# Steel Connection Design – What are the filtering criteria for envelopes and how to use them?

All connections available in the Steel Connection module can be designed using all combinations or envelopes created from those combinations.

The possibility to choose how to use the combinations in the design process is available in the Design Assumptions dialog.

By selecting Envelopes method, the calculation will be performed using only the combinations that provide Max/Min of the design forces using certain filtering criteria done in Advance Design Steel connection.

The envelopes that are considered now in calculation can be seen inside the new Combinations report or inside detailed or intermediate reports in the Load combinations chapter.

The Combinations report added to the available report list for each joint type will display only the Load combinations description chapter, which will provide an easier and faster way to access the envelope list.

As have been mentioned, there are two options possible: All and Envelopes.

Now let’s see how the selection affects the behavior during calculation process.

Combinations = All

For Combinations set on “All”, the Advance Design Steel Connection is using all the combinations generated to design the connection.

Example:

For the Base Plate connection for a tubular column as on the picture below, the number of combinations is 181, and all are used for design calculations. It influences the report (as a table listing all the combinations is long), but the most important is that due to the number of combinations, the calculation time is relatively long.

Combinations = Envelopes

For Combinations set as “Envelopes” the module will calculate the connection using just some of the combinations which are fulfilling certain criteria.

The criteria used to select just a part of the combinations are the following:

Based on these criteria, Advance Design Steel Connection module is selecting the combinations that compliant with one or more criteria and does the design calculations based on the selected combinations.

The calculation time decreases, and the report is much more compact as only the selected combinations will be listed.

Example:

For the Base Plate connection for a tubular column as on the picture below (having more load cases that the previous example), the number of combinations is 482. But this time calculations are done with “Envelopes” of combinations.

Even there are 482 combinations, thanks to the envelopes, the calculation time is less than for the previous example. And in addition, the report does not have pages full of combination tables and it is generated much faster. The Load combinations description table on the report contains now only several combinations that are fulfilling one or more criteria. And the connection is verified using these combinations