Displacement calculation under seismic analysis

[faisal.aaouatif]

Ive run two seismic analysis under Eurocode 8 ; the first one with behaviour coeff = 3.90 and the second with behaviuour coefficient = 1.00 ; ive got slitly the same results in term of displacement at the stories table.

so , Please confirm that the displacement calculated at the stories table are the elastic one , and they should be multiplied by the behaviour coefficent in order to the obtain the correct ones when doing seismic analysis ( with behaviour coefficient greater than 1.00)

In advance Thank you.

[Pawel.Pulak · Accepted solution]

Displacements in EC8 are in case of design spectrum already multiplied by behaviour coefficient q.

In case of T>TB it results (independently from q value) in displacements equal to displacements from elastic spectrum.

If some vibration modes with significant mass participation are observed for T<TB it may result in slight differences of displacements depending on q value - as it the screen captures attached to your post.

This effect results from comparison of analogous branches of elastic (formula (3.2)) and design (formula (3.13)) spectrum - the difference between them is more than just division by q, as in other branches of spectra.

---------------------------------------------
If this post answer your question please click "Accept as Solution". It will help everyone to find answer more quickly!

Regards,

[RRufino]

Hi pp2008,

regarding "Displacements in EC8 are in case of design spectrum already multiplied by behaviour coefficient q."

This is a valid statement only for stories tables or also to nodal displacements table and diagrams for bars (deformation) ?

Thanks.

[Pawel.Pulak]

 RRufino:

This is a valid statement only for stories tables or also to nodal displacements table and diagrams for bars (deformation) ?

Yes, it is a valid statement also for nodal displacements and diagrams for bars.

---------------------------------------------
If this post answer your question please click "Accept as Solution". It will help everyone to find answer more quickly!

Regards,

[RRufino]

Hi all,

I'm pulling up this topic to ask if in the following example, using arsa 2014 and Maroccan Code RPS 2000 to define seismic action, storey drift and other nodal displacement outputted by arsa are already affected by behavior factor?

I suppose yes but when i change behavior factor nodal displacements don't change.

Thanks in advance,

RR

[RRufino]

Dear all,

Is it possible to get a look to my question?

Thanks,

RR

[Pawel.Pulak]

---

@RRufino wrote:

I'm pulling up this topic to ask if in the following example, using arsa 2014 and Maroccan Code RPS 2000 to define seismic action, storey drift and other nodal displacement outputted by arsa are already affected by behavior factor?

I suppose yes but when i change behavior factor nodal displacements don't change. 

---

May be  it is surprising but nodal displacements don't change because they are affected by behavior factor. 

Forces, moments and reactions are reduced because the seismic action is divided by the bahavior factor. Displacements are not changing because they are additionally multiplied by the bahavior factor.

Division combined with multiplication results in no change.

I have shown this on the screen capture below - for behavor factors eual to 3.5 and 1.0

Regards,

[FilRib]

So, for my final calculations should i use the values provided in the table or do i need to affect them with the behavior factor? honestly i got i little bit confused.

Thanks in advance! 

[Pawel.Pulak]

---

FilRib wrote:

So, for my final calculations should i use the values provided in the table or do i need to affect them with the behavior factor? honestly i got i little bit confused.

---

You should use the values provided in the table.

Regards,

[RRufino]

Thanks Pawel.

Best Regards,

RR

[FilRib]

Thanks! 

[fareed12]

good  day can I use (Umax &Uavg)Displacement directly from Response spectrum use ubc97  to get(Ax) Torsional amplification factor I was asked but nobody answered