The unique topography of the area also prompted a full-model test including models of the mountainous topography surrounding the bridge. Wind tunnel tests conducted during construction as well as completion Since safety of the project during construction as well as at completion was important, wind tunnel tests were conducted in both instances. Tests were made on the two towers in both a completion and erection stage.
These precautions were rewarded with a perfect safety record of no accidents during the entire six-year construction phase. Of particular interest was the finding that the aerodynamic stability of the towers during erection was effected by scaffoldings. When the erection scaffolding in the tower top was removed from the tower shafts, galloping vibration on first bending mode was induced.
As a result, scaffolding contributed to stabilization of the galloping. It was determined that the increase in the draw coefficient of the tower shaft, the turbulence intensity of the wind, and the axial flow were possible reasons for the suppression of the galloping vibration. As a result, in spite of the fact that the tower is meters tall and no damping devices were installed, aerodynamic stability of the tower was secured when all scaffoldings were attached. The integrity of the precautions was proven on three occasions when typhoons hit during construction with no mishap.
Other factors tested throughout the project included the girder buckling and elastic support, the tower shape and the cable design. Of particular interest were the cables, which were installed in a fan shape with two planes of 21 rows of cables fixed to each side of the towers.
The cables were made of semi-parallel wire strands consisting of galvanized wires 7 mm in diameter covered with polyethylene tubing. The longest cables consisted of wires, were m long and had a diameter of mm. Special cable surface used to improve aerodynamic stability To counteract "rain vibration," a typical wind-induced cable vibration associated with wind and rain, the cable surface was indented or "dimpled" to improve aerodynamic stability. This was the superior method determined after also testing two other methods which included connecting the cables with wires or increasing the logarithmic damping of the cables by installing damping devices between cables and girders.
Two aerodynamic countermeasures of mitigating the vibration by processing the surface of the cable surface included "protuberance cable" and "indented cable. Another questions concerned the length of construction, which the builders noted was particularly long due to the necessity to draw the financing from various sources. Future bridges should be built in less time, the builders said. An inquiry was made also as to whether or not the construction costs could be cut due to the extensive time-consuming and "money-consuming" testing that had already been done with the Tatara project.
The answer was that it was hoped that much information will profit future projects, but testing will still need to be done. Moderating the presentation was Kazuhiko Kawashima, professor, department of civil engineering, Tokyo Institute of Technology. He may be contacted for more details at kawasima cv.
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