Moment Connection Values for Design

[nicholi]

I need some assitance in determining the values for moment connection designs. We have to provide the value of the moment connection at the joints that are fixed in a rigid frame for the steel fabricator to do the MC design. I used P-Frame Lite to complete the rigid frame analysis and have all the moment loads for the different members ending at that joint. However when I sum the moments at that joint it = 0, which means there is equilibrium at that joint and the moment has been distributed to each member. What value to I give to the designer to design the moment connection?

Thanks in advance for the advice.

 

[TFL]

all the moments should sum to zero. each member framing into the joing should be designed for the load in induces on the joint*1.25 increase for safety. the capacity would also be subject to the limitations of the aisc seismic design criteria if that is required by the location

 

[CSEllc]

If you are using a "fixed moment connection", with full penetration welds between the beams and the columns, then no moment value needs to be given. The welding of the beam to column inherently provide you a joint which provide the full beam or column capacity (whichever is smaller.) Be careful if your column is weaker than your beam.....you could have a buckling issue in a seismic event

 

[DaveAtkins]

The connection should be designed for the moment at the end of the beam. Basically, the shear at the end of the beam will be taken by a double angle connection or shear plate, and the moment will be resisted by the connection of the flanges to the column (welded or bolted). The column may need stiffener plates as well, in line with the beam flanges. As a rule, I put the stiffener plates in.

DaveAtkins

 

[CSEllc]

tfl, and Dave,

If you are useing a full penetration welded moment connection, there is no "design". As I stated before, the welding fu8ully connects the beam to the column so the full capacity of the member is achieved.

 

[nicholi]

To all, thanks for the feedback. So on the drawings do I put down the values of moment for the beam at either side joint (column)?

 

[TFL]

CSELLC,

I agree that if the fabricator provides a full pen weld. there is no design value. the original post says nothing about a full pen weld or developing the full capacity of the member. there is no reason to develop the full capacity unless required to by the forces induced. the exception to that being the aisc seismic requirments which require a certain percentage of the section's capacity be developed. a moment connection designed for some percentage of the maximum moment is still a "fixed" connection as long as it can not rotate under design events.

Nicholi,
yes i typically put a reaction value on plan at the end of the members framing into the column. i would not use less then 50" of the capacity of the beam as standard practice or 125% of the calculated reaction which ever is greater.

 

[TFL]

sorry 50" should be 50%

 

[nicholi]

tfl, is that value for beam capacity the Mr value or Mr', the value at unbraced length, and the lenght given is the point where the in rigid frame the moment goes from positive to negative moment?

 

[TFL]

Mr THE FULLY BRACED MOMENT CAPACITY