AD.2007-03.1.3 Generation of Primary Load Cases Using Repeat Load Commands
With the large number of combinations that are required by design codes, STAAD.Pro introduced a tool to allow the combinations to be created automatically based on a rule set. This functionality has been enhanced to allow the automatic creation of equivalent combinations, but using primary load cases and the REPEAT command.
The use of the COMBINATION command to obtain results for a collection of load cases that occur together is entirely valid when using first order analysis and models that are not dependant upon the forces in them (such as tension only members or one-way supports). In these cases, the law of superposition allows the results of each load case to be multiplied by a scaling factor and added together. However, for models where this does not apply, such as using a P-DELTA analysis, TENSION ONLY members or ONE-WAY supports, then the law of superposition does not necessarily apply. For this reason, STAAD.Pro has the ability to create primary load cases which replicate the effect of a combination, but in a primary load case. This means that the analysis will solve the load case by using the applied loading rather than simply adding the results. This is achieved in a primary load case by using the REPEAT command.
For full details of the REPEAT command see TR.32.11 Repeat Load Specification.
By selecting the option Create Repeat Load Cases all the load case combinations in the Selected Load Combinations list will be created into primary load cases:
Note the difference in the Load & Definition dialog when comparing a generation of Combination load cases rather than Primary load cases with REPEAT commands: