Displacement missing

[sribeiro]

Dear STKO team,

I've been following the Eigenvalue and Response Spectrum Analyses (https://www.youtube.com/live/vUXKVm5_rn ... xdVuU_8Wsx) video to better understand the modes of vibration of my structure.
Although I followed all the steps of the video, when I run the analysis I can't see my structure's displacement - as you show on min 45 of the video - and also can't obtain as much time-steps as the example gets.

The structure was modelled using columns with rectangular fiber sections, and the deck is a shell element with ASDConcrete3D material. (model file in annex).

Am I doing something wrong?
Do you think the problem is on the mass of the structure?

I also saw that in another video Ms Marafini uses a generic surface load, is it a better option compared to the facemass command to define mass?

Thanks!

[STKO Team]

Try to solve one problem at a time.

when I run the analysis I can't see my structure's displacement

First off, your first analysis only does an eigenvalue analysis.
The previous analysis has 0 steps (so it's a no-operation). It's just used to set up the settings to be used later by the eigen analysis. (but to do so, you have to remove the wipeAnalysis flag, otherwise it's useless).

Even if you put a non-zero number of time steps in that analysis, you won't see displacements, just because you did not put any load in a load pattern!

But before looking at this, try to solve your main issue. Your foundamental period is 120 seconds! something is wrong. Check the masses and keep in mind you are modeling in N-mm, so the concrete mass density is about 2.0e-9

[sribeiro]

But before looking at this, try to solve your main issue. Your foundamental period is 120 seconds! something is wrong. Check the masses and keep in mind you are modeling in N-mm, so the concrete mass density is about 2.0e-9

Thank you very much for your reply, I did recheck the values of the masses and yes, something was not right.

I got now displacements and much lower period values. However, I believe they are still not low enough, do you know what can be the problem? Should I include rotational mass too?

I would also like to confirm something: when we use a Faceforce and Facemass, the load is F/area (N/m2), correct?

Thanks!

[STKO Team]

There are still errors with the units you are using.

From the values in your materials (for example fc = 30000) I can see you are using kN-m.
But then your masses are set up as kg.
Also in the ASDConcrete3D fc = 30000 but you said it's N-m. 30 Mpa = 30000 kN/m**2...

Also, in the section you set the cover at 5 mm... are you sure it was not 5 cm?