Envelopes - From Influence Surfaces
Description
Envelope definitions may be automatically generated using Influence Surface Load Optimization from the Influence Surface Generation form.
They may be examined using the Define Envelopes form.
They create a special case of Enveloped Results.
Outline Procedure
Fully define the structure, so it is capable of analysis (but do not analyze it).
Open the Influence Surface Generation form (e.g. by using Data | Applied Loadings | Influence Surface... from the application Main Menu).
Envelopes will be generated automatically when (and only when) the influence surfaces for which load optimization is being carried out have been created for groups of members selected using Pick Modes: 'Beam-Longitundinal', 'Beam-Transverse' or 'Virtual member' AND when the picked member comprises more than one element.
Set View to 'Surface' and set Pick Mode to one of those noted above.
Pick members. Each single pick on a single member selects a series of member elements (typically running the full length or width of a bridge deck and being the equivalent of the overall length of a structural beam or deck slab). Multiple influence surfaces are thereby defined as a series of rows is created in the Influence Surface Generation form for each single pick. An influence surface is defined for every joint along the series of member elements. All rows in the series are defined for the same effect (rows differing only by member reference and end/node).
Influence surfaces should now be generated by picking Analyze in the Influence Surface Generation form.
Optimum (i.e. most severe) loading patterns should now be calculated by picking Run Optimization in the Influence Surface Generation form followed by definition of loading requirements in the appropriate Live Load Optimization form followed by Compile Loading Patterns.
In the course of the calculations (after the optimum loading compilation for every influence surface has been calculated) the effect is calculated of applying each optimum loading compilation on the influence surfaces of all rows in the series of rows that has been generated by the same single pick. At each joint (i.e. row) in the series the effects of all the load compilations for the series are compared and the most critical effect is derived. An envelope is then automatically defined. It contains only those compilations that create a critical effect in any of the rows in the series.
At the end of load optimization the number of compilations and envelopes that have been automatically created is displayed in the message window.
It is not essential to examine envelopes in the Define Envelopes form. (This stage is included here only for information)
Open the Define Envelopes form. (e.g. by using Calculate | Envelopes from the Main Menu).
The upper table lists (in addition to any previously defined envelopes) a Single Effect envelope for every series of members that has been selected by a single pick. The lower table for each single effect envelope contains Selected Cases Only and lists only compilations that are critical when analyzing all the optimum loading compilations for the series of members defined by a single pick. (Critical compilations are those that create a result on the bounds of the envelope of results for the given single effect).
If one or more members of Property Sets have been picked when creating series of influence surfaces (for example if the bridge comprises several identical parallel beams and each of the beams was picked) then a Property Set envelopes will also have been created. There will be one Property Set envelope for each Property Set that has a picked member.
The structure should now be analyzed (e.g. by using Calculate | Analyze from the application Main Menu) if it has not already been analyzed.
Open the Tabular Results form ( File | Results from the Main Menu).
In the Result Controller select Result Type: 'Envelope'.
Select one of the Single Effect envelopes. The left hand side of the displayed table lists stations defined by the reference number of every member in the structure (provided there is no filter). One of the two columns highlighted in yellow lists the critical result at each station for the effect originally selected when the influence surfaces were defined. The other lists the specific optimum loading compilation whose results created the critical result at each station. The associated results in other columns in each row are effects that occur concurrently with the critical effect. The displayed results for the series of members selected by the original pick are (in effect) the data (for the given effect) required to design a single beam incorporating that series of members sufficient to carry the design loading imposed by the code for which the optimum loading compilations have been derived.
Select the Property Set envelope. The left hand side of the displayed table lists stations at defined proportions of the overall length of the picked members. One of the two columns highlighted yellow lists the critical result at each station for the effect defined for that column. The other lists the specific optimum loading compilation whose results created the critical result at each station. By clicking the left mouse button with the cursor over any other column the effect for which the critical result is calculated may be changed. The associated results in other columns are effects that occur concurrently with the critical effect in each row. The displayed results along the series of proportions are (in effect) the data (for the given effect) required to for a design capable of carrying the optimum loading compilations on any member of this Property Set that has been selected by any of the original picks.
Differences between the Envelope Types are described in Tabular Results - Envelopes.