Structural loads on bunker silo walls: Experimental study

Abstract

An experiment to obtain wall pressures in a large bunker silo was carried out for 2 consecutive years. Normal wall pressures were measured with 18 pressure sensors mounted on a 3·7 m wide by 4·9 m high precast concrete wall panel of a 51 by 90 m bunker silo in Walker-ton, Ontario, Canada. The silo was filled with whole-plant corn silage both seasons. Wall pressures were measured during filling, during compaction with a 21 t bulldozer, and for about 3 months thereafter. Results from the 2-year experiment showed that the silage loading increases almost linearlywith depth measured from the silage surface. Thus, wall loading exerted by the silage can be expressed as a linear function of a pressure ratio and the silage density; the pressure ratio in this function would be the ratio of the normal wall pressure to the vertical stress in the silage. In the 1987 experiments, silage pressure was found to increase with depth at the rate of about 5·3 kPa/m and in the 1988 experiments at the rate of 6·8 kPa/m. The maximum pressure in 1988 was 28 kPa at the lowest sensor. In 1987, the top of the silage was flush with the top of the wall. In 1988, the silage was piled up well above the top of the wall with a surcharge angle of about 15°. The maximum values exceeded the 1983 Canadian Farm Building Code design load by afactor of 3·8 and 4·5 in 1987 and 1988, respectively. The maximum pressure in 1988 exceeded the new 1990 Canadian Farm Building Code by a factor of about 1·3. The maximum wall pressure due to the weight of the 21 t bulldozer used to compact thecorn was 10 kPa near the silage surface, 15% of the pressure under the tracks of the bulldozer.