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g is the weight density ^ is the wall friction coefficient Ks is the horizontal/vertical pressure ratio z is the depth U is the internal perimeter 2)P The resulting vertical force in the wall pw (z) per unit length of perimeter acting at any depth z is:

3) Methods for determining the particulate material properties weight density, the wall friction and the pressure ratio are given in section 5.7. Vertical walled section

1) The filling load is composed of a fixed load and a free load, called a patch load.

2)P The fixed load shall be calculated from expressions (5.2) and (5.3).

3) The patch pressure Pp shall be considered to act on any part of the silo wall and is taken as:



el and dc are shown in Figure 1.2.

4) For concrete silos, silos with stiffeners and silos with non circular cross-section shapes, the patch pressure shall be taken to act on two opposite square areas with side length s (Figure 5.2), equal to:

5) In many silos a simplified approach can be used to apply the patch load. The most unfavourable load arrangement can be designed for by applying the patch at the mid-height of the silo and using the percentage increase in the wall stresses at that level to increase the wall stresses throughout the silo.

6) For thin walled circular silos the patch pressure shall be taken to act over a height s, but to extend from a maximum outward pressure on one side of pp to an inward pressure pp on the opposite side (Figure 5.2). The variation shall be taken as:


6 is given in Figure 5.2.

7) The total horizontal force Fp due to the patch load on unstiffened steel silos is given by:

8) A simplified method can be used for applying the patch load to thin walled circular silos. The patch load may be taken to act at a depth zo below the equivalent surface, or at the mid-height of the vertical walled section, whichever gives the higher position of the load.

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