ABSTRACT
The first prefabricated elements in tubular scaffolding were roof trusses of various sizes and shapes. The necessity for these was that when trusses were made of tubes and couplers, the ends of the tubes and the bolts on the couplers spoiled the top surface of the truss for receiving the sheeting. It was soon realised that these trusses could be used as beams either the correct way up or upside down. The next stage in development was to cut off the apex of the roof trus», leaving a very useful trapezoidal beam which could be used either way up. When used upside down, it became the normal fish-bellied beam still used to the present day, but losing favour to the ladder beam and the unit beam.
