Raising the roof
By Alex Dahm09 January 2009
The Meyer Werft in Northern Germany responded to the increasing demand for cruise liners by increasing one of its fabrication halls by 120 m. It will be able to assemble vessels that are 300 m long and more.
It was decided to build the roof structure close to ground level and then raise it as one to its final position. Heavy lift specialist VSL has used this method many times for aircraft hangars and exhibition halls, but the 76m roof height of the fabrication hall lead the engineers into uncharted territory.
The extension of the hall is made up of 6 frames, spaced at 20 m. First, a massive working platform was assembled about 15 m above ground which corresponded to the level of the annexe building on which the columns are anchored. At one end the roof trusses were preassembled one-by-one and then skidded sideways in steps of 20 m.
To perform the lift VSL (Switzerland) assembled and installed 24 SLU 120 strand lifting units, each with 120 tonnes SWL capacity. Twelve SLU 30s were used for the tie backs.
The load on the lifting units was increased steadily, while the back ties were tensioned in a carefully planned sequence. At the point the roof was hanging free it weighed 2,250 tonnes. The force in the tie back cables was locked and a thorough check of the lifting system and steel structure was carried out.
The weather charts had been studied carefully as the area of Papenburg near to the North Sea can experience relatively high winds. The lift started on 30 August at a speed of 4 mm/sec and in steps of 300 mm. A single operator, aided by a computer, sensors and lasers, ensured the roof remained horizontal and level at all the times, within a very small tolerance.On 31 August the roof was guided into final position. The next day the load transfer procedure was carried out.