Web Doublers

[mokeenels]

I'm a recent graduate and am working on my first steel connection design package. The connection I am working on is an extended end plate moment connection between a w21x62 beam and a w10x77 column. I was able to design the end plate but was running into issues with the web panel zone shear of the column. I wasn't given any design moments so I used the full capacity of the beam, 540 k-ft. The web panel zone capacity is 151 kips and the force in the flange is 332 kips. Are web doublers the only option in this case? The client wants to stay away from them at all costs.

 

[JoshPlumSE]

Lots of possibilities:
1) You used the full capacity of the beam..... Use the actual demand moment. Is this an SMF or IMF seismic moment connection, where you are required to design for the "maximum probable moment" per AISC 358? If not, then this part of the design is overkill.
2) It is often more efficient to use a column with a thicker web than to add doubler plates.
3) You could add a haunch to the connection to reduce the flange force. This usually adds about 50% to the beam depth. Which, therefore, reduces the flange force by 33%.

 

[CANPRO]

There is often information for proper connection design missing from drawings. The first thing I do when I get a set of drawings is review the entire package and generate a list of questions to send to the EOR - one of the big ticket items is missing design loads for moment connections. If the EOR is reasonable you'll get the actual design load, but sometimes you're stuck designing for the full capacity.

On the topic of designing for the full capacity of the beam - the moment resistance of your beam exceeds the moment resistance of your column by almost 50%, so unless there is a balancing moment on the opposite side of the column, your column can't handle the full beam moment and there is no point in designing the connection for that value - the full moment value of the column might be more appropriate.

An alternative to doubler plates would be inclined stiffeners in the web of the column - have you considered this option?

 

[TLHS]

I agree that clarifying the design load is important. If it is a large moment, along with checking if a haunch is acceptable, you can also see if a small kicker knee brace would be an acceptable alternate. It's fine in a lot of cases and is overlooked by the design engineer when they don't have to work out the connections.

If you are contracted by the fabricator, it might make sense to ask them if they want the web doubler or if they could do the work cheaper if you ask the EOR for permission to increase the column web.

 

[Agent666]

Depending on how the beam moment is distributed and the geometry, the column could take up to double its capacity if half the moment distributed above and below the beam.

Deeper column is the other option not mentioned yet.

If the client didn't want Doublers then shouldn't they have allowed for that in the member design? Going to the minimum member size often means jumping through more hoops for the connections.

 

[txeng91]

See below from AISC design guide 13. This is based on 14ft floor to floor heights.

 

[mokeenels]

Thanks for all of the responses everyone. I reached out to the fabricator and they are sending an RFI for the required moments.