Dynamic wall loads in grain silos

The problem of the pressure distribution in a reinforced concrete silo exhibiting funnel flow was considered when the GRAINCO Queensland Cooperative Association Limited approached the Mechanical Engineering Department of the University of Central Queensland after a series of aeration duct collapses had occurred in the silos at Gladstone Grain Terminal, Central Queensland, Australia. Initial investigations indicated that only Jenike, Johanson and Carson had developed a procedure for computing the peak pressure at the switch in concentric funnel flow silos, and only a few sets of experimental results taken from full scale funnel flow silos were available. Research to date has concentrated on the pressure distribution on the hopper walls of a funnel flow silo, particularly in dynamic condition. In this investigation Jenike' s funnel flow theory was followed. Design codes AS3774-1990 and ACI313-77 were evaluated. Special pressure transducers were designed and made to measure the normal pressures exerted by grain on the concrete walls of the containing silo. This investigation experimentally determined the pressure profiles on the hopper walls of the funnel flow silo during filling and discharge conditions. Normal wall pressure records indicated that unstable flow patterns were developed in the silo. Repeating dynamic overpressures were recorded on the hopper walls at random intervals after discharge from the silo had begun. The experimental results were compared with existing funnel flow theories and codes of practice and were presented in the form of graphs suitable for the immediate application to design practice.