Seismic analysis with maximum seismic acceleration and Newmark combinations

[Anonymous]

Dear all,

I am a beginner in Robot software and I would like to analyse a metallic frame composed by beam elements during seismic event.

I know the maximum seismic acceleration on the X, Y and Z directions and I would like to combine the three directions with Newmark's rule:

S=+- SX +-0.4 SY +- 0.4 SZ

S=+- 0.4 SX +- SY +- 0.4 SZ

S=+-0.4 SX +- 0.4 SY +- SZ

Is it possible to run seismic analysis applying the maximum seismic acceleration (Static equivalent method without modal analysis) with using Newmark combinations?

Thanks a lot for your help,

Best regards,

Frédéric

[Artur.Kosakowski]

If I understand you correctly and SX; SY  and SZ are the static seismic load cases it should be enough to define combinations among them with the load factors as you described them.

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[Anonymous]

Yes I defined single load cases  (DW, LL, SX, SY and SZ). These single load cases should be combined with eurocode rule:

DW+LL +- SX +- 0.4 SY +- 0.4 SZ

.....

.....

.....

But is it possible to do automatic combinations?

[Artur.Kosakowski]

Automatic generation of Newmark combinations is done for seismic response spectrum analysis only. The static seismic cases will get =1 and -1 factors by default.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Ok thank you very much for your answer.

My last question is:

I saw that it is possible to create manually the combinations but is it possible to import a file (e.g. excel file) or create quickly the combinations in order to avoid to enter manually the 24 combinations?

The process with robot seems to be longer.

Thanks very much.

Frédéric

[Artur.Kosakowski]

Yes, you can copy and paste them from Excel provided in Excle you defined the combinations with the columns as marked in yellow:

Name / case number / load coeff / case number / load coeff / 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Ok thank you very much, it works very well...

I have another question about the single load case:

When I launch the single load case SX, the reaction forces show that the inertia force is only apply to the mass (converted from load) but not on the structural frame which is modelled by beam.

I have defined the single load cases (see picture in attachement), is it something missing?

Thanks very much for your answer,

Frédéric

[Artur.Kosakowski]

If you mean self weight then this is done automatically. 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Actually during seismic event in X direction, the seismic acceleration should be applied on the mass converted from load and the mass of the structural frame.

But the reaction force on SX show that the seismic acceleration is only apply on mass converted from load and not on the mass of structural frame.

Mass converted from load: 45000kg

Mass of structural frame: 740kg

Seismic acceleration on X direction: 32.4m/s²

Result from Robot:

Reaction force on single load case SX: FX=1 458 498N

While the reaction force should be FX=1 481 976N

Does it miss to define a additional load on the single load case SX (see picture in attached file)

Thanks very much for your answer.

Best regards,

Frédéric

[Artur.Kosakowski]

I'm not sure if I understand you correctly. Did you define seismic (equivalent lateral force method) analysis or just define body forces (which you consider as a seismic load) for selected load case(s)? Could you attach the model please?

[Anonymous]

Yes I defined just body forces.

I have attached the model.

Thanks very much for your answer.

Best regards,

Frédéric

[Artur.Kosakowski · Accepted solution]

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

It works much better.

Thank you very much 😉