Sum of reactions and sum of forces for CQC/SRSS quadratic combinations

[faisal.aaouatif]

Good Morning / Evening

1.from the RSA Help it is stated that :

"In quadratic combinations for cases of the seismic or spectral analysis, the sum of reactions and the sum of forces are calculated by adding the values of the respective sum of values and the sum of forces for individual vibration modes"

Can we have a little more explanation ie : the somme of reactions are equal to ....

and the somme of forces are to....

2.When using Reaction table; Values of shear force at the base of a building are those on columns corresponding to the "somme of reaction" record [ and not those on somme of values ]

Help appreciated.

@faisal.aaouatif Artur Kosakowski edited the topic for better findability and marked post as the solution. If it did not work as an answer, please post your reply in this thread so that I can unmark the solution. 

[faisal.aaouatif]

Good Morning / Evening

1.from the RSA Help it is stated that :

"In quadratic combinations for cases of the seismic or spectral analysis, the sum of reactions and the sum of forces are calculated by adding the values of the respective sum of values and the sum of forces for individual vibration modes"

Can we have a little more explanation ie : the somme of reactions are equal to ....

and the somme of forces are to....

2.When using Reaction table; Values of shear force at the base of a building are those on columns corresponding to the "somme of reaction" record [ and not those on somme of values ]

Help appreciated.

@faisal.aaouatif Artur Kosakowski edited the topic for better findability and marked post as the solution. If it did not work as an answer, please post your reply in this thread so that I can unmark the solution. 

[Pawel.Pulak · Accepted solution]

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@faisal.aaouatif wrote:

1.from the RSA Help it is stated that :

"In quadratic combinations for cases of the seismic or spectral analysis, the sum of reactions and the sum of forces are calculated by adding the values of the respective sum of values and the sum of forces for individual vibration modes"

Can we have a little more explanation ie : the somme of reactions are equal to ....

and the somme of forces are to....

---

It was discussed by me in the message 2 of this forum topic:
http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Seismic-Result/td-p/3101884
and in the message 4 of this forum topic:
http://forums.autodesk.com/t5/Autodesk-Robot-Structural/design-one-spread-footing-with-three-columns...

Recapitulating it in case of CQC combination for seismic or spectral load case :

the sum of reactions ("Sum of reac.") is calculated in the following way:

a/ first for each vibration mode the sum of reactions ("Sum of reac.") is calculated by adding (linear combination) reactions from all supports (including reactions from bar and panel elastic foundations providing they exist - which are not shown in the table of reactions)

b/ then the sum of reactions for CQC combination is calculated as the CQC combination from the sums of reactions for individual vibration modes (received from step a/)

the sum of forces ("Sum of forc.") is calculated in the following way:

a/ first for each vibration mode the sum of forces ("Sum of forc.") is calculated by adding (linear combination) all pseudostatic forces of appropriate mode

b/ then the sum of forces for CQC combination is calculated as the CQC combination from the sums of forces for individual vibration modes (received from step a/)

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@faisal.aaouatif wrote:

2.When using Reaction table; Values of shear force at the base of a building are those on columns corresponding to the "somme of reaction" record [ and not those on somme of values ]

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Yes, the base shear can be obtained as "Sum of reac." or "Sum of forc." (they are equal).

"Sum of val." should not be used for this purpose because:

a/ it is considering only supports currently filtered (displayed) in the table of reactions

b/ even if the filtering is displaying all supports the sequence of combinations is incorrect because in such case first CQC combinations from all vibration modes are calculated for individual supports and then they are all added (linear combination). So the sequence of combinations (linear and CQC) is opposite than for "Sum of reac." or "Sum of forc."

Regards,

[Pawel.Pulak · Accepted solution]

1.from the RSA Help it is stated that :

"In quadratic combinations for cases of the seismic or spectral analysis, the sum of reactions and the sum of forces are calculated by adding the values of the respective sum of values and the sum of forces for individual vibration modes"

Can we have a little more explanation ie : the somme of reactions are equal to ....

and the somme of forces are to....

---

[Pawel.Pulak · Accepted solution]

2.When using Reaction table; Values of shear force at the base of a building are those on columns corresponding to the "somme of reaction" record [ and not those on somme of values ]

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