A combination of hydraulics, variable speed drives and PLCs, helped to raise the spectacular arched roof over the main stadium at the Athens Olympics. The 10,000m² metal and glass roof is suspended from two giant steel arches, each spanning 304m and soaring up to to 80m above the ground.

The two halves, each weighing 8,500 tonnes, were assembled on either side of the stadium, about 70m away. They were pulled into position at an average speed of 85mm/min, to an accuracy of ±2mm, in a complex operation that took place during May and June.

Two groups of four hydraulic cylinders (see below) were used to pull the giant structures, with each group powered by a two-stage PLC-controlled pump. Each 1,300kg cylinder had a stroke of 2,000mm, operated from a pressure of 600 bar, and delivered a maximum pulling force of 150 tonnes.

The pumps` PLCs were linked by 400m cables to synchronise their movements. To ensure that all movements started and stopped smoothly, the pump motors were controlled by variable speed drives, supervised by the PLCs.

Although there had been doubts whether the roof would be raised in time for the start of the Olympics, the job was completed in time to protect the athletes and up to 75,000 spectators from the sun and the rain.

The hydraulic equipment was supplied by Enerpac, which has also been responsible for several other spectacular projects recently, including the world`s tallest road bridge, in France.