Benefits and Challenges of the Twin-box Bridge Girder

The aerodynamics of the twin-box bridge is considered to highlight the reasons for making this type of bridge deck superior to the conventional trapezoidal mono-box for suspension bridges having span lengths longer than 1800 m. The paper proposes a simple theoretical model yielding physical insight into the flutter stability and presents a design example comparing the flutter performance of a 2000 m main span suspension bridge designed with either a mono-box or a twin-box bridge girder. Experience from vortex induced vibration of twin-box bridges is discussed to demonstrate that a twin-box girder can be designed to avoid vortex induced for practical damping levels.