Aware that traditional steel arch bridges with vertical hangers can fall foul of the Eurocode pedestrian dynamics requirements, the design team proposed a 42m-long bowstring truss for the main span section.
Pedestrian dynamics needed to be carefully considered as they had to achieve sufficient stiffness to avoid lateral vibration.
Another important consideration for the construction programme and design teams was the busy A4440 and the need to minimise disruption to the thousands of vehicles that use the road daily.
The assembled main span was installed during a Saturday morning closure of the A4440, using a self-propelled modular transporter (SPMT) to move and position the superstructure.
The installation was extremely quick and it enabled the roundabout to be reopened within two hours, before the peak Saturday morning traffic period.
According to COWI, the project’s engineer: “Steelwork was chosen as it allowed the entire superstructure to be prefabricated offsite for a high-quality finish, and then, once delivered to site, it could be rapidly installed.”
The main span of the bridge exceeded road transportation limits and so it was delivered to site in three sections. An assembly jig was constructed close to the main span’s final position to allow the three sections to be site welded together.