Simple and Rigid beam-column connection 2

[haythamsadeq]

Simple and Rigid beam-column connection


I have an enquiry about the simple and rigid beam-column connection in concrete structures.
The enquiry is divided into 5 questions:
First, can I assume in a multi story building braced with shear wall that the columns are pinned ended and the connection between the column and the beam is simple? And design the column as concentric column with axial load only & minimum eccentricity?

Second, if yes, Is the rebar detailing will affect the type of connection that I am assuming. That means if I have simple connection, no intersections and overlapping between beam steel and columns steel will be required to have simple connection?

Third, if I want to have rigid connection, should I detail the steel and the beam and overlap them in a special way to make sure the moment will be transferred from the beam to the column and thus I can design the column as uni-axial column?

Fourth, If I choose to make simple connection between the beam and columns, can I simply release the column in the ETABS and providing that all lateral force will be resisted by shear wall element?

Fifth, Dose continuity in concrete only provides sufficient moment transfer between the concrete beam and column with adding and steel overlapping??

It’s a very important topic and I want to discuss it with you.

Regards,
Haytham Sadeq,
Fresh Structural Engineer

 

[JAE]

[blue]"..can I assume in a multi story building braced with shear wall that the columns are pinned ended and the connection between the column and the beam is simple? And design the column as concentric column with axial load only & minimum eccentricity?"[/blue]

No, the columns and beams are tied together and will naturally form a moment connection. Some engineers do design the beams as simple pinned ends at the columns, but in their steel detailing they realize that there will be moment at the columns and then provide additional reinforcement for that moment. For the columns - you really should NOT ignore the moments from the beams.

[blue]Second, if yes, Is the rebar detailing will affect the type of connection that I am assuming. That means if I have simple connection, no intersections and overlapping between beam steel and columns steel will be required to have simple connection?[/blue]

No simple connections exists so this question doesn't matter.

[blue]Third, if I want to have rigid connection, should I detail the steel and the beam and overlap them in a special way to make sure the moment will be transferred from the beam to the column and thus I can design the column as uni-axial column?[/blue]

Usually the column reinforcement extends up through the floor/beam/slab system and is spliced within the column length between floors. The beam reinforcement extends through the column to the next beam on the other side, or is extended fully into the column and hooked at the end.

[blue]Fourth, If I choose to make simple connection between the beam and columns, can I simply release the column in the ETABS and providing that all lateral force will be resisted by shear wall element?[/blue]

You could release the columns in ETABS to put all lateral force in the shearwalls - thus creating a conservative shearwall design. However, the building will deflect under lateral loading and the beam/column moment frames will take load in reality. This load should be considered in your design of the beams and columns.

[blue]Fifth, Dose continuity in concrete only provides sufficient moment transfer between the concrete beam and column with adding and steel overlapping??[/blue]

I don't understand your question.

 

[rowingengineer]

haythamsadeq,
question 1.
"First, can I assume in a multi story building braced with shear wall that the columns are pinned ended and the connection between the column and the beam is simple? And design the column as concentric column with axial load only & minimum eccentricity?"
A brief back ground to "simple" multi storey building design is to assume the columns have zero stiffness during horizontal loading events and the shear wall takes all the forces, ie the column have "simple" connections at each end.
For vertical loading events you can assume (I noramlly don't like JAE) the column doesn’t take the moment due to unequal spans, cantilevers ect. I also note that the requirement for a Minimum Mv exists in some codes, this need to be transferred.

Question two.
There is a need for minimum reinforcement for connections between the columns and beams to be provided (this will ensure re-distribution of loads before failure). You will also need to transfer Mv if your code requries it. This reo should be provided thus that all reo has development lengths and laps to teh beam.

Question 3. agree with JAE

Question 4. Don't know of etaps, I use rapt.

Question 5. Don't quite understand question, but I would say that concrete alone doesn't provided sufficient continuity for analysis, normally there needs to be reo.

 

[haythamsadeq]

Thanks for your discussion

For Q 2:
I see that there is a debate about this simple connection assumption, JAE disagree and says that no simple connection exist, and rowingengineer says that column may be assumed to have zero stiffness and no moment will be transferred,
JAE answer for Q 4:
“ You could release the columns in ETABS to put all lateral force in the shearwalls - thus creating a conservative shearwall design. However, the building will deflect under lateral loading and the beam/column moment frames will take load in reality. This load should be considered in your design of the beams and columns.”

If I can do this and release the columns in ETABS, no moment will be transferred in the ETABS to the columns, and I can check only P-delta moments that comes from lateral deflection, if later deflection is under the limit, and P-delta moment will be around zero, so in this case, I can design the columns as concentric columns with minimum eccentricity,

For Q 5,
I mean: does the continuity in the concrete between the beam and column only will be sufficient to transfer the moment between the beam and the column without the need of adding more reinforcement in this connection?

and if the answer will no, and the concrete continuity will not be enough, so the assumption of pinned end column may be used, because NOT adding reinforcement will help in NOT transferring moments on columns., right ?


Regards,

 

[rowingengineer]

haythamsadeq,
Question 2:
There is difference in our opinions probably because you can either analysis this system using plastic or elastic solutions. JAE is using the elastic approach i believe (JAE please correct me if I’m wrong), While I am describing the plastic method. Both which I believe to be possible solutions. Basically the two different approaches can be summarised as: elastic, the column will take load so design it for this load. Plastic, the column will take load however once the column reaches plastic moment continue to deform but take no further load, This means as long as you provide minimum reo you can assume the column takes no load, hence simplify the analysis.

Question 5. you can see there is a minimum strength requirement inherently built into the plastic and elastic methods. This minimum strength is defined in most codes as something like 1.2*Mcr. So you need to connect the beam and columns with this minimum reo.

 

[haythamsadeq]

Thanks rowingengineer for this clarification

 

[Ltdog]

haythamsadeq,I think the dual system is more importent.if we design hyperstatic structure, the building shall have more safety and reliability. Do you think so?

 

[haythamsadeq]

Thanks Itdog,

can you explain what do you mean by dual system ? and hyperstatic structure ?

Thanks

 

[Ltdog]

haythamsadeq,firstly please note my name is Ltdog and not Itdog.

The dual system is composed of the double lateral-force-resiting members such as frame+shear wall or fram+brace .etc. If your beam connect rigidly to the column, your structural system become the fram+shear wall.
Besides the perimeter beams connect rigidly to the column at least,the interior beams can connect simply to the column.

Rigid beam-column connection make the system become hyperstatic and you can design according to plastic measure.

If you have any questions pls let us know.

 

[abusementpark]

Even if I were designing the framing for simple connections, I would still detail it to have some moment-resisting capacity.

Nothing wrong with adding a little redundancy to the system.

 

[csd72]

Haythamsadeq,

You will see in the code that there are strict criteria on when you can use minimum eccentricity without further analysis - mainly internal columns with no sway that have even spans.

You should never use minimum eccentricity for external columns as there is always a much larger eccentricity on these.

Sounds like you need to do some reading on this, a quick google reveals:

http://www.world-housing.net/uploads/RC_frame.pdf?pr=Array

http://books.google.co.uk/books?id=...LCnBg&sa=X&oi=book_result&ct=result&resnum=10

http://nisee.berkeley.edu/turkey/Fturkch3.pdf

http://www.nicee.org/RCFrames_TechBrief_NIST_2008.pdf

http://books.google.co.uk/books?id=...6q3tBQ&sa=X&oi=book_result&ct=result&resnum=9

A few of these are seismic, not sure if they apply in your case.