The Aberdeen Western Peripheral Route/Balmedie to Tipperty (AWPR/ B-T) project is a major infrastructure project being delivered by Transport Scotland in partnership with Aberdeen City Council and Aberdeenshire Council. Extending northwards from Stonehaven to Tipperty, the new 58 kilometre road fully opened to traffic on 19 February 2018.
The road is expected to remove traffic from the city, as well as rural and urban local roads, which will reduce congestion and improve journey times as it bypasses the city of Aberdeen.
The bridge over the River Don, one of the major crossings on the project, required a H4 parapet along both edges of the 300-metre length of the bridge. The method of constructing the concrete plinths supporting the parapets had to be quick and agile in meeting the requirements of the construction programme.
Precast concrete was initially considered as a way of saving time. This decision was later changed to cast in-situ, as it was quicker to pour the concrete on site than erect, install and stitch precast segments to the in situ portion of the deck. For in-situ casting to take place, a project-specific formwork traveller was required which would ensure fast, yet safe construction of the parapet and coping.
What was the challenge?
As with anything visible to the public eye, ensuring a unified and visually appealing finish was important throughout all elements of the bridge. In addition to the specified concrete finish, the formwork solution had to provide access to the underside of the bridge deck, enabling workers to pour concrete for the coping.
Balfour Beatty & Galliford Try
Transport Scotland / Aberdeen City Council
We designed a bespoke cantilevered parapet carriage to meet the geometry of the bridge deck using off-the-shelf VARIOKIT components and roller units. By using standard components, we were able to minimise waste throughout construction of the parapet, as the system could be adapted, dismantled and reused.
In total, four carriages were used simultaneously to facilitate the concrete pour, two on either side of the bridge at each end. We embedded steel profiles within the bridge deck to ensure the systems moved smoothly.
Once the concrete had cured, the systems were winched along the bridge deck to complete the next pour, eventually meeting in the middle on completion. A carriage was capable of concreting a 25-metre-long section at each pour before moving on to the subsequent section.
We also incorporated secure, hand-railed working platforms with the carriages. The platforms provided safe means of access for workers when pouring concrete as high as 40 m in areas that were difficult to reach.Prior to concreting, the systems were also used for the installation of reinforcement bars that were added to strengthen the concrete. By casting in-situ using the parapet carriage, the customer was able to save time on the project, which would not have been possible using precast concrete.