Bridge operation and constraints

The initial consultation responses made clear it was important to maintain access to the dock area for leisure activities and to ensure that larger vessels can still access the dock once the new bridge is built. The responses also included a wish for the new bridge to be swift to open and close.

The bridge opening mechanism and span will allow for a 25m wide navigation channel with infinite headroom that will guarantee accessibility to the dock for larger vessels when the bridge opens. It is expected that the bridge will open twice a week as an average. The closed bridge will guarantee a 15m wide and 3m high permanent navigation channel that will allow for some leisure activities.

The movable bridge type that has been selected (bascule bridge) is commonly known as the fastest of all the mechanical options. However, the opening speed doesn't only depend on the mechanism but also on the time to clear the bridge of pedestrians before it opens. Design decisions, such as the use of hydraulic cylinders or a counterweight that fully balances the weight of the main span, improve the opening speed compared to other solutions. It is estimated, at this stage, that it would take 90 seconds for the bridge to open or close. However, the whole cycle will include other activities such as the time to open and close the gates, to clear the bridge deck or for the vessel to pass through.

The potential impact of east-west cross winds on the bridge were raised as part of the initial consultation. The latest design is more compact, with a smaller vertical envelope exposed to wind, especially in the area that is less sheltered by the buildings. The main span now has an A-shape design that provides a more natural structural layout to transverse wind loads, especially in the open position.