## 5 International Standards and Solid-Induced Design Loads
### Loads Evaluation Philosophy According European Standards EN 1991-4:2006  
Generally, three main factors must be considered to estimate the loads exerted on silo walls: the silo geometry, the stored material properties, and the discharge flow pattern. Since the pressure applied on the silo wall differs depending on the stored material situation (flowing or stationary) and on its flowing pattern, the assumption of a uniform distribution around the perimeter of the bin is one of the most common design errors causing failures [70]. As a matter of fact, an increment of the uniform pressure may be imposed to cover the discharging and unsymmetrical actions caused by eccentric filling/discharging [71]. Generally, the loads imposed by the stored material on silos could be classified as horizontal wall load, wall frictional pressure, patch loads, hopper loads, and kick loads. This section addresses solids-exerted loads on the silo walls. These loads could be symmetric or asymmetric, either distributed or patch loads and they are represented according to the different standards. For instance, according to EN 1991-4 and depending on the action assessment classes of the silo and its geometry, the loads imposed by the stored material on the vertical silo wall could be calculated. These loads are generally classified into two main categories: (a) filling loads; (b) discharge loads. The design may depend solely on the filling loads, only if the internal pipe flow is guaranteed. However, the filling loads are represented by a uniform symmetric pressure, which is a static pressure subdivided into horizontal and frictional traction induced by the stored material and affected by several factors, as the silo geometry, material properties, and the wall-material interaction coefficient. In addition to the symmetric filling pressures, filling patch loads, expressed in terms of localized horizontal loads, should be considered without an associated frictional traction. Patch loads are considered to account for unsymmetrical pressures caused by a possible eccentric pile of filling, especially in the case of small eccentricities. On the other side, unsymmetrical distribution of the horizontal pressure should be considered in case of large eccentricities. Similarly, discharge loads are represented by a uniform symmetric distributed pressure in combination with patch loads. The uniform discharge pressure can be considered by increasing the uniform filling pressure using discharge magnifying factors, in order to account for the increase in both the horizontal and frictional pressure. Discharging patch loads can be considered in a pattern of only normal pressure (no frictional traction) to account for the accidental asymmetry of loading during discharge in case of small eccentricities, while the unsymmetrical horizontal pressure on the wallshould be accounted in case of large discharging eccentricities. Patch filling/discharging loads may be ignored for silos in action assessment class 1, while a uniform increasing in the symmetrical pressure may be used when considering special structural arrangements to substitute these loads in the action assessment class 2. When large eccentricities are expected, as large outlet eccentricity or large filling eccentricity with high slenderness, a special procedure must be followed to account for the unsymmetrical wall pressure distribution resulted by the eccentric pipe flow channel. In the end, the loads on the vertical walls could be expressed in terms of symmetrical loads, due to filling and discharge that include horizontal pressure and frictional traction. In addition, the unsymmetrical loads caused by filling/discharging eccentricities should be represented either by considering patch loads for small eccentricities, or by considering unsymmetrical pressure (horizontal pressure, defined as \(p_{h}\), and wall frictional traction, defined as \(p_{w}\)) for larger eccentricities, depending on the action assessment class of the silo.