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Seismic restraint of interior finishes
2

Seismic restraint of interior finishes

Seismic restraint of interior finishes

(OP)
For those in seismic critical zones:
What are you typically specifying/seeing for structural restraint of "interior finishes" to concrete floor slabs?

Where "interior finishes" can refer to:
-lights
-T-bar grid hangers
-other miscellaneous hanging light interior equipment

We have our usual preferences for R/C slabs, but have come across a P/T slab that we potentially have 1" of depth that we can safely drill into. Building inspector said Tap-con screws have been used, but my understanding is that screw anchors aren't codified. Also wondering "how to anchor" with such little depth.

RE: Seismic restraint of interior finishes

1" of depth to fasten is not enough to properly fasten anything. Have the GC mark out where the tendons are, then let the guy with the drill know where he can safely drill and fasten.

For overhead suspended fixtures, only epoxy bedded fasteners are appropriate IMO

there may be another way, such as suspending the lights/Tbar security cables from a properly set up cabletray type arrangement that is fixed to columns etc

RE: Seismic restraint of interior finishes

I like Hilti HDI-P. 400 lbs allowable @ 3/4" embed. The catch is that they're only for uncracked concrete. Given that they're pretty much designed for prestressed plank, I'd feel pretty good about saying their fine for PT slab for most applications as well.


RE: Seismic restraint of interior finishes

Would ideally use a cast-in insert such as the Hilti HCI-WF where supports can be located with a reasonable degree of accuracy or loads exceed the capacity of drop-in anchors. For post-installed shallow anchors we’ve switched from Hilti HDI-P to Dewalt Mini-Undercut+ as it’s the only shallow embedment anchor that has code report approval for seismic loads in cracked concrete that I’m aware of. For post-installed applications with heavier loads we use expansion anchors and x-ray the slab to avoid tendons.

RE: Seismic restraint of interior finishes

I agree. Deker's anchor seems like the cat's meow for this situation and I'll be moving in that direction myself.

RE: Seismic restraint of interior finishes

Interesting product. I don't think I've ever seen a phi factor as low as 0.40 before... Looks like the design pullout capacity is in the neighborhood of 160 lbs.

RE: Seismic restraint of interior finishes

...and at the mercy of the contractor/subcontractor not over-drilling these shallow anchors and damaging strands.

I have repaired many tendons due to over-drilling of such anchors. Subcontractors are always in denial that they drilled/damaged the strands - and after repair are made the GC typically back-charges the sub who did the damage.

If the contractor does NOT scan the underside of slab for PT tendon locations, I recommend that they keep all drilled fasteners away from the mid-1/3rd span of such slabs.

RE: Seismic restraint of interior finishes

(OP)
Yep, agreed. It would be kind of silly not to scan for the tendons. Avoids some hard-to-fix potential damage.

Thanks for the heads up on the HDI-P and Mini-Undercut. Those must be so new that THIS revised bulletin issued in 2017 still does not recognize their use even with the ESR having IBC 2018 (not the governing code up here, though).

RE: Seismic restraint of interior finishes

The drill bit has a shoulder stop, so assuming they use it that should eliminate most of the risk of over drilling. What raised my eyebrow a little is the max torque you can apply after the insert is set: 5 ft-lbs. I could easily see a worker exceeding that when tightening up a nut with a wrench. What happens to the anchor capacity if it gets over torqued?

RE: Seismic restraint of interior finishes

Nobody likes Hilti anymore... :) The mini-undercut is not a drop-in but as the name states it is an undercut anchor.

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