Pressures and deformations of bunker silo walls

Abstract

To investigate the structural stability of horizontal silo walls, a silo (length, 27 m; width, 9.1 m) with straight panels (length, 3 m; thickness, 0.16 m; height above the floor, 2.05 m) on one side and L-shaped wall panels (length, 4 m; thickness, 0.15 m at the bottom to 0.10 m at the top; height above the foot, 1.85 m) on the other side was constructed on the experimental farm of Ghent University. Displacement, strain and pressure measurements were performed during and after filling the silo with chopped maize. The displacements of the straight and L-shaped wall panels, measured with dial gauges and linear variable displacement transducers, were much higher than those predicted from published load combinations. The maximum measured displacements were 3.5 and 13.1 mm, respectively, for the straight and L-shaped wall panels. Moreover, in contrast with the assumption of perfectly restrained panels, the measurements showed that the panels acted partially like cantilever members. Strains were measured with mechanical deformeters, fibre Bragg grating sensors and strain gauges. The majority of both displacement and strain occurred during the second half of the filling process. When full, maximum strains on the outer surface of the silo wall of −110×10 −6 [dimensionless] and −220×10 −6 [dimensionless] were measured at the lower end of the straight panel and at the lower end of the L-shaped wall panel, respectively. The influence on the displacement as well as on the strain measurements of the presence of a surcharge load acting on the silage was very small. Nevertheless, short but high pressures were registered by the load cells when a surcharge load caused by a tractor and wagon passed near the measurement panel. Beneath a filling height of 1.2 m, the load cells indicated a triangular pressure distribution. For a half-filled silo, the simplified shape of the pressure profile is a triangle with a value at the base of 9.6 h  kN/m 2 , h being the filling height in m. For filling heights higher than 1.2 m, a peak value appeared at a height of 1.1 m. Beneath this height, the pressure decreased. A peak value of 23.5 kN/m 2 was measured for a completely filled silo.