Effects on Aerodynamics of Long-Span Bridges with Different Vertical Clearance Under Bridges Decks

In order to investigate aerodynamics of long-span bridges with different vertical clearance under bridges stiffening girder, the Reynolds-Averaged Navier-Stokes Equations and SST k-ω turbulent model were employed to solve the flow field around bridge girder of the Great Belt East Bridge main span with different vertical clearance in natural wind. The aerodynamic coefficients under various vertical clearance is presented and compared to wind tunnel test, and its flow mechanism relating to those changes is analyzed.
The results find that the variation of vertical clearance presents mix effects on pressure distribution on girder surface, on lift and drag acting on girder, and on vortex shedding S_t number. When the vertical clearance decreases, the lift and drag coefficients will increase. Compared to the results from vertical clearance of 5B, the vertical clearance of 0.4B produces an increase of 87.8% for lift coefficient and an increase of 13.3% for drag coefficient, and the vortex shedding S_t number also indicates slightly increase. The monitored pressure distribution on girder surface indicates that when the vertical clearance is small, the peak pressure at the positive zone ahead of leading edge of the girder increases, and the peak negative pressure at the windward corner of the deck and bottom also increase, with significant increase observed at the deck corner. It is concluded that when the vertical clearance under the bridge is very small, the water surface will generate significant aerodynamic interference to the bridge girder, hence the increase wind loads acting on the bridge girder due to significantly small vertical clearance should be considered as to insure bridge safety against wind.