Seminar - Alvaro Ramirez - Pressure measurements in full-scale steel silos
Wednesday 2 May 2007, 1.10 - 1.50 pm
Civil Engineering Lecture Theatre 3
Many problems have arisen due to failures of silo structures. For more than a hundred years researchers have studied these problems by means of theoretical, numerical and experimental studies. The theoretical and numerical studies need to be calibrated and validated using information obtained from experimental studies. However, the complexity and the costs of the experimental installations have limited their number. Therefore, there is still a lack of data for developing necessary understanding of phenomena that occur inside the silos (Brown and Nielsen, 1995). Many different types of experimental silos have been studied throughout the world since the first tests carried out in model silos made of wood (Janssen, 1895).
The present study shows the initial results from pressure measurements in an installation of three metallic full-scale silos. These silos are made of a conical roof, a cylindrical part and a conical hopper with different eccentricity (0%, 50%,100%) for each one. The cylindrical part has an aspect ratio of 2.5 (height 5.0 m, diameter 2.0 m) and the height of the hoppers are 1.6 m and have a circular outlet with a diameter of 0.32 m.
Pressure cells have been mounted at three levels in each silo to obtain the pattern of normal pressures around the wall. The first and the second level are close to the bin-hopper junction. At each level four positions spaced 90º apart are available for mounting the cells at. The third level is placed 1.8 m above the junction. Furthermore, a vertical distribution of cells along the silo wall has been set in the silo with concentric hopper.
In this study, the silo with concentric hopper has been instrumented with a total of 12 cells for measuring normal pressures along a vertical line of the silo wall. These cells consist of a system of strain gauges (Pople, 1979) mounted on a stainless steel clamped diaphragm. The interpretation of the initial results has covered several phenomena that frequently occur in this type of structures. They are: oscillations of the load from the stored material against the silo wall, unsymmetrical distribution of pressures around the silo wall, and patch-loads which are detected at different levels of the silo during the discharge process. A comparison has been carried out between the experimental results and the load model prescribed in a silo code (ENV 1991-4, 1995). The study of the observed phenomena will be further developed when results obtained from normal pressure cells mounted around the silo wall are available.
The obtained results contribute to the understanding of those phenomena that occur inside silos which is of importance for a more economic and safe design of silo structures.