etabs problem

[yasir1989]

hi everyone
Q1) why etabs dont consider the change in accidental eccentricity so all base shear results are the same whatever the value of accidental eccentricity ?
Q2) i have rectangular building (40x20)m, why the natural frequency in the orthogonal directions dont have a big different ?
Thank you

 

[yasir1989]

Hi to every one,is there anyone reading this...........I m waiting for a good reply to my question????

 

[inggelu]

Hello there,

Can you upload the model to the building and see how is configured?
Also can you tell what do you understand when you say natural frequency? You refer to the building period?
I will waiting your model and we will discuss after that.
It is difficult to take a conclusion without more information.
Also it is important if is an concrete structure or steel structure.

 

[yasir1989]

hello inggelu
my problem
i have rectangular building(40x20) and the the natural frequency (building periods) in the orthogonal directions dont have a big different( i use sap2000)
thank u

 

[inggelu]

Hello,

Sorry but I can't help you my version of SAP2000 is older then the file was created.
If you can export on older version of SAP2000 (v 15.0.0) to be able to open I will do the best.

 

[inggelu]

Hello again,

I check your model (finally) and looks ok. I don't think is a problem with the building frequency.
I don;t know on what code you working on but you alway check the frequency of the building (approximative of course)
with the next formula (for building up 40m high)

T1=Ct * H^(3/4)


T1- is the fundamental building period in seconds

Ct - is one coefficient depending of the structure
Ct=0.085 steel frame structure without bracing
Ct=0.075 concrete frame structure and steel structure with bracing
Ct=0.05 other structures

H - is the building high in meters.

Yes is true your structure is about 75m high, but you can reduce the high of the building under 40m let's say 21m or 24m and see what is happens.
The formula I give to you is checked and is a very good approximation. I checked with structures about 12m high.

After you check with this new information hope you will be clarify.

Good luck.