Section Design situations

1)P The general format given in ENV 1991-1 for design procedures is applicable.

NOTE This does not mean that clauses and values specified for buildings in ENV 1991-1 may be applied to silos and tanks.

2)P Selected design situations shall be considered and critical load cases identified. For each critical load case the design values of the effects of actions in combination shall be determined.

3)P The combination rules depend on the verification under consideration and shall be identified in accordance with ENV 1991-1, "Basis of design" and in accordance with Annex A.

4) The arrangement of actions on silos and tanks for load cases in a particular design situation are indicated below.

5)P Prefabricated silos shall be designed for actions due to handling, transport and erection.

6) Loads arising from the maximum possible filling shall be considered.

7) Load patterns for filling and discharge can be used at the ultimate and serviceability limit states.

8) The following accidental actions and situations shall be considered where appropriate:

— actions due to explosions;

— actions due to vehicle impact;

— seismic actions;

— fire design situations.

9) Tanks and silos may be used to store liquids or particulate materials which may cause explosions. Some of the materials which may lead to dust explosions are listed in Table 7.1.

10) The potential damage from dust explosions should be limited or avoided by appropriate choice of one or more of the following:

— incorporating sufficient pressure relief area;

— designing the structure to resist the explosion pressure.

11) The explosion pressure in a silo without adequate relief area may be as high as 1N/mm2.

12) Prevention of dust explosions should be considered during design by appropriate choice of one or more of the following:

— prescribing proper maintenance and cleaning routines;

— avoiding ignition by the safe selection of electronic equipment;

— careful use of welding equipment.

13) Cracking shall be limited to prevent water penetration when designing silos for water sensitive materials at the serviceability limit state.

14) The effects of fatigue shall be considered in silos or tanks that are subjected to an average of more than one load cycle a day. One load cycle is equal to a single filling and emptying. The effects of fatigue shall also be considered in silos affected by vibrating machinery.

15)P The actions from adjoining structures shall be considered.

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