Hilti Anchors

[Veer007]

Hey Guys,

Generally, In steel structure, where does the expansion anchors preferred, and where does the adhesive anchors preferred, then why?

Thanks in advance!!

 

[TheDirtPounder]

Hilti provides a nice anchor selector chart (Link) that might help specify best use for each style of anchor.

As for me, I generally only specify mechanical wedge anchors on very lightly loaded structures/equipment. For mechanical anchors there is generally no requirement to clean out the hole prior to anchor installation which can cut down on construction time if you are installing a mass amount of anchors. I prefer to use adhesive anchors whenever I can as I feel more comfortable with the performance of the connection.

Also, you need to review local jurisdiction requirements, some places won't allow anchorage of certain types.

 

[JedClampett]

I prefer epoxy in any situation where there might be a vibratory or varying load. The mechanical anchors crush a small mount of concrete and I worry that might progress. But that's just me.
Funny thing is, is that I worked on nuclear power plants for 20 years and we never used epoxy anchors. They weren't tested or they were worried the zoomies would change the epoxy properties. Now I'm about 80-20 epoxy.

 

[dik]

I prefer adhesive anchors also, but mechanical anchors are generally less costly and easier to install. If critical, I don't use mechanical anchors except occasionally for heavy loads, I've used Hilti HSL anchors. My preference for real loads is the Hilti Hit-Z or Hit-TZ.

Dik

 

[JoshPlumSE]

You do have to be careful with adhesive anchor selection for overhead application. So, mechanical anchors may be preferable in those conditions.

 

[dik]

Big Dig comes to mind... the adhesive was the problem, and Hit-Z or Hit-TZ would likely have worked... would have to look into it, before speccing it.

Dik

 

[skeletron]

The heirarchy for overhead anchors is: undercut --> expansion --> adhesive

One of the great ways to understand the limitations of the anchors is to install one yourself. My experience recently:
1. Downward position, expansion anchors. There's a lot of dust that needs to be cleaned out. I also had no idea if I was torquing it enough, I just kind of got it snug and then put another 1/3 of a turn on the nut.
2. Overhead position: drilling with a hammer drill overhead is difficult. Keep this in mind when you spec out your anchor size.

Another good exercise is watching some of ACI's adhesive installer videos. They show the cut section of some "good" installations and how the epoxy doesn't necessarily get everywhere you think it does if you're not careful.

 

[Ingenuity]

Another good exercise is watching some of ACI's adhesive installer videos. They show the cut section of some "good" installations and how the epoxy doesn't necessarily get everywhere you think it does if you're not careful.

...I did the ACI adhesive anchor installer certification a few years back - theory (classroom) and practical (installation) - of a class of 11 experienced installers less than 50% passed the cert course. I asked ACI about pass/fail rate and they said 50% was about typical. I fortunately did pass both segments of the course.

 

[skeletron]

@Ingenuity: Yes, I've heard a similar number. It really was eye opening for me to watch the videos and learn about the installation requirements (I've never installed one). I used to spec them all the time thinking they were fail safe.

 

[Enhineyero]

From a buildings structure perspective

Chemical anchors
- used when fixings are near edges or spaced closely (50mm to 150mm spacing/edge distance), which is 95% of the time. Has relatively lower capacity than Mechanical Anchors (like by like comparison).
- can be used for wet environment

Mechanical anchors
- used when higher capacity, usually those that cannot be resisted by chemical anchors, is desiredd (large edge distances and spacing required)
- also preferred for overhead anchors.

 

[dik]

I would normally use undercut anchors for overhead use, but have used chemical; it depends on the circumstance. Mechanical anchors are generally less costly to install and are mostly used for this reason... also less fuss. Be aware of the bursting forces if near an edge. Some chemical anchors can be installed with minimal cleaning... I don't do that... full cleaning for all.

I also don't load anchors to their design capacity... typically about 70%. With anchors and columns, I tend to be a bit of a chickensh*t.

Dik

 

[Prestressed Guy]

I will be a heretic. I prefer to use neither. My anchor of choice is a concrete screw anchor such at the Titen-HD by Strong-Tie or the KWIK HUS EZ from Hilti. They have the greater load and lower edge and spacing distance possible with epoxy without the special inspection, creep, and temperature limitations.
If you are unfamiliar with them, think of a lag bolt for concrete.

 

[dik]

My first encounter with them, they were called 'Screw Bolts', a decade or two back, and they worked well. I still prefer the Hilti Hit-Z, myself... auger like wedge forces the epoxy against the side of the hole for grip.

Dik

 

[Ron]

Be careful with adhesive anchors in cold weather, particularly if loading or partial loading will occur quickly. Did a failure investigation a few years ago where columns in a PEMB were being set with adhesive anchors. It was cold (for Florida), with temperature overnight at about 26F. Warmed next day to about 40F. Anchors had been placed at around 35F and left overnight. Next day they were plumbing columns and one of the workers was kneeling between two columns to tighten a turnbuckle. His back was to the column that was being pulled. The anchors came out, the column fell and crushed the worker.

Yes...the manufacturer warns against this, but contractors are always more concerned about speed rather than following specifications or product directions.

 

[dik]

Cold... we don't need no stinkin' cold... not where I am. Worked on a project about a decade back and was on site... I stuck my pocketknife into the mortar joint and it was still plastic. I told the contractor to put some hoarding up and to heat it, and was informed that it was constructed the day before...

Dik

 

[Veer007]

Thanks for the info. guys...

Thanks in advance!!