END RELEASES IN ETABS QUESTION 4

[eyemeyar]

HELLO EVERYONE. I WOULD TO HEAR YOUR IDEAS ABOUT THE USE OF "END RELEASES" IN ETABS.

1 - WHEN IS IT ALLOWED TO BE APPLIED IN BEAMS AND COLUMNS?
2 - AREN'T THE CONCRETE BEAMS AND COLUMNS SUPPORT SHOULD ALWAYS BE FIXED?
3 - CAN SOMEBODY TELL ME THE PURPOSE WHY WE SHOULD PUT END RELEASES?

THANK YOU VERY MUCH. =)

 

[williechai]

1) when the user want to change the support condition of frame element (column or beam).
2) Support condition depend on the designer design intention. There are some cases where support condition for column/beam need to be pin instead of fix. Example such as steel column connect to RC column where it is more economically to design as pin-pin connection.
3) Same as 2).

Hope this help.

Willie

 

[eyemeyar]

Thank you for your kind respond. I so appreciate it. =)

1 - Is it even allowed to change the support condition of concrete frame element from fixed to pin?
2 - I saw some designers applying end releases on edges of concrete beams & columns if it is not a cantilever, is that allowed? This will eliminate the moment transferred from the beam to column. Isn't that dangerous, neglecting the moment transferred to the column from the beam?

Thanks. =)

 

[williechai]

Hi,

It is allowed to change the support condition even for concrete frame element.
However, the designer need to ensure the changes are reasonable and justifiable.
The designer need to ensure the oversll structutal stabiliy will not be affected.

For structural where there is not core wall, beam to column connection need to be fix to creste s moment frame effect for stability.

If core wall exist, there is a posibility to pin the beam to column connection and relying purely on corewall to achieve the structural stability.


I have listed two examples below of pin condition for your thought:

1) Secondary Rc beam to main RC beam connection
The connection of secondary beam to main beam can be pin-pin in view that RC beam will normally not designed to take torsion. If fix fix would be apply, your main beam to design for torsion and your provided shear link need to be loop link to resist the torsion effect.

2) RC beam to RC wall connection
Normally RC wall is week in minor axis. If RC beam would be connected to minor axis of RC wall, the connection need to be pin where the moment will not transfer to RC wall minot axis.


Hope this can clear your doubt.

 

[eyemeyar]

Thank you very much...

If I understood it right, fixed support for concrete frame element can be replaced with pin connection to eliminate torsion in case of secondary to main beam, and so that there would be no moment transferred to core wall if it is applied on the weak axis..

If we made the concrete frame connections pinned in the analysis, shouldn't we also make it pinned in actual construction? I would like to know how is it done on cast in place concrete construction. For all I know in actual, it should be a fixed connection. This is really what bothers me most. =(

Thanks. =)

 

[brick2011]

Also, when you "release"secondary beams, please make sure you pay attention to the detailing. Full Ld should not be provided.

 

[eyemeyar]

brick2011,

oh. . I see.. Does that mean if I don't provide full Ld on my concrete beam supports, no moments will be transferred to the adjacent frames because it will behave as simply supported? In that case, If we want a fixed support we provide full Ld, For simple support don't provide full Ld. Therefore, Moment reactions are just a matter of Ld provision. Is that it? I wish to hear more from you...

Thank you very much. =)

 

[brick2011]

I never meant to say moment is just a function of Ld... detail the secondary and primary beam connection accordingly.

engineering is in the details..

 

[serrojo]

It is very important to create the correct detailing, because if you got seismic load it is recommended to accomplish certain flexibility to dump some energy, sometimes you can do this by placing the rebar in crossed position on the beam column connection (see the attached picture).

MSc. Eng. Serguei Joa
Tel: +5352460358
mail: sm.joa@bouygues.cu

 

[RulaTamimi]

there are cases for the joint condition, if you dont wish to transfer moment from beam to column (shear walls and frame elements take moment and seismic load) , depending on the structural system desired.
then you should release moment at beams and columns.

 

[eyemeyar]

Can u show me how joint reinforcement detailing is done for released and unreleased moment?

Thanks. =)