AERODYNAMIC STABILITY OF TRANS-TOKYO BAY HIGHWAY BRIDGE

Of a 5 km-long steel bridge constituting a vital part of the projected Trans-Tokyo Bay Highway, a 1,630 m-long section of 10-span continuous box girder construction containing a main span 240 m in length and 41 m in elevation above the water was analyzed for aerodynamic stability. Wind tunnel testing with a coil-spring-supported two-dimensional model of the box girder cross section showed the girder undergoing galloping and vortex-induced oscillations in the heaving mode in either instance, as predicted by computer simulation. Then, for quantitative evaluation of these oscillations, a three-dimensional aeroelastic model representing the entire 10-span bridge section was tested in the wind tunnel. Unlike the case with the two-dimensional sectional model, only the heaving mode of vortex-induced oscillation, without the galloping vibration, was found to take place. Evidently the adjoining bridge spans abutting the main span, being more slender in girder cross section profile than the latter, served to restrain the vibration-promoting aerodynamic force of the main span. It therefore was decided that addressing only the vortex-induced oscillation would suffice in designing the bridge structure adequately for aerodynamic stability.