For U2’s 360° Tour the Belgian company, Stageco constructed three gigantic, identical stages. What made this project special was that high pressure hydraulics were used for the first time ever to assemble and dismantle the 230 ton construction. Together with Enerpac, Stageco developed a unique system based on Enerpac’s synchronous lift system to raise the modular construction to a height of 30 metres quickly and safely.
The steel stage construction consisted of a central lock which rested upon four legs, each made up of six sections. The central block was gradually lifted off the ground in 38 steps and a section was added to each of the four legs after every six or seven steps. A temporary truss containing a supporting frame at the top was made for each leg. Within each truss was a hydraulic pump unit, four high pressure lifting cylinders (350 bar), each with an applied pulling force of 20 tons and a 600 mm stroke, and four 0,5 ton low pressure (60 bar) locking cylinders, each with a stroke of 260 mm. All were attached to a supporting frame, which moved along the guide rails. The complete hoisting system for each stage therefore consisted of 16 lifting cylinders, 16 locking cylinders and four fully hydraulic units. The lifting cylinders were fitted with a pressure transducer, a built-in stroke sensor and two proximity switches. The locking cylinders were also fitted with two proximity switches. The hydraulic pump unit included individual pumps – one for the lifting cylinders and one for the locking cylinders. The pump units were controlled according to the master/slave principle from a central operating computer on the ground, which had a touch screen with images showing the position of the various hydraulic cylinders and their position within the lifting portals. The force of each lifting cylinder and each lifting portal was also displayed, along with the total force. A local PLC was installed on each platform so that the lifting platform could be operated locally if necessary.
First of all, the complete pump units were positioned in the lifting portals using a small mobile crane. At the beginning of the lifting process, the ends of the central block rested on the supporting frames with the Enerpac units. When the frame was lifted, the top beams were first raised one step hydraulically, and then locked mechanically using locking pins and the hydraulic locking cylinders. The bottom locking pins were then cleared hydraulically and the cylinders raised the load to the same height. In this way, the four hydraulic units lifted themselves in the lifting portals with the load, as it were, at a net speed of around 10 metres per hour. Lift synchronism was vital here due to the torsional stress that occurred. Stageco worked with a tolerance of 5 to 10 mm. This may seem like a lot, but it was adequate since the lifting portals were 35 metres apart. The operating computer’s display also showed that the load in the four portals remained in perfect balance. The display showed which steps in the lifting process had already been completed. The operator did, however, need to give the system a command for each step. After the claw was assembled, the pump units were lifted out of the lifting portals with a crane and the lifting portals were then removed. The system worked according to the same principle but, of course, in the opposite direction when the whole construction was later lowered and dismantled. The pump units were then back on the ground and could be stored ready for transport to the next location.
Stageco made no concessions whatsoever as far as safety was concerned. The mechanical locking of the lifting platforms, for example, was an extremely important element. Enerpac’s computer-controlled synchronous lift system also fulfilled this requirement perfectly. Every step in the lifting process was controlled, and the next step could only be performed when all the required conditions had been fulfilled. The system also gave information on the position the load was in, and how the tension was distributed during lifting. The Enerpac system measured the forces continuously and in real time. Although the operational speed was significant, Stageco considered safety to be one of the greatest advantages of this technology. Since the three stages travelled across the whole world over two years, the emphasis was also on reliability and durability. According to Stageco, another advantage was that Enerpac had an international presence and operated worldwide.
Enerpac is represented locally by BMG.
For more information contact Lauren Holloway, BMG, +27 (0)11 620 7597, [email protected], www.bmgworld.net
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