Plate embeds in precast concrete treads

[Ryan Nave]

I am working a project where we have to weld handrails into a precast concrete stair tread. I understand there needs to be a gap for heat expansion but spaces of 1/4" or more seems excessive to me. We are a metals fabrication shop and new to working with precast. Any assistance in verifying or refuting this would be appreciated.

 

[rowingengineer]

The math can be done, assume a 250 deg increase in temp of plate due to welding. Steel thermal coefficient let assume 7.2 x 10-6 but you could go for 11 X 10-6 if stainless.

Movement is 250x7.2x10-6xlength of plate. Will be less than 1/4 inch.

The 250 is for steel that doesn't have concrete behind acting as a heat sink so should be conservative.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[KootK]

Do these gaps even work? I'd have thought that you'd just be pushing the expansion forces through the tops of your headed studs no matter what you do with the gaps.

 

[rowingengineer]

KK assuming it is a 100mm wide it would be roughly 0.3mm of movement, given the shrinkage of the concrete around the plate during manufacture, it is unlikely that it would be an issue if the gap wasn't installed.

Looks like a nice place for water to sit against a plate however.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[dik]

I've never considered a gap...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Settingsun]

I did see spalling/cracking once but on a much larger plate and larger welds than for a handrail. Two more had already been cast by that time. The solution for those was painfully slow welding to control expansion. The remainder were given a gap. No problems with the studs on those but I'm not sure whether it was better confinement as the studs are somewhat interior rather than right at the surface, or whether the welders were still being cautious. No water problem due to orientation.

 

[KootK]

In large plates, I've seen a couple of instances of the headed studs shearing off of the plate to due expansion issues. For big ones, I'll now sometimes split them into several smaller plates with gaps in between. That does create some analytical problems of its own however.