Collapse of the Fargo Grain Elevator
One of the most dramatic bearing capacity failures was Fargo Grain Elevator collapse of
1955. This grain elevator was built near Fargo, North Dakota, in 1954. It was a reinforced
concrete structure composed of twenty cylindrical bins and other appurtenant structures,
all supported on a 15.8m (52ft) wide, 66.4 m (218ft) long, 0.71 m (2ft 4in) thick mat
foundation.
The average net bearing pressure, q’=q-’z0 = 76.1 kPa ((1590 lb/ft2), caused by the weight
of the empty structure was 76.2 kPa. When the bins began to be filled with grain in April
1955, q’ began to rise, as shown in Fig. 2 below. In this type of structure, the live load (i.e.
the grain) is much larger than the dead load; so by mid-June, the average net bearing
pressure had tripled and reached 227 kPa (4,750 lb/ft2). Unfortunately, as the bearing
pressure rose, the elevator began to settle at an accelerating rate, as shown in Fig. 3.
Early in the morning of June 12, 1955, the elevator collapsed and was completely
destroyed. This failure was accompanied by the formation of a 2 m bulge as shown in Fig.
4.
Conduct a bearing capacity analysis on the Fargo Grain Elevator and back calculate the
average undrained shear strength of the soil. The groundwater table is at a depth of
1.83m below the ground surface. Soil Strata A and B have unit weight of 17.3 kN/m3;
stratum D has 14.9 kN/m3. The unit weight of stratum C is unknown. Assume that the load
on the foundation acted through the centroid of the mat.
Fig. 1 Elevation views of the elevator.
Fig. 2 Rate of loading
Fig. 3 Settlement at centroid of mat.
Fig. 4 Cross section of collapsed elevator.
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