Hoisting the roof, mountain-climber style
14 Sep 2015
-
R.A.
In order to climb the face of steep cliffs, mountain climbers use a clever device, invented in the 1950s, called a "rope ascender." Also known by its brand name Jumar, the device can be compared to a mechanical hand that can slide up a rope but that is prevented from sliding down by a locking clamp.
A similar mechanical principle was used, last Thursday 10 September, to lift the steel roof structure of the ITER Assembly Building. Since April, construction contractors had been assembling the 730-tonne structure on the ground to be lifted as one piece.
Centimetre by centimetre, over the course of 14 hours, 22 hydraulic jacks hoisted the huge structure along thick steel cables that hung from support structures fixed temporarily to the top of the pillars, 60 metres above the surface of the building's basemat.
The operation had to be carried out with extreme care. The structure, measuring 60 metres long and 25 metres wide, had to be precisely positioned between two rows of vertical pillars, with a tolerance of only a few centimetres on each side.
It began with a mere 20 cm lift in the morning of Wednesday 9 September, followed by precise laser metrology to measure potential deformation of the steel structure. By Thursday morning, all systems were go, the wind below the 11 metre per second safety limit and the 50-metre lift could commence.
The successful lift operation had a high symbolic value for the ITER Project. "It is here, in the antechamber of the Tokamak Complex, that the main components of the ITER Tokamak will be prepared and pre-assembled," explained ITER Director-General Bernard Bigot in the short speech he gave prior to cutting the ribbon. "Without this building there would be no assembly, and without assembly there would be no machine and no project..."
The ceremony was broadcast live to the ITER staff assembled in the Headquarters amphitheatre and by video feed to the ITER community throughout the world.
The construction milestone demonstrated, once again, the value of close collaboration between all project stakeholders. Under the authority of the European agency for ITER (Fusion for Energy), more than a hundred workers, engineers and technicians worked in shifts for the success of the operation.
"The months and years to come will continue to demand effort and dedication from all of us," said Director-General Bigot, "but we are all conscious of working for one of the greatest ventures in the history of mankind, one that could change the course of our civilization..."
As the ribbon was cut, 500 ITER-yellow and European-blue balloons slowly ascended to the top of the structure and out to the clear sky. The "house" now has a roof and the ITER family is impatient to move in.
In sync with the roof, by the end of the day on Friday 11 September the clouds had lifted. The completed steel structure of the Assembly Building adds a spectacular new feature to the ITER worksite.
Posing for a group picture under the Assembly Hall roof are staff members from the Buildings, Infrastructure and Power Supplies (BIPS) Project Team, architect-engineer Engage, APAVE (safety specialists), Martifer (steel structure assembly), and VSL (heavy lifting).
Just as this picture is snapped from the roof of the ITER Headquarters building, balloons are released in celebration from the Assembly Building basemat. Photo Nicolas Tourniaire
First Plasma may still be years away, but some helium was present on site on 11 September. Five hundred yellow and blue balloons, for the colours of ITER and the European Domestic Agency respectively, were released at the end of a small celebration marking the construction milestone.
ITER Director-General Bernard Bigot cuts the symbolic ribbon as the site manager for the European Domestic Agency, Laurent Schmieder, looks on. The ceremony is broadcast live to staff assembled in the auditorium of the Headquarters building and accessible by way of video feed to the Domestic Agencies.
Prior to the ceremony, Director-General Bernard Bigot speaks with the workers involved in the heavy lift operation.
The 14-hour operation to lift the roof structure of the Assembly Building into place was successfully completed at around 4:00 a.m. on 11 September.
5:00 p.m. on 10 September: it takes 22 powerful hydraulic jacks, working at only 30% of their capacity, to hoist the roof into its final position. The principle is the same as that of "on-rope ascenders" used by mountain climbers.
At a first height of 30 cm, the roof structure was stabilized and left to hang for 24 hours to measure potential deformation. Then, the 22 hydraulic jacks pulled on the cables over the course of 14 hours to lift the structure to a height of 50 m. (In the photo, the structure is part way there, at 20 m).
As the roof structure inches towards the top of the pillars, technicians from VSL, the company in charge of the lifting operation, perform real-time laser metrology to measure its position.
The lifting speed is so slow (4 to 5 metres per hour) that it's not perceptible to the eye. But one can hear the regular sound of the hydraulic fluids pumping into the jacks.
The event interests media from near and far. European site manager Laurent Schmieder and his colleague Miguel Curtido provide technical explanations to a TV crew from the French regional TV channel France 3.
Early on the day the operation starts, ITER Director-General Bernard Bigot, site manager Laurent Schmieder (from the European Domestic Agency) and foreman Dhaoui Sif perform one last check before the operation can begin.
The golden hour
8:00 p.m. on 9 September. As the Sun sets, a golden hue settles over the ITER worksite. The roof lifting operation is set to begin on the following morning.