ROOFTOP DRAMA: Built in 1974, the 143m high Selmi tower in Frankfurt, Germany is currently being refurbished by contractor Hochtief. But with part of the work on the now named City House involving addition of an escape stairway on the outside of the building, the tower crane required for construction work could not be anchored to the outside as usual. Instead the Liebherr 71C was mounted on the roof, erected from the air. The operation, planned and carried out by Streif Baulogistik, took just three hours using a chartered Kamov heavyduty helicopter. The crane stands on a cruciform foundation measuring 3.8m by 3.8m, made up of two 12m tower sections and a 33.4m jib. Modules weighed between 1,500kg and 4,100kg, well within the capacity of the Kamov which can lift up to 5000kg.