National Highways has modelled plans for a new central reservation barrier on the M4 Prince of Wales using a wind tunnel.
The government-owned company was able to virtually observe the effects of wind on the bridge model in a controlled and recorded bridge tunnel environment.
It was determined that ‘the bridge with the new solid median will behave virtually identically to the bridge in its current state’, allowing steps to be taken towards onsite construction in 2025-26.
The national operator said that while replacing steel barriers with concrete is normally straightforward, the environment of the 5,128-metre bridge across the Severn Estuary provided a unique challenge.
It needed to understand the impacts of a concrete barrier on the 948-metre cable-stay section of the bridge, which is subject to strong winds and a challenging marine environment.
This section can be particularly sensitive to wind-induced oscillation if changes are made to the road.
National Highways’ Specialist Bridges Group carried out a feasibility study project as part of its development stage, aimed at modelling and assessing the aerodynamic stability implications of installing a new concrete barrier.
Matthew Jones, asset needs and programme development manager for the Specialist Bridges Group, said: ‘By undertaking modelling, trials and tests like these, we can ensure we’re making the right changes to see significant long-term benefits and improve the experience of our roads for motorists.
‘Upgrading these barriers will improve journeys and significantly reduce the risk of vehicles crossing over from one carriageway to another.’
The project involved innovative wind testing techniques in Canada with specialist consultant RWDI, which has worked on other famous structures such as the Golden Gate Bridge.
This allowed the proposed barrier design to be tested under different wind conditions and scenarios, whilst factoring in the specific dimensions and cross-section profile of the Prince of Wales Bridge.
The 1:70 scale model of the Prince of Wales bridge for the wind tunnel testing
Patrick Madden, designer for Amey, said: ‘Upgrading the existing barrier to bring it in line with current standards is vital, and it has a significant impact on maintenance requirements of the barrier.
‘The current barrier requires partial closures of the bridge for ongoing maintenance, and these interventions can impact the bridge structure itself as the current barrier is bolted to the deck.
‘The proposed barrier will require significantly less maintenance, as it is less prone to damage that requires interventions, and it does not require mechanical fixing to the deck, reducing the impact on the bridge structure when maintenance is required.’
