Design and construction of the Metrolink Finback Bridge

Abstract

The Manchester to Oldham line of the proposed Metrolink Phase 3 passes through the new Central Park business park utilising the existing track bed of a disused and dismantled heavy rail route. To the east of Thorp Road Bridge the new Metrolink route crosses the existing four tracks of the Manchester to Leeds Trans-Pennine railway. A post-tensioned concrete finback bridge has been provided to carry the new twin Metrolink tracks over the existing heavy rail route. In order to minimise disruption to the operational railway, the Finback Bridge was constructed in a position alongside and roughly parallel to the existing railway. Once the construction was substantially complete, the 6250 t bridge was rotated in plan through 21° to its final position during a weekend possession. The site constraints resulted in a reverse-curved horizontal alignment with the consequential requirement to cater for significant torsion in the design of the deck. The deck solution was a box section finback bridge with varying fin height and fin wall thickness. The bottom slab of the box was extended to cantilever outside the central fin to support the Metrolink tracks. The superstructure incorporates two types of post-tensioning; internal bonded tendons in the deck slab of the main span and external unbonded tendons located inside the fin.