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differences between load groups and load combinations

In RSTAB RFEM and there has always been two ways to superimpose Lastlälle. There are load combinations and load groups. In both one can define superposition rules for load cases. The question is, what exactly are load combinations and how to load groups calculated.
If a load combination is formed, then the first place, it contains load case passed to the solver and calculates the results. Then the results are superimposed. In
load groups, it is something different. First, the loads are grouped according to the superposition rule. Which is then passed to the calculation engine, which then determines the results. meets

superposition of the loads
calculation
what has been said on all versions of RSTAB and RFEM:

Again the sequence in load combinations:

1. calculation of load cases
2. overlay

And load groups to. In the course of development, treatment was changed somewhat.

differences between versions

In RSTAB 5 was principally to avoid the load groups are always expected to second-order theory. Setting did not exist. If you wanted to calculate first-order theory, then had to load combinations are used. From
RSTAB RFEM 6 and 1, was different. From these versions could be set according to which theory of load cases and load groups should be calculated. It is now easily possible to load groups to be calculated by first-order theory. But for what? When

group when using combination?

load combinations are actually a convenient Thing. Example: LF1
is dead weight, wind from right LF2 and LF3 wind from the left. One could now so define a load combination:

• LK1: LF1 / LF2 or LF3 + S

It can therefore be studied in a load combination of wind and wind right from the left by means of a so-called OR-combination. This is for RSTAB no problem, since only the results are superimposed.
When load groups not possible, the loads are superimposed. This can not be decided from the outset, which lead to minimum and maximum loads. Therefore, for the above case would have two load groups are defined:

• LG1: LF1 + LF2
• LG2: LF1 + LF3

load groups do so for the first time more work. But they also have advantages. Once the system is not linear, then results may not be superimposed. For nonlinear systems is no longer the superposition law. You may work in this case not so with load combinations. But when a system is not linear? Three cases are distinguished:

1. Geometric nonlinearity
2. structural nonlinearity
3. Physical nonlinearity

Geometric Nonlinearity: This is the calculation according to theory, II and III. Order and the post-critical analysis meant. Once you can no longer expect to first-order theory, then load groups are necessary. This is nothing new. But why do I load groups according to the theory right?
structural nonlinearities: these include, for example, non-linear bar elements. The tension rods are, for example. Such nonlinear elements can the structural system of load change to load case. Example:

Structural system for load case 1

Static system must load the Case 2

results from different static systems of course not be superimposed. This applies in RFEM The following Nichtliniearitäten:

• staff nonlinearities
• loss in train
• loss in pressure
• tearing
• flow
• plastic hinges
• slip
• tension bar
• strut
• buckling
• nonlinear bearing
• Flächenbettung with failure to train or pressure
• Nonlinear linear bearing
• Nichtliniare storage node contact elements

If such elements in the file before, then load combinations can lead to false results. Therefore, the program is also a warning issued.
There are some background information needed to load groups and load combinations to best effect.