Measurement of imperfections in full-scale steel silos

Small imperfections in the walls of steel storage tanks and silos can influence both the buckling strength of the wall and the incidence of local high pressures on the wall due to bulk solid compression. Few measurements of these local imperfections have ever been made on silos in service, chiefly because the task is extremely difficult using conventional techniques. This paper describes an innovative new system for the measurement of imperfections in the walls of steel silos in service. It combines observations from conventional survey instruments with those of a new wall profile measurement apparatus. This new apparatus is a trolley which moves over the wall surface and simultaneously observes horizontal and vertical profiles on the structure. The paper describes the design and measuring procedures for the system. The three-dimensional shape of the structure is defined by combining the profile measurements with conventional survey observations in a rigorous XYZ coordinate system. The application of the system to the measurement of imperfections in some full-scale steel silos is described, including some preliminary results showing the measured shapes and their estimated precision.