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.