The Paddington LTVA project includes the replacement the existing Bishops Bridge over the entrance to Paddington Station, London, with a new wider structure to improve access to the station. The old bridge consists of a 60m span truss over 10 tracks, a 3 span structure over a further 5 tracks and a series of short spans crossing open ground and the Grand Union Canal. The construction method, chosen to minimise disruption and risk to rail traffic, involved lifting the truss span on jacking towers to allow replacement of the substructures and launching of the new bridge deck underneath. The existing bridge, weighing 941 tonnes, was lifted in August 2004 using 4 No DL-S418 strand jacks (see photo below) and the new deck was launcged beneath it in 2005.
Headroom and highway alignment constraints have dictated the superstructure form of multiple variable depth plate girders supporting a skewed reinforced concrete slab. The deck shape has resulted in the need for a complex system of height adjustable rollers and supports for the launch of the new deck. The new bridge, 105m long with a launch weight of 2500 tonnes, is was launched down a variable slope using 4 No DL-S418 strand jacks, 2 No to pull the deck and 2 No to restrain the deck from running away down the slope. Hydraulic jacks are used at all launch roller support positions to continuously adjust the roller height and support load distribution throughout the launch.
At the intermediate pier position under the main span, between rail tracks,
the deck was temporarily supported on a roller system that is in turn supported
on 8 No DL-C450 climbing jacks that were used to vary the roller support
level by 5 metres during the launch. Launching of the new deck was carried
out in 21 No 3.5 hour overnight rail closures. All strand jacks and climbing
jacks were controlled and synchronised by a single operator using the DL-P40
computer control system.
DLT were responsible for all the conceptual and detailed construction engineering and temporary works design, and for the supply and operation of all the jacking systems.