Enveloped Results Overview
Requires: Advanced Level
The enveloped results feature is just as it sounds: It is a way to view demands of various load cases in a single overall "Result Case". Any envelope case actually consists of two sets of results, the minimum and maximum values, these are referred to as "Lower Extremes" and "Upper Extremes".
You do not necessarily need to use this 'Envelope' feature to find extreme results! Reports can help you locate extremes and design-checks do it automatically! This 'advanced' feature allows extremes to be calculated and stored for time-history results, moving load and superposition combinations.
Using Enveloped Results
By default, Envelope Results are not enabled. To enable Envelopes, find the "Calculate Envelopes?" option in the Project Settings settings on the Modify Tab of Project Manager. This feature may also be enabled with a check box in the Load Case Manager on the Advanced tab.
Types of Envelopes
These are the types available, not all will be created in any given project, it depends on what other load cases or load types you have.
- ASD Envelope: Any load combination designated for service-level design checks.
- LRFD Envelope: Any load combination designated for strength-level design checks.
- LRFD Overstrength Envelope: Any load combination designated for strength design and with the seismic overstrength option turned on.
- Serviceability Envelope: Any load combination designated for deflection checks.
- All Envelope: Everything. Any load case or combination, dynamic results, moving loads, etc.
Viewing and Reporting the Envelopes
As mentioned above, the process to obtain an envelope is essentially automatic. To view the resulting envelope there are a couple of options. Just like other load cases or combinations, the Envelope Results show up on in a Result View. Use the Command Bar at the top of the Result View to select one of the Envelope Cases to display.On the Filter Tab of the Project Manager under the Results Display heading use Envelope Type to control which set of results "Low Extreme" or "High Extreme" to display. Note that these are the upper and lower extremes and it is very possible for your largest moment to be negative and occur in the minimums case.
Envelope Moment Diagrams
The first option for viewing the envelope is graphically. As with other load cases you can select a member, then right-click and choose Graph Member from the context menu. This will typically default to a plot of the deflection, shear, and bending moment for the member but can be customized to include or exclude items. The Member Graph shows both the maximum (High Extreme) and minimum (Low Extreme) for the envelope. The Low Extreme is defined by the boundary with a lower magnitude while the High Extreme forms the boundary with the higher magnitude (absolute value). Viewing the results of a simple cantilever beam and comparing them to the Member graph will help clarify exactly what is being displayed. You may notice that the plots typically have sharp changes or steps in them usually indicating where a different load case has begun to control.
The other way to view the resulting envelope is with typical reports. The reports are very similar to member reports in other load cases. You can view Member Internal Forces, Local Displacements, and other items. As usual you have the option of viewing just the extreme results (i.e. the extreme results of the envelope) or you can view a detailed table of all the results along an element.
Note: Envelope results are calculated at discrete places along the length of the member. The high and low extreme values at each location may come from completely different load cases, therefore VisualAnalysis will not linearly interpolate between the result-locations to produce a "summary" report, or a report showing more or fewer offsets than were calculated internally.. The moment diagrams are not smoothed and you may see jumps or spikes in the values that for normal results you would not expect to see! To control the number of places where envelope results are calculated, set the values into some upper limit.