steel/concrete stacked columns

[struct_eeyore]

2-part question. I've got an unsavory condition where I have to stack a steel 6" sq.hss over an 8" wide (nom) column - see attached image. In addition to column vertical reinforcing, I've got a continuous concrete beam passing thru the top of said column - although, regardless of the concrete beam, I've still only got enough room for (2) anchor bolts.

1) I'm thinking that providing rebar welded to column face and embedded in the h/c topping is sufficient to satisfy the OSHA (4) bolt requirement - no?

2) The grout packed under the b.p will have a vertical edge that will be confined by whatever topping pours down into the notch around the column. Assuming that the topping is fully consolidated within the notch, is there any reason to be concerned about a perimeter/flare breakout around the base plate?

Any other concerns about the detail as presented? The ASD load from the column is ~64K (~910 PSI bearing on 4000 psi conc.)


[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1708028472/tips/SNIP_c1rjlg.pdf[/url]

 

[BSVBD]

eeyore...

1) I see you specified A706, rather than A615 rebar. Good - for welding! However, did you check availability?

1) I often specify F1554 Grade 36 Threaded Rod to be welded to A50 steel beams for various applications. However, in YOUR application, I would not depend on a thin 3" concrete topping to resist in compression or retain in tension, assuming "SOME" degree of lateral movement.

1) Consider specifying a weld plate embedded in top of precast that A36 round bar could be field welded to. OR... Flat bar welded to the column could also to field welded to a precast weld plate. OR... Flat bar welded to the column could also be mechanically fastened, with concrete screws or Heavy Duty screw anchors or threaded rod and epoxy/adhesive, to top of precast plank "CORES" - avoiding prestressed strands in webs (seek precast supplier field assistance, which "IS" common by reputable suppliers).

1) The 4-bolt OSHA issue would LIKELY be waived if you have sufficient connection to precast. I strongly discourage depending on the "loose" bar in 3" topping. You would also be depending on local inspector approval.

2) Depending on the precast plank support and anchorage / connection, you SHOULDN'T have GREAT, if any concern regarding topping / concrete breakout / spalling / etc. I WOULD, however be MORE concerned about cracking or spalling on the top of the topping if you choose to pursue the "loose" rebar in topping.

!!!) HOW is the precast plank supported??? I do NOT see any support?

 

[BSVBD]

The "8" wide (nom) column", as you stated APPEARS to be a continuous wall.

NOW I see the the "NOTCH" and "BEARING" notes, on your detail, that makes me understand that the precast is bearing on the concrete wall. My oversight!

How are you anchoring precast plank ends to concrete wall? Dowels? Weld plates?

 

[dold]

OP, why not just put an embed in the top of the column/beam and weld the column to that? Unless your HC planks have to go in before the column. Then you'd be limited on access for welding to the embed. I know that you limit construction tolerances but that's just something the contractor will have to deal with. What's the column supporting, i.e. how many floors and how tall is the column?

Or, depending on the actual weight of the column you might be able to classify it as a post and forget about the OSHA deal. I think the limit is 300 lbs.

And damn, 8"x8" conc column...why so small?

 

[struct_eeyore]

For h/c anchorage, I've got #4 dowels hooked into the topped/grouted keyway.

My previous requests for embed plates in hollowcore have been in vain - due to the construction boom here in Florida, pre-cast manufacturers have more business than they want, and just tell us to f#%* off with custom requests. Wouldn't hurt to try again, I suppose.

Would a flat bar welded to column and mechanically fastened to the h/c really be a better solution? I'm curious to hear other opinions. I would think after the topping is in place, it would be just about as rigid as the welded rebar, in terms of inducing cracking.

 

[Eng16080]

1) I'm thinking that providing rebar welded to column face and embedded in the h/c topping is sufficient to satisfy the OSHA (4) bolt requirement - no?

I would say no. My understanding is that the 4 bolts are required for safety while the steel is being erected, meaning that the column needs 4 bolts to connect to as soon as it's lowered into place. At that point in time, the topping won't be poured. As mentioned above, maybe you only need 2 if the column is less than 300 lbs. There might be additional criteria to that as well.

I assume there's an 8" concrete beam going into the page flush with the top of the concrete column. If that's the case, can you lengthen the base plate (extending beyond the column faces) such that you now have space for 4 bolts?

 

[struct_eeyore]

dold - Sorry about the confusion - the column is 8" wide, but 24" deep, so there's plenty of room for the base plate. The steel column is supporting a single floor - 288sq.ft of trib with ~220 psf dl+ll. The concrete col. below collects ~ the same amount.

Eng - I suspect the 4 bolt requirement has to do with providing a nominal moment connection at the base - if we add another set of bolts in line with the other, I think the intent of the requirement is missed. Now I'm thinking to add a note that the column shall be fully braced until topping is cured.

 

[Eng16080]

I would definitely have 4 bolts, even if they have to be in line. It would still be twice as strong as 2 in terms of the column tipping over and would presumably satisfy OSHA. What are you going to tell them if they happen to show up at the site and only see 2 bolts?

Aside from that, I find it odd that the anchor bolts can only be placed along the center of the beam/column.

 

[jreit]

Could you weld an angle to the HSS and install the outstanding leg to the top of the hollocore plank? It's a more robust connection than the welded flat bar option and would help with bracing prior to pouring the topping. Might have to use galvanized/stainless steel and hardware to ensure service life of the detail.