Sunday, June 28, 2009

Osaka Bay Bridges: Higashi-Kobe Bridge (2)

The Higashi-Kobe Bridge crosses the Higashi-Kobe Channel in Osaka Bay. Because it's a location of high winds, the weather patterns were carefully studied at the bridge site. The bridge was designed and tested for a 60m/s wind load on the superstructure and a 67m/s wind on the towers. The model was tested in a wind tunnel for diagonal and transverse wind loads.

Because the tower crossbeam is located so low, the tops of the towers had to be carefully designed for wind loads. Among the issues was that galloping of the towers could occur at wind speeds of 20m/s. The solution was to cut the corners of the tower legs. Since the towers were most vulnerable during construction (and before the cables were attached), tuned-mass dampers were installed in the top of the tower legs and raised repeatedly as the towers were built.

The warren truss superstructure was found to perform well for wind loads and the decks were made into structural elements to make the truss stiffer. The cables were covered in polyethylene tubes with ribs to prevent rain-induced vibrations.

Like most cable-stayed bridges, wind controlled much of the design, although seismic loads would probably control if the bridge was designed today.
Creative Commons License
Osaka Bay Bridges: Higashi-Kobe Bridge (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

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