Introduction to load case combinations

Load cases defined in the project can be combined in load case combinations. The combinations can be then used for evaluation of results and for checking to national codes.

Combinations may be of various types. Each type is used for different checks. However, all the types can be used for an initial evaluation of results (i.e. reviewing of calculated internal forces).

SCIA Engineer allows the user to use three different types of combination: linear, used, code-related. The linear combination as the simplest one is not important for the following reasoning.

But when either user or code-related combination is used, there are two critical points:

the user uses the combination as a "black box"	The user just trusts the program and cannot see nor evaluate what goes on "behind the scenes".
the user explodes the combination into all possible combinations	The user can see and evaluate all the linear combinations created from the selected set of load cases included into the combination. But the number of these combinations may be enormous and usually leaving the user confused and the final checking uncertain, notwithstanding the deteriorated speed of the program response.

The new solution is based on dynamically created list of "dangerous" combinations.

For example, in the example given later just 7 "dangerous" envelopes are created. This is a very sensible number in comparison with the total number of 164 possible linear combinations that may be created for the same example.

There are two approaches for the treatment of the "dangerous" combinations.

background use	The combinations are created on the background and the user is not disturbed at all.
foreground use	The user may decide to explode the defined combination and see the "dangerous" combinations.

Note 1: Regardless of the approach selected, the numerical results will be the same, as for both approaches the calculations are performed for the same combinations.

Note 2: In addition, if there a special need arises, the user still has the choice to explode the defined combination into all the possible linear combinations that may be then evaluated one by one.

Advanced load case combinations

We use the term "advanced" combination for a combination that is designed for other than static linear combination. They treated separately in appropriate chapter of the book.

Note: A nonlinear combination MUST be defined if the user wants to perform nonlinear calculation. A stability combination MUST be defined if the user wants to run a buckling analysis. If such a combination (nonlinear or stability one) has not been input, the corresponding calculation is NOT even available in the Calculation dialogue.