Steel Scaffolding. Discussion on Mr. P.M. Andrews's Paper
Mr. Andrews, in presenting the paper, took the opportunity to put a number of questions to members, in the hope that, answers might be given during the discussion. After stating that he had no connection, either directly or indirectly, with any scaffolding firm here or abroad, he pointed out that the tubes were designed originally for the conveyance of steam, water or gas, and, therefore, were designed to withstand continuous internal pressure. As we were using precisely the same tubes in scaffolding and were using them as columns, we were subjecting them to a form of pressure entirely different from that for which they were designed. His first question was whether the 6-gauge weldless tube was as satisfactory as the ordinary welded tube when used as a column. Secondly, the hollow tube, used as a column, was a very good section provided that, the load on it were concentric, but if the load were applied eccentrically the hollow steel column was about the weakest section possible.
Therefore, he asked whether it was possible to load such columns concentrically. The tubes were fixed together by means of couplers, so that each coupler conveyed the load to the tube, and there seemed to be a distance of about 2 inches from centre to centre; therefore, the eccentricity on the column should be 2 inches. He had calculated that a 1 1/2 in., 6-gauge tube, 6 ft. long, used as a column, would carry about 2 1/2 tons if loaded concentrically; but the moment it was loaded with an eccentricity of 2 ins. it would carry only about 9 or 10 cwts. That seemed to be rather
important in considering the design of steel scaffolding, and he hoped that an expert would describe the eccentricity on the tube and a means of overcoming it; he believed there were methods of overcoming eccentricity in steel scaffolding.