Post-Installed Anchors - When to assume cracked vs. uncracked concrete

[BlastResistant]

Hi all,

Im reviewing a contractor's shop drawings for handrails. Structure is an existing 18 story hotel in Waikiki and all guardrails on the room balconies are being replaced. The contractor is showing use of proprietary expansion anchors that are not ICC approved for use in uncracked concrete. The contractor's handrail fabricator's engineer claims that the handrail baseplate anchorage locations on the existing concrete balcony decks are not located in tension zones so uncracked concrete assumption is ok. Our firm's policy is to always assumed cracked condition for this type of application, especially on existing structures.

Would you guys approve this anchor?

Thanks.

 

[Lion06]

I don't know. If you are sticking to IBC 2006 which requires code approved anchors, I probably wouldn't. I never assume uncracked concrete, ever. It's just a bad idea.

Additionally, if you are the EOR, you should be telling him to assume cracked or not. I don't think the comment, "it's not in a tension zone" is sufficient.

 

[slickdeals]

The existing balcony deck is probably a cantilever and ask him to prove that the top face of the deck is not in tension.

 

[hokie66]

If it is not in tension now, it will be after the installation of expansion anchors.

 

[JoshPlumSE]

If's its in the top surface of a cantilevered slab, then I would call it the tension zone and require the cracked concrete calculations.

I agree with slickdeals. Explain to him that the top surface of a cantilever is almost the definition of a tension zone.

If he disagrees, then ask him to explain to you the code basis for referring to it as something else.

 

[BAretired]

Definitely, assume the cracked condition in the top of a cantilevered balcony. It seems difficult to argue otherwise.

If you require someone to oversee the work in Waikiki, I would be pleased to proffer a proposal.

BA

 

[weab]

Everyone,

I have been to hotels and condos that had balconies with columns or walls in the corners of the balcony - not a cantilever. So perhaps in this case, it is not a cantilever.

I don't have a problem assuming uncracked when that can be CLEARLY established. However, even if this balcony is supported in the corners, there could be slight fixity near the supports, that is, negative moments and cracks. In the end, some anchors may be in cracked sections so I agree that cracked sections should be assumed.

 

[hokie66]

Don't forget that many cracks in concrete structures are due to restrained shrinkage rather than flexure. If it is a long building, some cracking across the short dimension is almost inevitable.