Design Considerations for Thermal Break at Outrigger Embed 1

[efFeb]

Hi!
I have been asked to add thermal breaks at steel outrigger members, where they connect to the base concrete structure as shown:

I have tried out Hilti Profis's calculation for plate with stand-off and would need to increase the bolt size to meet their criteria for bolt bending. I have also looked at some structural thermal break products and find that the modulus of elasticity is similar to that of steel. With this being the case, am I being too conservative by checking for this stand-off distance? Does anyone have thoughts on this or a recommended product from a similar experience?
Thanks so much!

 

[r13]

Unless you are able to analysis structure with composite base plate assembly, I think you are fine.

 

[dik]

I've done this numerous times with headed studs as well as steel framing backup... going through insulated metal walls for pipe supports, cable tray supports, etc. I usually use a product made by Fabreeka or Tyvar 1000 for the thermal break. I've no business interests with either firm. Used to use HDPE way back.


Dik

 

[KootK]

@OP: are you casting this whole thing into the concrete as one prefabricated assembly? Normally, I see the outrigger and plate bolted on after the slab is cast.

I have also looked at some structural thermal break products and find that the modulus of elasticity is similar to that of steel.

I think that I see where you're headed with that. Can one make the argument that it's essentially a bolt shim as with regular steel to steel joints? I would say no. The bolt shim thing relies on the bolt being able to rotate into a position where you develop kind of a strut and tie system with the bolt taking primarily tension. Here, because of the embedment into concrete, you won't have that regardless of the stiffness of the thermal break stuff.

Does anyone have thoughts on this or a recommended product from a similar experience?

A method that I've used that is, admittedly, a little bit sketchy is shown below. Caveat emptor.

I have been asked to add thermal breaks at steel outrigger members, where they connect to the base concrete structure as shown:

With the bolts passing through the thermal break un-isolated from the other steel hardware this really won't be a very effective thermal break. Sometimes it's best not to tell architects this stuff though. It tends to only slow down the work and make your own life harder. I know... I'm a horrible person.

 

[KootK]

 

[efFeb]

Thanks for your help everyone!

 

[dik]

Often the heated mass of the steel structure on the inside keeps the nuts from frosting... albeit there is still some heat loss.

Dik