Hollow-Core Plank - Welding Along Length

[jack36]

I have a project with hollow-core planks bearing on structural steel framing. 8" hollow-core with 2" normal weight topping. I have specified the planks must be supplied with embedded plates to allow for welding to the top flange of the steel beams. I'm requiring this where the planks bear on the steel and also when the plank is parallel to the beam span. The plank manufacturer is stating they "do not recommend welding along the length of the plank because it does not allow for vertical movement due to volumetric changes, and may result in cracking."

I have not seen this in the past. Does anyone have experience with this condition? I need the planks to brace the top flange, and I thought this was the standard method.

 

[KootK]

1) For planks bearing on the beam, precasters have directed me to weld only every second plank to the beam for similar reasons. Alternate planks get welded at the other end if necessary. I'm not sure how free the planks are to adjust their volume once all of the topping etc is in place but it makes the precasters happy and allows me to get some beam bracing in.

2) For planks running parallel to your beam, the trick is probably to decouple axial movement in the plank from axial restraint provided by the beam. For beam bracing, perhaps you could used pairs of clip angle guides along the beam that are welded to the precast but not attached positively to the beam. That'll give you some beam bracing without the plank restraint.

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.

 

[structSU10]

if you are getting into longer spans / higher prestress for the precast, the camber would be an issue with general fit-up at midspan anyway. What does the beam in line with the plank do?

 

[jack36]

Thanks for the feedback. The beams running parallel with the planks are used to support other beams in the opposite direction. I've got some open spaces to deal with that don't allow for convenient column locations.

I specified that shim plates be added as needed to fill the gap due to camber.

KootK: The angles are a good idea. I'm not sure I'm comfortable with there not being a connection between the beam flange and angles. I suppose it still provides the bracing as long as the angles are installed directly against the flange on each side.

 

[KootK]

For what it's worth, you see similar details in renovation applications often. These aren't my handiwork.

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.

 

[jack36]

Thanks KootK.

Another question for this condition: I have an interior braced frame that is parallel to the plank span. I planned on transferring the diaphragm forces with the embedded plates (4' o.c.). If I eliminate the embedded plates, I'm thinking my only option would be to have the hollow-core manufacturer leave a gap between planks at the steel beam so I could use welded studs. They would then obviously grout to fill the gap. Anyone have any alternatives to this?

 

[structSU10]

the gap with welded studs is basically what I have done in the past as well, but I made the infill be the concrete used for the topping slab, not just grout. I also extended the studs into the topping slab, so they were long.