A study of the influence of wall flexibility on pressure in rectangular silos

Abstract

The pressure cxcrtcd by the stored material on rcctangular planform flexible walled silos is investigated during filling and discharge. Tests on a large scale steel model silo with a pyramidal hopper showed that the stress state of the stored material is significantly influenced by the wall flexibility and boundary conditions. The measured wall pressures were very different to pressures predicted by traditional theories and existing design codes. This is because traditional theories were developed for rigid walled circular silos and they ignore the effects of stored material/structure interaction. In this thesis the results of tests to measure the stress state throughout the contents of a flexible silo and pyramidal hopper are presenteda nd compared with measurementso f the structural response. The tests show that the redistribution of stresses within the stored material is cxtcnsive and is influenced by the corners in non-circular silos and horizontal and vertical stiffeners. As wall flexibility increases, the ereis increased freedom for stresses imposed by the stored material to redistribute and reduce the structural forces in the wall. The measured pressure in the corners of the model silo were up to nine times the pressure as the centre of the wall at the same level. The failure to incorporate the redistribution in to the model design led to a considerable over estimate of the wall stresses. Many existing measurements of pressures in the stored material in silos were weakened because of inaccurate instrumentation. In this study. considerable care was taken during the selection of pressure cells. Calibration and equilibrium checks to ensure the accuracy of measured data. Pressure was measured in four directions at forty eight positions in the model to determine the total stress state throughout the stored material. The results showed that wall pressures were influenced by five different arching phenomena. It is concludedt hat the cxisting theory is not accurate for pressure calculation in flexible non-circular silos. The use of a more accurate theory for the calculation of wall pressure can lead to extensive savings in the cost of the silo structure.