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Combining cases

It is often useful to combine results from more than one analysis case, by defining combination cases.

Simple combinations​

A simple combination case is made up of a number of factored analysis cases. For example, if Analysis case 1 relates to dead load and Analysis case 4 to wind load, then the combination case might be:

1.4𝐴1 + 1.2𝐴4

Note: Combinations are only valid for linear solutions and should not be used to combine results from nonlinear analyses.

They are similar to analysis cases but differ in some respects:

  1. Results for combination cases are inferred from analysis case results, and not calculated explicitly.

  2. Syntax is based on analysis cases, rather than load cases. See Syntax of combination case descriptions for more information on how to specify combinations.

Enveloping combinations​

You can envelope most results produced in GSA. A result envelope is the worst (maximum and minimum) results encountered in a series of analysis or combination cases.

An enveloping combination is a number of permutations of simpler combinations. During the enveloping process, GSA compares the results for each of these simple combinations to arrive at the envelope. The permutations for each envelope can be viewed under Explorer pane > Output > Case permutation factors.

Outputs of envelopes may be either:

  • All components listed

Or

  • A defined subject component reported alongside coexistent values for other components

For example, enveloping on MyyMyy will show the associated axial and shear values.

Note: Where different components being enveloped in a table are related, and where a direction and magnitude varies between cases - e.g., resolved forces and displacements - the relationship between the components will not be satisfied with values from different permutations.

See the Tutorial or References for guidance on how to define envelopes.

Enveloped results can also be displayed in Graphic views. Some examples of what can be displayed are listed below:

  • The maximum and minimum deformed shape can be drawn.
  • The maximum and minimum diagram can be drawn, with an option to annotate just the maximum, minimum or both.
  • Either the maximum, minimum, absolute, or signed absolute value can be contoured.

Note: If you request a diagram of 2D element derived stresses, GSA will plot the most positive Max / Min stresses at the most positive angle, and the most negative Max / Min stresses at the most negative angle. An angle from a different permutation to the Max and Min stresses is not an accurate representation of the state of stress.