Moment Connection - Steel Beam to Precast Column

[MindofBarca]

Hello All,

I have a design question for those familiar with precast and steel connections. I am designing the precast concrete for a 2 story podium style mixed use building. On the exterior of the building I have some precast columns which are supporting two wide flange steel beams. These connections have been called out by the EOR to be moment connections. I am looking for some advice/guidance as to how these members should be connected. The original detail the EOR called out for was simply extending the precast columns up to TOP OF BEAM elevation and butting the wide flange beams into a cast in embed in the precast columns. The problem with this detail was getting my studs to work in shear (I hadn't even got to the moment design issue). In discussing with the EOR we decided to drop the TOP OF PRECAST to BOTTOM OF STEEL BEAM and sit the wide flange members over the top of the column (with a 1" gap between both beams). This eliminated the need for two cast in embeds in the face of the columns. Now I just have to figure out (hopefully with your help) how these members are connected. Can I simply cast in an embed to the top of the column and weld the wide flange members to the column plate? Will this satisfy the "moment connection" needs?

Here are some examples of the loads to get a better feel for the project:
- 18x18 precast column
-Shear= 100-150kips (per beam)
-Moment = 290 k-ft

It's also important to note, most of the columns we typically design are simply supported, K=1.0, type columns. Does this change my column base connection?

Thanks in advance,
jReck

 

[KootK]

How big of a deal is seismic on this project?

It's also important to note, most of the columns we typically design are simply supported, K=1.0, type columns. Does this change my column base connection?

It may not change your base connection but it will almost certainly mean K > 1.0.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Do they need the moment connection to the column, or was the intent to just have the moment connection so the beam acted continuously through the column?

 

[KootK]

Also, given that it's a two story thing, is it important that your column be two story units? If so, the lower beam connections would have to be to the side of the column, right?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MindofBarca]

How big of a deal is seismic on this project?

Not a concern. Project is in mid-west.

Do they need the moment connection to the column, or was the intent to just have the moment connection so the beam acted continuously through the column?

Good question, I can follow up with EOR and verify his intentions.

Also, given that it's a two story thing, is it important that your column be two story units? If so, the lower beam connections would have to be to the side of the column, right?

These columns in particular do not support 1st level members, they extend through the 1st level and just pick up these 2nd floor wide flange members.

Thanks for the replies.

 

[KootK]

I can imagine some options for side connection but, like you, I prefer over the top. The advantages as I see it:

1) More robust because you're not trying to anchor an incoming horizontal flange force near the top of the column where you've got to contend with edge distances.

2) I like not having to deal with high panel zone shears within the concrete column.

3) Easier to make it look sexy.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MindofBarca]

I can imagine some options for side connection but, like you, I prefer over the top. The advantages as I see it:

1) More robust because you're not trying to anchor an incoming horizontal flange force near the top of the column where you've got to contend with edge distances.

2) I like not having to deal with high panel zone shears within the concrete column.

3) Easier to make it look sexy.

Glad we are on the same page. I was thinking of something very similar. See below:

Not sure if a fillet weld (as shown) would be correct or not for this type of connection?

And I misspoke earlier, the columns are 16x16 as shown in the detail above.

Thanks again.

 

[KootK]

I think that something like that would be suitable for simply making the beam continuous (jayrod). I don't love it for actually transferring moment into the column, however, if that is in fact the intent. I'm guessing that it's not the intent. A two story moment frame without an intermediate tier would be pretty soft.

Either way, I'd think that you'd want at least one vertical stiffener in there to help out with lateral torsional buckling.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Teguci]

290 ft K suggests that you need to put the moment forces directly into the precast column rebar - something like (4)-#10 per face. You could lap in some DBAs but HASs don't make sense to me. I'd also suggest making one beam continuous over the column and provide a moment connection for the other beam at a more advantageous location (where there is less moment). Welding to an embedded plate requires care since heat will expand the plate. Especially in this case where the welds will be significant.

Maybe, fabricate a column cap and shoe to provide for the 8 bolt connection (4 - 1 1/4" bolts per side). The column cap will have DBAs that lap with the precast rebar and will have side pockets to receive the bolts and nuts (MC4 facing out with cap plate and stiffeners?). The shoe will have matching holes and appropriate stiffeners to transfer the load into the beam.

 

[MindofBarca]

290 ft K suggests that you need to put the moment forces directly into the precast column rebar - something like (4)-#10 per face. You could lap in some DBAs but HASs don't make sense to me. I'd also suggest making one beam continuous over the column and provide a moment connection for the other beam at a more advantageous location (where there is less moment). Welding to an embedded plate requires care since heat will expand the plate. Especially in this case where the welds will be significant.

Maybe, fabricate a column cap and shoe to provide for the 8 bolt connection (4 - 1 1/4" bolts per side). The column cap will have DBAs that lap with the precast rebar and will have side pockets to receive the bolts and nuts (MC4 facing out with cap plate and stiffeners?). The shoe will have matching holes and appropriate stiffeners to transfer the load into the beam.

Thanks for the response, could you provide a detail or quick sketch of your ideas please? Trying to visualize everything.

 

[Teguci]

 

[dik]

JReck... Your connection at the top is similar to what I've done... might move your splice point to about 1/7 span and use ql^2/12 for your design moment and use a bolted end plate for shear and moment transfer. With the continuity, your deflection is greatly diminished... about 1/3 of the simple span deflection. Add a stiffener plate at the support...

Dik

 

[MindofBarca]

Thanks for all the responses, I really appreciate it!

 

[hokie66]

I would doubt the EOR wants to transfer that much moment into a 16x16 column, but think he just wants to cantilever the beam. But he is the one who should be making this decision, not us.