reveal a weak linear correlation between the yield stress of concrete mixtures and that of the corresponding cement pastes. Results also indicate that the yield stress of concrete varies in a linear fashion with the elapsed time, while its variations with the temperature and superplasticizer dosage follow power and inverse power functions, respectively. In this study, the genetic algorithms (GA) technique was used to predict the yield stress of concrete considering various parameters, such as the mixing time, ambient temperature, and superplasticizer dosage. A sensitivity study was conducted to evaluate the ability of the GA equations thus developed to capture the effects of test parameters on the yield stress of concrete. It was found that the GA equations were sensitive to the effects of test parameters and provided yield stress predictions that compared well with corresponding experimental data.

Key Words
genetic algorithm; rheology; cement paste; concrete; high temperature; mixing time; superplasticizer; yield stress.

Address
S. Al Martini: Department of Civil and Environmental Engineering, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B9, Canada
M. Nehdi: Department of Civil and Environmental Engineering, The University of Western Ontario, 1151 Richmond Street, London, ON N6A 5B9, Canada


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