Risto Kiviluoma, Technology Director, WSP in Finland
The main challenge in wind engineering was not the size of the bridge itself but the site and altitude at which it is located. In extremely rough topography, standard models of wind and turbulence are unlikely to be realistic; a special type of wind tunnel testing was therefore conducted to assess the design wind parameters.
Wind engineering of the bridge was conducted by combining in-house wind engineering expertise and the wind tunnel tests of FORCE Technology in Denmark. The first test involved a large-size topography model of the bridge site. It revealed some unusual wind characteristics, including up to 11 degrees vertical inclination of the mean wind velocity and wide scatter of turbulence intensity from 7 percent to 55 percent, depending on wind direction.
The next test in the program was standard section model testing, which contributed updated aerodynamic input to WSP’s advanced 3D buffeting analysis and equivalent static wind load extraction. Buffeting results were further confirmed with full aeroelastic model tests.
Subsequent design changes and construction stages were assessed computationally, i.e., without extra testing.
Thanks to truss structures in the arch and the piers, the bridge is not sensitive to aeroelastic instabilities, but the lateral wind load itself was of main interest. This was due to the need to control lateral displacement of the deck for smooth railway operations.
The construction site has so far been free of major storms, though during the 120 years of design service life of the bridge they will likely occur. Continuous surveillance of wind conditions and a warning system will help manage rail traffic.