Crack opening near reinforcement bars in concrete structures
K. Tammo, Lund Institute of Technology, Sweden S. Thelandersson, Lund Institute of Technology, Sweden
Current concrete codes impose limitations of crack widths at the concrete surface. To investigate how the crack width at the surface affects risk for reinforcement corrosion, the related crack width close to the bar should be determined. An experimental study to investigate how concrete cover affects the crack width at the reinforcement level is presented. Axially loaded concrete prisms with a central 16 mm reinforcement bar were tested. Three different concrete covers, 30, 50 and 70 mm, were used. By continuous monitoring of strains and load, it was also possible to see how the crack width near the bar is affected by crack spacing. The test results showed that the crack width at the concrete surface is more than twice the crack width at the level of reinforcement. The influence of concrete cover seems to be rather small for the crack width at reinforcement level. It was also found that the crack width close to the bar is not affected by short term cyclic variations of five cycles or less with steel stresses in the range 200 - 400 MPa.
Nozomi Bridge - a hybrid structure of stress-ribbon deck and truss
N. Ogawa, Chubu Regional Bureau, Ministry of Land, Infrastructure and Transport, Japan Y. Kamiya, Oriental Construction Co., Ltd, Japan T. Yoshikawa, Oriental Construction Co., Ltd, Japan G. Yu, Oriental Construction Co., Ltd, Japan M. Tsunomoto, Oriental Construction Co., Ltd, Japan
It is well known that one drawback for stress-ribbon bridges can be that significant horizontal reactions at the abutment can be generated and that they have low flexural stiffness. The latter prevents them from being used as roadway bridges. A new hybrid structure of stress-ribbon deck and truss has been proposed and was adopted in the construction of Nozomi Bridge in Japan, a roadway bridge opened to traffic in 2003. Static and dynamic behaviours of the hybrid structure have been studied analytically and experimentally. The results show that the hybrid bridge has advantages over the stress-ribbon deck bridge as it generates much less horizontal force in suspension cables and has higher flexural stiffness, suitable for use as a roadway bridge, and that the hybrid bridge has advantages over the truss bridge since it can be constructed without extensive falsework and without large erection equipment. In this paper, at first, the hybrid structure is described, then analytical and test results are used to show its static and dynamic characteristics, and finally the construction of Nozomi Bridge is outlined.
Cracking analysis of reinforced concrete tensioned members
S. Khalfallah, University of Jijel, Algeria
An analytical model, which can simulate the cracking response of reinforced concrete tensioned members, is presented. This model is principally based on the bond stress-slip repartition function that was successfully applied to the analysis of tensile reinforced concrete members. The formalism of repartition functions of loads, strains and slip between steel and surrounding concrete, has allowed analysis of the cracking phenomenon and its influence on the structural behaviour of reinforced concrete members. The tension stiffening effect accompanying the cracking mechanism is taken into account in a more appropriate manner. The phenomenon of localisation of micro-cracking owing to the softening behaviour of concrete in tension is based on the conservative concept of the cracking fracture energy assuming that the band of strain localisation is an intrinsic parameter of the material. The predictive results show that the model is very satisfactory, allowing the evaluation of each material contribution especially in the cracked range. Moreover, a correlation between the obtained and experimental results is observed through the local and global responses.
Report on the First fib Congress 2002, Osaka, Japan
T. Yoshioka, Oriental Construction, Japan T. Mori, P.S. Mitsubishi Construction, Japan A. Kasuga, Sumitomo Mitsui Construction, Japan T. Miyagawa, Kyoto University, Japan
With a theme of "Concrete Structures in the 21st Century", the First fib Congress was successfully held in Osaka, Japan. Organised jointly by the Japan Prestressed Concrete Engineering Association and the Japan Concrete Institute, the Congress ran from 13th October to 19th October 2002. This report introduces the Congress and confirms that it has enabled us to envisage the prospects for concrete structures in the 21st century.
A. Kasuga, Sumitomo Mitsui Construction Co., Ltd., Tokyo, Japan
Extradosed bridges are similar to cable-stayed bridges in that stay cables are used for strengthening. The concept of extradosed bridges has been taken up in Japan, where several bridges of this type have now been constructed. This paper shows five extradosed bridges that were designed and built by the author, and explicates the difference between extradosed and cable-stayed bridges in terms of structural aspects. In addition, the method of design for stay cables in Japanese specifications is introduced.
Bond clause proposals for FRP-bars/rods in concrete based on CEB/FIP Model Code 90. Part 2: Design lengths and tension stiffening
R. Tepfers, Chalmers University of Technology, Göteborg, Sweden
The bond clauses in the CEB/FIP Model Code 1990 (MC90) were written for steel reinforcement in concrete. Since then, fibre reinforced polymer (FRP) reinforcing bars have been introduced as an alternative. To make use of fibre composites, it is necessary to bring these materials into codes of practice and the easiest way is to adapt the code clauses for steel reinforced concrete to FRP reinforced concrete. Proposals for the design bond stress code clauses have been presented in an earlier paper. This paper covers proposals for the design lengths and tension stiffening code clauses.
