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CONTENTS
Volume 10, Number 3, September 2012
 

Abstract
Carbonation is a widespread degradation of concrete and may be coupled with more severe degradations. An experimental investigation was carried out to study the effect of carbonation on chloride ion diffusion of concrete. The characteristic of concrete after carbonation was measured, such as carbonation depth, strength and pore structure. Results indicated that carbonation depth has a good linear relation with square root of carbonate time, and carbonation can improve compressive strength, but lower flexural strength. Results about pore structure of concrete before and after carbonation have shown that carbonation could cause a redistribution of the pore sizes and increase the proportion of small pores. It also can decrease porosities, most probable pore size and average pore diameters. Chloride ion diffusion of concrete after carbonation was studied through natural diffusion method and steady state migration testing method respectively. It is supposed that the chloride ion concentration of carbonation region is higher than that of the sound region because of the separation of fixed salts, and chloride ion diffusion coefficient was increased due to carbonation action evidently.

Key Words
concrete; carbonation; pore structure; chloride ion diffusion.

Address
Shiping Zhang and Binghua Zhao: Department of Architecture Civil Engineering, Nanjing Institute of Technology, Nanjing 211167, P.R. China

Abstract
In this paper, the effect of finishing methods on the relationships between compressive strength, permeability and void ratio of porous concrete (POC) or pervious concrete is discussed, using core specimens taken from actually constructed POC pavement. To attain reliable performance in the construction work, a newly designed finisher for POC is developed, and the performances as well as methods for controlling void ratio are examined. The POC pavements were finished with three finishing methods viz., no finishing, finishing with standard compactor and finishing with prototype compactor. The results show that the prototype POC finisher is efficient in controlling the void ratio and the quality of POC pavements. The relationships between compressive strength as well as permeability and void ratio of the in-situ POC pavements finished by the prototype machine were obtained. They are slightly different from the laboratory test results owing mainly to the mold effect and the differences in compaction modes.

Key Words
porous concrete; compaction; compressive strength; void ratio; pavement; finishing method.

Address
Shigemitsu Hatanaka, Naoki Mishima, Takeshi Nakagawa and Hirotomo Morihana: Department of Architecture, Faculty of Engineering, Mie University, Mie 514-8507, Japan; Prinya Chindaprasirt: Sustainable Infrastructure Research and Development Center, Department of Civil Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, 40002 Thailand

Abstract
The need for long-span members increases gradually in recent years, which makes issues not only on ultimate strength but also on excessive deflection of horizontal members important. In building structures, the post-tension methods with unbonded tendons are often used for long-span members to solve deflection problems. Previous studies on prestressed flexural members with unbonded tendons, however, were mostly focused on the ultimate strength. For this reason, their approaches are either impossible or very difficult to be implemented for serviceability check such as deflection, tendons stress, etc. Therefore, this study proposed a flexural behavior model for post-tensioned members with unbonded tendons that can predict the initial behavior, before and after cracking, service load behavior and ultimate strength. The applicability and accuracy of the proposed model were also verified by comparing with various types of test results including internally and externally post-tensioned members, a wide range of reinforcement ratios and different loading patterns. The comparison showed that the proposed model very accurately estimated both the flexural behavior and strength for these members. Particularly, the proposed model well reflected the effect of various loading patterns, and also provided good estimation on the flexural behavior of excessively reinforced members that could often occur during reinforcing work.

Key Words
unbonded tendon; prestress; flexural behavior; post-tension; flexural strength.

Address
Kang Su Kim and Deuck Hang Lee: Department of Architectural Engineering, University of Seoul, Seoul, Korea

Abstract
A total of nine reinforced concrete corbels were tested, in this study. Six were externally strengthened with carbon fiber reinforced plastics (CFRP), in the horizontal direction. The cross-sectional area of CFRP and the shear span-to-effective depth ratios are the parameters considered, in this study. Test results indicate that the higher the cross-sectional area of CFRP, the higher is the shear strength of the corbels, and the lower the shear span-to-effective depth ratios, the higher is the shear strength of corbels. The shear strength predicted by the design provisions in section 11.8 of the ACI Code, the strutand- tie model in Appendix A of the ACI Code, and the softened strut-and-tie (SST) model were compared with the test results. The comparisons show that both the strut-and-tie model in Appendix A of the ACI Code, and the SST model can accurately predict the shear strength of reinforced concrete corbels, strengthened with CFRP.

