Working with Envelopes

Envelopes are useful for keeping track of maximum and minimum values resulting from multiple load combinations, moving loads, and so on. Essentially, envelopes are auxiliary plots that record the maximum and minimum values that occur along each member. The example below shows the moment envelope resulting from moving the 25 k point load across the top of the frame:

With default settings, the overall maximum and minimum values for the frame will be automatically labeled in red as shown above.

Most of Dr. Frame's plotting is "smart", e.g., moment diagrams that can be represented by two straight lines are plotted as such, and maxima and minima are captured precisely. Due to the nature of envelopes, though, envelope plotting occurs on a fixed grid for each member. As a result, envelopes do not offer quite the same precision as regular plots.

Controlling Envelope Calculation and Display

All else being equal, calculating and displaying envelopes can be relatively expensive in terms of computations required and screen clutter introduced. For this reason, the Envelopes menu provides various options for managing envelope calculation and display:

Enable/Disable Calculation commences/halts the calculation and storage of plotted maxima and minima, but envelopes are not displayed.
Show/Hide Envelopes displays/hides the envelopes in their current state. If calculations have not been previously enabled, then Show Envelopes will enable calculation, as well as turning on their display.
Reset All Envelopes removes all envelope history, and envelope calculation re-commences from the current state.

Using the cursor keys to move loads can help to produce smooth envelopes.

The menu commands will be applied either to the entire frame if there is no selection, or to whatever members/sets of members are currently selected.

Envelope data currently are not stored with files or undo states, so they must be regenerated after opening a file.

Controlling Envelope Labeling

Automatic envelope labeling is controlled by the same commands used to control labeling of regular plots. Thus, the commands in the Options>Automatic Labels popup can be applied in the same manner as was discussed earlier for Plot Labels.

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