Earthquake case - support gap

ROHR2 Dynamic calculations, questions and discussions
ROHR2stoss - Structural Analysis with Dynamic Loads using Direct Integration
Antworten
Benutzeravatar
r2user
Beiträge: 135
Registriert: Mi 14. Sep 2011, 10:18

Earthquake case - support gap

Beitrag von r2user » Mo 26. Sep 2011, 07:11

Dear Sir,

There is a specific enquiry regarding Rohr calculation in earthquake case, when there is a support with gap. Rohr is considering that as without gap in case of earthquake. So that is impacting stress value as well as support load .

*Stress analysis*- In 'operation load case ' due to gap in support (mainly guide and axial ) stress is reducing & at the same time considering same support with zero gap in 'earthquake' , falsely showing reduced values of occasional stress.

*Support load*- Due to zero value of gape in occasional case , falsely giving load on support which is increasing extreme value also.

In my Rohr file at node *611* and *629* inspite of gap in these supports, in Rohr calculation zero gap is taken for earthquake.

Best regards

Benutzeravatar
rohr2support
Beiträge: 393
Registriert: Mi 14. Sep 2011, 08:23

Re: Earthquake case - support gap

Beitrag von rohr2support » Mo 26. Sep 2011, 07:21

Dear Sir

In Rohr2 you can select linear or non-linear load cases.
In linear load cases you cannot considder any non-linear supports (e.g. gap)

Rohr2 will allow you to create a linear system from an non-linear by:
- neglecting friction
- converting supports with gap in either supports with no gap in that direction or no support at all (free) in that direction.
The choice is made upon the value "gaplim" which you can set with Project Settings->Gap with linear calculation (e.g. 8mm) which means that all supports with more than 8 mm of gap are considered free in the linear load case.

I assume that your earthquake case is calculated linear therefore no gap will be taken into account.
Of course you can switch on non-linear calculations but this would require carefull combination with the underlying operation conditions to get reasonable results.
r2user hat geschrieben:*Stress analysis*- In 'operation load case ' due to gap in support (mainly guide and axial ) stress is reducing & at the same time considering same support with zero gap in 'earthquake' , falsely showing reduced values of occasional stress.
Yes you will get probably reduced stresses for linear calculation and therefor you should not use a big value for "gaplim"
r2user hat geschrieben:*Support load*- Due to zero value of gape in occasional case , falsely giving load on support which is increasing extreme value also.
Please remember that we are talking about a dynamic load case which is just a huge simplification of a dynamic event.
In case of earthquake you will get very high local loads at supports which have gab and which are free to move within this gap.
Basically due to the dynamic effects it can actually "hammer" onto the support rather than applying a static load.

In short: Support with big gaps:
DONT DO IT!
FOR EXPERTS ONLY: DONT DO IT YET!


Best regards

Antworten

Wer ist online?

Mitglieder in diesem Forum: 0 Mitglieder und 1 Gast