Some experts users have detected that the calculation of concomitant values on an earthquake analysis was not possible in generation 5 but it is now.
In earthquake calculations, due to the existence of the overlapping rules, finding a maximum value is really easy, but finding concomitant values is not. Why is this? With the CQC/SRSS rules, the value of an specific component, for example, Mz, comes from a square root, so the results are absolute values without a sign. How are the maximum and the minimum calculated from there? For every type of results (reactions, moments, etc) we only have the absolute value ABS, so the minimum is fairly easy (=-ABS) and the maximum (=ABS); but what about the concomitant values.
Thus, in STATIK-5 we simply gave the maximum and the minimum values for each component, but we could not really give the concomitant values.
For the design envelopes all we could do was to sum each maximum and minimum couples in a component:
[S1] = My max, Mz, Nx
[S2] = My mín, Mz, Nx
The 8 sign combinations Mya, Mza and Nxa (with the values obtained from the spectral analysis), that is, +++ ++- +-+ +-- -++ -+- --+ ---
From there come the 48 load cases that were studied at each section (if we did the 3 envelopes).
In STATIK 7 we use an approximation which is different from the earthquake results and we now can manage each component separately and find the corresponding concomitant values.
As it can be seen on page C-12 of the STATIK-7 manual, as it is impossible to obtain concomitant values, a series of simplifying assumptions is necessary. We use the approach suggested by C.Katz on this document: http://www.sgeb.ch/dach_mitteilungsblatt/DACH_Mitteilungsblatt_09_3.pdf from page S-14 onwards, although it is in German, the response spectrum overlapping can be seen...
The following images show why it was not possible to obtain the concomitant values and now it is:
These images are also available in the attached PDF: