Nestling between an existing motorway bridge and a newly constructed railway bridge, a new road bridge is being constructed across the river Medway in Kent, in the southeast corner of England. The new bridge will help increase highway capacity at a pinch point between London and the Channel Tunnel.
Specialist contractor Dorman Long Technology (DLT) was brought in to lift two 720t falsework trusses to a height of 28m, then to hold them in place while concrete was cast in situ for the new bridge’s 80m post-tensioned side spans, before finally lowering the trusses again. For the task, DLT used eight of its 100t capacity hydraulic climbing jacks.
Climbing jacks have many of the capabilities of strand jacks but the main difference is that with a climbing jack system the load is transmitted to a square bar in compression rather than strand cables in tension with the strand jacking system. Climbing jacks have the advantage when the load path needs to be kept beneath the load being lifted, as was the case over the Medway.
The square climbing bars were fixed to the bridge piers at each end of the span and the load of the lift was transferred down onto the tops of the pile caps. Using climbing jacks saved about 12 weeks on the contract programme, DLT claims, as strand jacks would have had to be repositioned several times and would have needed a separate support system.
On this project DLT carried out full engineering and design, supply and installation of temporary works, and the supply, installation and operation of the jacking equipment for joint venture main contractor Costain Skanska Mowlem. DLT also did other jacking work on the project, including the erection of travelling formwork on the cast in situ balanced cantilever main spans.
DLT has two sizes of climbing jack, 100t and 400t capacity units, that can be used individually or together in multiples. Each unit consists of an upper and a lower wedge unit connected by a pair of solid hydraulic rams. The wedge units grip a square section steel climbing bar and operate with the jacks to move along the bar.
Dorman Long Technology was formed in August 2000 when Dorman Long, part of the Cleveland Group, acquired the engineering design divisions of Cleveland Bridge UK and Lowther-Rolton International, together with the jacking and heavy lifting specialist Zalcon.
Other recent projects include the erection of three container crane superstructures in Tianjin, China last October using eight 185t capacity strand jacks. The jacks were computer controlled for synchronisation, load and speed. The ship-to-shore container cranes, manufactured in Argentina by IMPSA, have a total hoisting height of 50.5m and the maximum height from the hook to the top of the quay is 32.5m.