Key Words
reinforced concrete corbel; shear strength; carbon fiber reinforced plastics (CFRP).

Address
Wen-Yao Lu: Department of Interior Design, China University of Technology, Taipei 11695, Taiwan, R.O.C.; Hsin-Wan Yu: Department of Civil Engineering and Hazard Mitigation Design, China University of Technology, Taipei 11695, Taiwan, R.O.C.; Chun-Liang Chen, Tzong-Hwan Yang and Yu-Sin Lin: Department of Interior Design, China University of Technology, Taipei 11695, Taiwan, R.O.C.

Abstract
The aim of the study is to determine the modal parameters of a prototype damaged arch dam by operational modal analysis (OMA) method for some damage scenarios. For this purpose, a prototype arch dam-reservoir-foundation model is constructed under laboratory conditions. Ambient vibration tests on the arch dam model are performed to identify the modal parameters such as natural frequency, mode shape and damping ratio. The tests are conducted for four test-case scenarios: an undamaged dam with empty reservoir, two different damaged dams with empty reservoirs, and a damaged dam with full reservoir. Loading simulating random impact effects is applied on the dam to crack. Cracks and fractures occurred at the middle of the upper part of the dams and distributed through the abutments. Sensitivity accelerometers are placed on the dams

Key Words
arch dam; ambient vibration test; damage scenario; enhanced frequency domain decomposition; stochastic subspace identification; modal parameter identification; operational modal analysis.

Address
Baris Sevim: Yildiz Technical University, Department of Civil Engineering, Istanbul, Turkey; Ahmet Can Altunisik and Alemdar Bayraktar: Karadeniz Technical University, Department of Civil Engineering, Trabzon, Turkey

Abstract
Optimum cost design of a simply supported reinforced concrete beam is presented in this paper. In the formulation of the optimum design problem, the height and width of the beam, and reinforcement steel area are treated as design variables. The design constraints are implemented according to ACI 318-08 and studies in the literature. The objective function is taken as the cost of unit length of the beam consisting the cost of concrete, steel and shuttering. The solution of the design problem is obtained using the artificial bee colony algorithm which is one of the recent additions to metaheuristic techniques. The artificial bee colony algorithm is imitated the foraging behaviors of bee swarms. In application of this algorithm to the constraint problem, Deb\'s constraint handling method is used. Obtained results showed that the optimum value of numerical example is nearly same with the existing values in the literature.

Key Words
optimization; metaheuristic; artificial bee colony algorithm; reinforced concrete beams.

Address
H.T. Ozturk, Ay. Durmus and Ah. Durmus: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Abstract
This work intends to contribute for the improvement of the procedure suggested by Brazilian Technical Code that takes into account the cracked concrete stiffness in the estimative of the displacement of reinforced concrete beams submitted to service loads. A damage constitutive model accounting for induced anisotropy, plastic deformations and bimodular elastic response is used in order to simulate the concrete behaviour, while an elastoplastic behaviour is admitted for the reinforcement. The constitutive models were implemented in a program for bars structures analysis with layered finite elements. Initially, the damage model is briefly presented as well as the parametric identification of the materials that have been used in the reinforced concrete beams. After that, beams with different geometries and reinforcement area are analyzed and a statistical method (ANOVA) is employed in order to identify the main variables in the problem. Soon after, the same procedure is used with another resistance of concrete, where the compression strength is changed. The numerical responses are compared with the ones obtained by Brazilian Technical Code and experimental tests in order to validate the use of the damage model. Finally, some remarks are discussed based on responses presented in this work.

Key Words
damage mechanics; reinforced concrete; technical code; non-linear analysis.

Address
Jose J. de C. Pituba, Rodrigo G. Delalibera and Fabio S. Rodrigues: Computational Modelling of Structures Group, Civil Engineering Department, Campus Catalao, Federal University of Goias Catalao, Goias, Brasil, 75740-020


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