Design criteria for structural design of silage silo walls

• For silo wall height of 4 m, the design juice level was exceeded in 21% of cases.
• Silage juice from hydrostatic pressure and saturated silage did not act as free water.
• Silage juice increased more than 24% in 6 out of 10 silos 4 months after filling.
• The new load model distinguishes the load variation over time more precisely.
• The data indicated a need to determine the ULS for filling and utility period.

Existing Swedish design guidelines (JBR) cover silo wall heights up to about 3 m. These guidelines presumably overestimate the forces and pressures exerted by silage juice when silo walls are more than 3 m high, which could result in over-sizing, material waste and increased capital costs. This study determined silage physical properties in terms of horizontal wall pressure and evaluated silage juice levels in silos with a wall height of 3 m or more.Wall pressure was measured by transducers mounted on a steel ladder rack placed vertically along the internal silo wall. The ladder rack also permitted measurement of silage juice levels in slotted steel pipes. The pressure on the transducers was recorded by a data acquisition system displaying static and total loads (pressures imposed by silage material without and with the compaction machine, respectively).The static pressure at the bottom of the silo wall (4 m) was 16 kPa during filling and compaction, and 22 kPa 1–4 months after filling. The silage juice did not interact with compaction. The wall pressure increased by 30% after filling, but the increase was only significant at 1 m from the silo bottom. The dynamic load was 17 kPa when the compaction machine passed 0.1 m from the silo wall.New guidelines are proposed based on the results and on the Eurocode for ultimate limit states (ULS) for two stages; filling and the utility period. The design bending moment for ULS was 21% lower than specified in JBR.