Shallow embedded epoxy anchors 1

[Greenalleycat]

Hey all,

Epoxy anchors are all the rage these days and their performance seems to be getting better and better as time goes on.
One contractor that we work with does fall arrest installations and that naturally involves epoxying in M16 rods
Typically our standard spec has been 125mm as this has been the minimum allowed by the top epoxies (Hilti RE 500, Ramset C8 Xtrem etc)
Now these epoxies are allowing anchors to be embedded as shallow as 80mm in latest software iterations

Technically, these do meet our design loading requirements, although I am awaiting a response from a manufacturer about whether there are any concerns with impulse loading vs static loading
I have some concerns about the redundancy of shallow-embedded epoxy anchors - potential poor floating leading to delamination of cover concrete and so on
I've said to the contractor we are unlikely to use it for any retrofit work on old buildings due to the many unknowns, but that we will look into it for newer buildings where concrete thickness, reinforcement content, and build quality can be more confidently assessed

I'm now in that process of doing some due diligence, so I've emailed off to some tech support people at one epoxy supplier
However, I'm interested to know whether anyone else has ever used shallow embedded epoxy anchors in such an installation - any thoughts to share?

 

[Just Some Nerd]

For my part I'm not particularly comfortable with trying to max out the capacity of any epoxy solutions. I prefer to specify as much embedment as possible given the concrete's thickness, unless said thickness is significantly greater than what is required for design loads + a good chunk of headroom. My trust in terms of proper installation is quite low when it comes to epoxy solutions these days - my team had a situation once where the epoxy wasn't actually applied to the inside of the hole, found that out the hard way seeing bars that pulled out squeaky clean, naturally the stairs they were attached to fell down.

I'd say I'm fairly confident in the products themselves, but that's almost never the problem after all. For peace of mind I would stick to that 125mm minimum as I wouldn't be in any rush to save them 45mm of drilling

 

[hokie66]

For 'Just Some Nerd', that is common sense advice.

 

[human909]

However, I'm interested to know whether anyone else has ever used shallow embedded epoxy anchors in such an installation - any thoughts to share

Thousands of rock climbers from around the world have been doing this for decades. Suitably installed anchors are MORE than capable if loaded in shear. 80mm is not at all shallow for shear loading and normally should be fine in tensile loading. This is all tried and tested by 'amateurs' in the rock climbing community. And of course plenty of tests by the professionals. A quick google can find dozens of videos online on this.

If you are looking at tensile loading for a well installed anchor then at 80mm you might also start to wonder about the quality of the substrate rather than the epoxy.

For a poorly installed epoxy anchor all bets are off. If you epoxy is sticking to the drill dust and not the hole then things aren't looking good.

I am awaiting a response from a manufacturer about whether there are any concerns with impulse loading vs static loading

An "impulse" loading of a force 24kN is going less severe than a static loading of 24kN. So you don't have much to worry about here. After all, this question translates to; is 0.1s of 24kN worse than 50 years of 24kN. I think the answer should be obvious.

we will look into it for newer buildings where concrete thickness, reinforcement content, and build quality can be more confidently assessed

If that was the case then I would have no hesitation relying on only 80mm embedment IF performed by suitably trained installers. Seriously, these installs have safety factor upon safety factor upon safety factor on them.