How to create nonlinear combinations using “new from combination”?
In SCIA Engineer nonlinear combinations are needed when performing a nonlinear calculation. This can be done via Main > Load cases, Combinations > Nonlinear combinations. In this window you have the option “New from combination” on the bottom left corner. This is a useful tool to help you generate nonlinear combinations. The only requirement is that there should be a linear combination available. This can be done automatically for EC-EN combinations.
When clicking “New from combination” you are asked to select the type of combination. This can be Linear or Envelope. The automatic generated combinations are Envelope combinations. Hence, there are no available combinations for the Linear type in this example. To use the Linear type of combination, the automatic generated combinations must be first Exploded to linear. The user can of course also input self-made linear combinations which will then be available for the type Linear.
When selecting the ULS-Set B (auto) combination and the filter put on All, you can see the estimation of to be generated nonlinear combinations as well as the option to put them all in a new result class.
If the number of potential nonlinear is significantly high (>100) a warning will appear stating that it can take a long time to generate all nonlinear combinations.
After confirming with OK, the generated nonlinear combinations will appear and can now be used for the nonlinear calculation.
All dangerous filter
To control the number of generated nonlinear combination a filter can be used. The filter can be put on All (see above) – All dangerous – Most dangerous. A dangerous combination is one that creates an extreme effect in some member in the structure. That extreme effect can be an internal force or stresses in the extreme fibers of the section. Linear results will be used in order to estimate which members are getting these extreme effects. The result will be a lower amount of nonlinear combinations because not every linear combination can be considered dangerous.
Most dangerous filter
The last option is to put the filter on Most dangerous. Here can be specified how many dangerous combinations are considered. This can be useful when the user wants to run a quick analysis with a lower amount of dangerous combinations. However, the safer option is to use the filter for All dangerous combinations since here more combinations are considered.