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5.1 Load Cases
The loads from a particular action are stored in a load case (LC). Load cases can be, for example, self-weight, snow, or live load.
The loads in the load case should be defined as characteristic actions, which means without factors. The partial safety factors can be considered later when the load cases are superimposed in load or result combinations.
For each load case, you can separately define, which calculation method (linear static, second order, or large deformation analysis), approach, and calculation parameters (load increment factor, stiffness reduction by partial safety factor of material) you want to use.
There are several ways to open the dialog box for creating a new load case:
- The Insert → Loads Cases and Combinations → Load Case menu option
- The [New Load Case] button in the toolbar
- The shortcut menu of the Load Cases navigator entry
The Edit Load Cases and Combinations dialog box appears. A new load case is preset in the Load Cases dialog tab.
- It is also possible to enter a new load case in an empty row of Table 2.1 Load Cases.
The number of the new load case is preset but can be modified in the LC No. text box. If the entered number has already been assigned, RFEM displays a warning when you close the dialog box.
The creation of load cases should be well organized. Gaps in the numbering are allowed so that you can insert additional load cases later. The order of load cases can be changed retroactively with the [Renumber] dialog button (see Table 5.1 and Chapter 11.4.8).
You can enter any name manually. You can also choose a name from the list to briefly describe the load case.
The check box allows you to control if the load case is taken into account as an independent load case in the calculation. In this way, it is possible to exclude load cases from the calculation which do not occur in isolation (e.g. wind without considering self-weight) or whose results are not relevant for a preliminary design.
The standards mention different action categories that control the superposition of load cases, as well as the partial safety factors and combination coefficients. Each load case must be assigned to a category.
The list in the dialog box or table provides several categories for selection. They depend on the standard set in the Model - General Data dialog box (see Chapter 12.2.1).
These categories are significant for combining load cases manually or automatically. The classification of the load case determines, which factors are applied when creating load and result combinations.
If you want to take the construction's self-weight into account as a load, select the Active check box. The load's direction of action can be defined in one of the three text boxes by means of the self-weight factor. The default setting is 1.00 in the direction Z or -1.00 if the global axis Z points upwards.
If the automatic self-weight is applied in several load cases, you have to consider this for the combination of load cases.
Here you can enter a user-defined note or select an entry from the list to describe the load case in detail.
The Calculation Parameters tab in the Loading dialog box provides different options for controlling the calculation. You can find a detailed description of these parameters in Chapter 7.3.1.
There are several ways to change the general data of an existing load case:
- Menu option Edit → Load Cases and Combinations → Load Case - General Data
(current load case)
- Menu option Edit → Load Cases and Combinations → Load Cases
(selection from all load cases)
- Shortcut menu or double-click of a load case in the Data navigator
- The [Edit load cases and combinations] button in the toolbar of the loads tables (current load case).
In the Edit Load Cases and Combinations dialog box, there are several buttons available below the load case list (see Figure 5.3). The buttons have the following functions:
Creates a new load case.
Creates a new load case as a copy of the selected load case (see below).
If several load cases are selected, all contained loads are copied to a new load case (see below).
Assigns a new number to the selected load case. Specify the number in a separate dialog box. You may not enter a number that has already been assigned.
Selects all load cases.
Cancels the selection in the list.
Inverts selection of load cases.
Deletes the selected load case.
You can use existing load cases to create new ones.
To copy a load case, select the relevant load case in the Existing Load Cases list. By clicking the [Copy] button, you can create a copy of the load case with the next available number. You can subsequently adjust the description of the new load case and the loads.
When adding load cases, the loads of several load cases are copied into a new load case. First, select the relevant load cases in the Existing Load Cases list (multiple selection by holding down the [Ctrl] key). Then, use the [Add] button to copy the loads into a new load case.