5.2 Actions

When using the latest standards, such as EN 1990 or ASCE 7-16, it is often time-consuming to consider all eligible load situations and to select the decisive situations for the designs. In the Model - General Data dialog box, you can automatically create the combinations (see Figure 12.23).

The load cases defined in Table 2.1 (see previous Chapter 5.1) represent the base data for the automatic superpositioning. RFEM distinguishes between two load case categories: standard load cases and load cases of the type Imperfection. Moreover, for combining load cases, it is important to know, which action category the standard load cases have been organized into.

Standards provide rules for the combination of independent actions in various design situations. Actions are independent of each other if they arise from different origins and if the correlation between them may be neglected with regard to the reliability of the structural system.

In accordance with this concept, Actions to which load cases are assigned must be defined for the automatic superposition in RFEM. The action type defined for the load cases (see Chapter 5.1) controls the assignment to action categories in accordance with the standard.

The actions are already created when you define load cases. They are numbered consecutively. The sequence is not important but, if necessary, it can be modified by means of the [Renumber] button available in the dialog box.

In the table, you can add actions manually in order to, for example, assign load cases by user-defined specifications when huge models are designed.

The description of the action is derived from the action type that has been selected for the load cases. The preset description can be changed, if necessary.

The standards mention different action categories that control the partial safety factors and combination coefficients (see Chapter 5.1).

The list in the dialog box and table only provides the categories that were used for the definition of the individual load cases. Therefore, in order to create a new category, a new action type must be assigned in the general data of a load case.

Two or more load cases can be defined as acting Simultaneously, Alternatively, or Differently. The following example serves to illustrate the differences between these three options:

Table 5.1

LC1	Action A1	Action category "Permanent"
LC2, LC3, LC4	Action A2	Action category "3.A Imposed"

Depending on the definition of the Action A2, different possible combinations arise.

All load cases of the action can be combined as required. It is also possible to use them simultaneously in a combination. The following load combinations are generated in the example:

Table 5.1

CO1:	1.35LC1
CO2:	1.35LC1 + 1.50LC2
CO3:	1.35LC1 + 1.50LC2 + 1.50LC3
CO4:	1.35LC1 + 1.50LC2 + 1.50LC3 + 1.50LC4
CO5:	1.35LC1 + 1.50LC2 + 1.50LC4
CO6:	1.35LC1 + 1.50LC3
CO7:	1.35LC1 + 1.50LC3 + 1.50LC4
CO8:	1.35LC1 + 1.50LC4

Only one of the load cases of the action can be effective (e.g. wind from different directions). The following load combinations are generated in the example:

Table 5.1

CO1:	1.35LC1
CO3:	1.35LC1 + 1.50LC3
CO2:	1.35LC1 + 1.50LC2
CO4:	1.35LC1 + 1.50LC4

You can define detailed relations between the load cases of an action. If you select this option, an additional column appears in the Load Cases in Action dialog section. There you can assign load cases to a Group so that they are mutually exclusive (as is the case for the action Alternatively). You can select the number of the group from the list.

If you define LC2 and LC3 as a group in the example, the following load combinations are generated:

Table 5.1

CO1:	1.35LC1
CO2:	1.35LC1 + 1.50LC2
CO3:	1.35LC1 + 1.50LC2 + 1.50LC4
CO4:	1.35LC1 + 1.50LC3
CO5:	1.35LC1 + 1.50LC3 + 1.50LC4
CO6:	1.35LC1 + 1.50LC4

Load cases are assigned according to the specifications of the LC action type, so assignment is largely automatic.

To remove a load case from an action, select the load case in the Load Cases in Action column of the dialog box. Use the button or double-click the entry to transfer it to the Unassigned Load Cases dialog section. You can also set a load case inactive in the table: Select the empty entry in the list of the relevant table cell.

Manually removed load cases are transferred to the Unassigned Load Cases list while considering the action type. This also means that only load cases of the same action type can be included in an action category. For example, it is not possible to select load cases of the type "Imposed" for actions of the type "Snow" – neither in the dialog box nor in the list of the table (see figure on the left). Type-different load cases are therefore not visible in the Existing Load Cases list. Use the [Show Unused] button to display load cases of other categories. They are shown as locked and cannot be selected.

Enter a user-defined note or select an entry from the list.

The buttons in the Actions tab of the Edit Load Cases and Combinations dialog box have the following functions:

Table 5.2 Buttons in the Actions tab

	Creates a new action.
	Renumbers the selected actions.
	Selects all actions.
	Cancels the selection in the list.
	Automatically assigns unassigned load cases to actions.
	Deletes the selected actions.