Value of behaviour factor - q

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@ Tomasz Fudala

Dear
Why robot calculate displacement values due to elastic spectrum data by EC8.
The value of q factor does not affect displacement values,
To be more specific, if you use q =1, q=1.5, q=2, or any other value of behaviour factor in response spectrum data, you will give same values of displacements ( regarding to EC).

Regards

[waldemar.okapa]

Robot calculate EC8 seismic load with elastic or design spectrum. Behaviour factor q reduces design spectrum.
According to EC8 p.4.3.4 displacement from design spectrum should be multiplied with q factor. In effect, forces are reduced with q factor but not displacement.

[length zero]

@ waldemar.okapa

From my experience with robot i tell you so:
To calculate displacements of structure due to seismic load, robot is not taking into consideration value of behavior factor given in spectrum datas ( it is calculating disp. with q=1 only)

I tell you an short example
If u define 3 seismic cases with same spectrum datas with variyng values of q, you will get this

1.Spectrum 1 ( q=1) - robot give d=10 cm
2.Spectrum 2 (q=2 ) - robot give d=10 cm
3.Spectrum 3 (q=3 ) - robot give d=10 cm

If i multiply displacement from case 3, 10x3 = 30 cm,
In order robot must give dispalcements from case 3 - 10/3 = 3.33cm
( aproximately)

Regards

[waldemar.okapa]

I suppose that the results for design spectrum are correct. Just keep in mind that the displacement are already multiplied with q factor, as required by EC8.

In your example, lets consider also sum of reaction FX, Robot gives:
1.Spectrum 1 ( q=1) - FX=30, d=10 cm = 1*10cm
2.Spectrum 2 (q=2 ) - FX=20, d=10 cm = 2*5.0cm
3.Spectrum 3 (q=3 ) - FX=10, d=10 cm = 3*3.33cm

[mecheil2000]

@ waldemar.okapa

From my experience with robot i tell you so:
To calculate displacements of structure due to seismic load, robot is not taking into consideration value of behavior factor given in spectrum datas ( it is calculating disp. with q=1 only)

I tell you an short example
If u define 3 seismic cases with same spectrum datas with variyng values of q, you will get this

1.Spectrum 1 ( q=1) - robot give d=10 cm
2.Spectrum 2 (q=2 ) - robot give d=10 cm
3.Spectrum 3 (q=3 ) - robot give d=10 cm

If i multiply displacement from case 3, 10x3 = 30 cm,
In order robot must give dispalcements from case 3 - 10/3 = 3.33cm
( aproximately)

Regards
it is an important information Zero Length...
Thanks for this conclusion...

[Marios]

The important conclusion is given by waldemar.okapa.
Try those calculations in the region of spectrum where T<TB.The factor q cannot not be eliminated from the right part of the spectral equation when multiplying both parts with q.

[length zero]

I'm posting an official email which i get via some friends:



Dear Sir,
I have checked the models you send.
According to EC8 the behavior factor is defined to reduce the seismic forces because of the capacity to
disipate energy. The displacement of the structure must be calculated without the behavior factor. In
some local codes (for example the romanian P100) the program calculates the displacement with the
behavior factor included and the user must multiply that value in the end by the behavior factor.
In EC8 the program always calculates the displacement with behavior factor 1.

The answr is from service of altiscad-romania.



I hope thate this is so.
I have red manuals and i havent find anything for this purpose in robot.
It is very interesting thing, and i dont know how they have ignored in description in manuals.

Regards

[mecheil2000]

I agree with u
We need a clarifaction for seismic parametres of robot
I face same problem with ubc code

[mark.martin.se]

Hi to everyone....

.....I experienced same problems in earlier versions of Robot! Though I can't understand why the issue still persist! I mean, it's not something so difficult to reprogram!



Regards!

[medo]

Hi to all,

I have tested a high-rise RC structure by using Robot Millennium 20.1.5 with Eurocode8 (EN 1998-1-1:2004).

As seismic input parameters behavior factor was varied with values q=1, q=2, q=3.5 and q=5 while ag=3 m/s^2, ground type C, design spectrum of type 1 in horizontal direction was used. The following summarizes the top displacements and total seismic forces read from CQC combination:

q=1.0 Ux=13.4 cm; Uy=17.2 cm; Sx=34099.55 kN; Sy=33857.10 kN
q=2.0 Ux= 6.7 cm; Uy=8.6 cm; Sx=17064.87 kN; Sy=16965.70 kN
q=3.5 Ux= 3.8 cm; Uy=4.9 cm; Sx= 9766.93 kN; Sy= 9727.55 kN
q=5.0 Ux= 2.7 cm; Uy=3.4 cm; Sx= 6894.95 kN; Sy= 6833.16 kN

It seems that the displacements and forces are divide with the behavior factor!
If you, for instance, divide Ux for q=1 with Ux for q=5 you get 4.96
divide Ux for q=1 with Ux for q=3.5 you get 3.53
divide Ux for q=1 with Ux for q=2.0 you get 2.00

The same applies for forces.

[lucis29]

I'm using the Romanian Code (P100)

The code say:
To compute the displacement at SLS, multiply the displacement resulting from linear analysis with a 0.4 and q
dr=0.4*q*dr_robot

To compute the displacement at ULS, multiply the displacement resulting from linear analysis with a factor c=3-2.5*T/T.c<2 and q.
dr=c*q*dr_robot

I'm doing the following for computation of displacements:


1) I make a model and compute it with q=4 (for example), then read the eigen mode period (T).

2) I change q such that the new q_SLS=q*0.4 (ex. q_SLS=4*0.4=> q_SLS=1.6), read the displacements values and compare them with the allowable ones in the code.

3) I change q such that the new q_ULS=q/2*q (ex. q_ULS=4/2*4=> q_ULS=0.5), read the displacements values and compare them with the allowable ones in the code.

Shortly: I just modify q with an expression q*[something<1].

A question:

Where do you read the story drift values?