|
||
|
|
||
A project contains some static load cases and one or more seismic load cases.
A linear combination is created, which contains one or more seismic load cases. This can be done either manually or by exploding an envelope or a code-defined combination.
When looking at results for that combination, internal forces for instance, although the combination is linear, envelope results are displayed. The combination key clearly shows, that envelope results are generated, alternating the sign of load case coefficients for all seismic load cases.
As shown above, the simple fact, that the combination key shows 4 combinations instead of a single one indicates that the defined linear combination is handled as an envelope. The coefficients for all static load cases are the same for all combinations in the combination key. The sign of coefficients for seismic load cases (LC4, LC4_AE, LC6 and LC6_AE) changes in each combination.
The reason for that behavior is, that all seismic load cases in this project are defined as unsigned seismic load cases.
Because of that, each seismic load case in itself is considered as an envelope and, although the containing combination is defined as linear, the final result is an envelope.
As a general rule, do not use unsigned seismic load cases in linear combinations. See "Combinations containing seismic load cases".