AERODYNAMIC BEHAVIOUR OF A SPLIT BRIDGE DECK SECTION FOR LONG SPAN BRIDGES

摘要

With the increase of the span of suspension bridges, aerodynamics plays an ever-increasing importance in the selection of a deck profile. Functionality requirements of a suspension bridge dictate that it must not only span lengths of over 2000m, but also must be able to facilitate multiple uses, such as rail and vehicular traffic. A new shape of split bridge deck consisting of multiple sections, which would confer a better stability against wind induced vibrations, was aerodynamically investigated. The deck consists of two traffic lanes on the exterior sections and two railways on the middle sections, separated by three gaps. Airflow simulations were performed on a reduced scale model at a Reynolds number of 8×105 for angles of attack -5°, 0°, and 5°. The airflow around the multiple-gap deck section was more complicated, with the flow passing through the gaps, shifting from the top of the deck to the bottom and vice versa. The effect of turbulence was modelled by 2D Reynolds Stress model. A triangular mesh with a no-slip boundary condition for the bridge deck was used. With the increase in the number of gaps along the width of the proposed bridge deck, a more unstable pressure distribution on both upper and lower sections of the bridge decks was observed (CP = -0.8 to 1.0) when compared with the standard split bridge deck. A significant reduction of aerodynamic lift force, which is responsible for inducing vibrations, was registered. The most unfavourable combination of aerodynamic drag and lift forces was registered for angle of attack of 5°, for both types of deck sections. The proposed split deck outperformed the standard split deck when tested under same wind flow conditions, providing better stability in terms of reduced lift coefficients along with the reduction in the drag coefficients.