Moment Connect. Design

[palk7 EIT]

Hi,

It is a very basic question, but just trying to get in there. When designing a moment connection at the beam-column connection, what should be that moment connection designed for either the beam end moment or the moment transferred to the column?

Thank you

 

[jayrod12]

The beam end moment. If there's a beam on the opposite side of the column that takes some of the beam end moment out of the column it is still required to transfer the full beam end moment to the column, and then part of it gets transferred to the next beam.

If there is no beam on the opposite side of the column, then the beam end moment should be equal to the column moment.

 

[jk2017]

The connection has to transfer the full beam end moment to the column, assuming there isn't a beam opposite the one in question that could take some of that moment.

 

[palk7 EIT]

Thank you very much, no opposite beam on the other side. So, the connection to be for full beam end moment, but while analyzing the column at that point the column doesn't get the full moment right? I mean due to varying stiffness of beam and column the column receives certain share of that moment is that to be considered?

 

[jayrod12]

If your analysis takes into account the full beam end moment for the beam design, then the column must take the full moment. Otherwise the laws of statics and equilibrium wouldn't be satisfied.

 

[dauwerda]

So, the connection to be for full beam end moment, but while analyzing the column at that point the column doesn't get the full moment right? I mean due to varying stiffness of beam and column the column receives certain share of that moment is that to be considered?

When you say, "full beam end moment" are you referring to the beam section capacity or the maximum moment developed determined by analysis?

 

[dik]

to be clear... not for the full beam moment capacity, but for the factored LL and DL moment.

Dik

 

[JoshPlumSE]

A few basic points of static analysis at any given point in a structure.

Sum of the Forces in the X direction = zero
Sum of the Forces in the Y direction = zero
Sum of the Forces in the Y direction = zero

Sum of the Moments about the X axis = zero
Sum of the Moments about the Y axis = zero
Sum of the Moments about the Z axis = zero​

It might be a little snarky of me to point this out. But, that's the basic reason why the end moment at the beam going into the column is equal to the moment in the column. For a single story frame, that's perfectly equal. For a two story frame (where the column is continuous past the beam), the difference in the column moments from above and below the beam would be equal to the beam's end moment. Just sum of the moments equals zero at that particular joint.

 

[structSU10]

I'm guessing you are seeing the moment be split between the column above and below the moment connection depending on its span / stiffness. If its right at the center of the column, there would be 1/2 the moment resisted in each half of the column that sum to the total moment applied by the beam.

 

[palk7 EIT]

Yes the moment is from analysis for the factored DL & LL, attached a pic, have 2 cases one above and below and node N4 is the one in question: So in the above pic (1st Case) I kept the end releases of both beam and column at that intersection to be fixed and get a moment of 5kip-feet for both beam and column have the same moment as mentioned by jayrod12. In the second case what I did was added fixed support there at Node N4 and if you could see the beam there is having higher moment 35kip feet at that joint.

I feel what I did in second case is wrong to put again a fixed support at that joint, is this true? cuz in second case only the beam is experiencing the moment there and it is not transferring anything to the column.
Appreciate your time

 

[JoshPlumSE]

I feel what I did in second case is wrong to put again a fixed support at that joint, is this true?

Your first case looks right to me. There isn't much moment at the end of that beam. But, what does exist goes into the column.

The second one is NOT correct. Added a fixed Boundary Condition to the top of the column creates an artificial restraint inside your structure. Boundary conditions should only be used to represent how a structure connects to the outside world. Usually at the base of a column you have a pinned or fixed boundary condition to represent out the column connects to some foundation or mat or such.

 

[palk7 EIT]

thank you Joshplumse, what did you want to ask reg. " what does exist goes into the column".?

 

[JoshPlumSE]

Slight language barrier.... It could be rewritten as "The moment that does exist goes into the column."

 

[r13]

The 2nd case can occur if the beam is attached to a wall with moment connection, and a simple shear connection between beam-column interface.