wedge anchor lengths for 2-post lift

[tff]

I just ordered a Rotary SPO10 2-post lift. (Looking forward to it). It comes with wedge anchors 5 1/2" in length, that I think will embed into the slab to a depth of about 4" or so.
Where the posts are I had the slab poured thicker...~8" thick. And my concrete is 4000 psi with wire mesh.
I suggested to my installer to go with longer anchors (the next step up is 7"). He did not recommend it, mainly because it's not needed (he's never installed one that has come loose).
Should I go with longer anchors, is it just a waste of money, or is there actually a downside of longer anchors (somehow related to spacing vs length)?
Any advice welcome. Thanks.

 

[finn]

Just curious, but why would you follow the advice of some random and anonymous person on the internet over the recommendations of the manufacturer, who employs degreed and certified engineers to design and qualify the product?

 

[Lucid Moments]

I have never heard of any lift actually coming out. So I am prone to say that longer anchors are completely unnecessary. I am not saying it has never happened, but I would bet a lot of money that if it has it was due to gross negligence on the part of the operator, the installer, or both.

 

[Kaizen]

Interesting question. Don’t think it would matter if the concrete was good all the way through. I’d use the manufacturers anchors in case anything ever did happen


Sent from my iPhone using Tapatalk

 

[Lucid Moments]

Just curious, but why would you follow the advice of some random and anonymous person on the internet over the recommendations of the manufacturer, who employs degreed and certified engineers to design and qualify the product?

I will say with regards to this that cost is one of the factors the engineers have to consider. If you take the cost out of the equation, or change how it fits into the equation, who is to say what the engineers might specify.

 

[mrobins297aaa]

your over thinking this

 

[tff]

I will say with regards to this that cost is one of the factors the engineers have to consider. If you take the cost out of the equation, or change how it fits into the equation, who is to say what the engineers might specify.

Agree. And the lift manufacturer wants to maximize their market and so they wouldn’t want to require a slab thickness more than absolutely needed.

Just to be clear, I’m not questioning the safety of the lift design with the supplied anchors. Just asking if there is additional safety margin with longer anchors or perhaps I’m missing something that would make it worse (due to bolt spacing). $50 to me for longer anchors if it’s better may be worth the piece of mind.

 

[JeepJohn62]

I’m going to suggest yes. If you have 8” of slab, why not use it? A 4” slab is a minimum and the 5-1/2 anchors are intended for that. Sometimes a shorter anchor will slip upward a bit and reduce the holding strength. Why not use all the concrete you have available? No one complains that their lift is too solid.

 

[FTG-05]

Agree. And the lift manufacturer wants to maximize their market and so they wouldn’t want to require a slab thickness more than absolutely needed.

Just to be clear, I’m not questioning the safety of the lift design with the supplied anchors. Just asking if there is additional safety margin with longer anchors or perhaps I’m missing something that would make it worse (due to bolt spacing). $50 to me for longer anchors if it’s better may be worth the piece of mind.

I would go to the Hilti site and look at their tech info. The last time I was there (several months ago) they had .pdfs that showed the minimum spacing between anchors.

The 5 1/2" anchors might meet the current spacing requirements of the lift base, while longer ones do not.

If in doubt, stick with OEM recommendations.

Good luck!

 

[GMCGarage]

I just ordered a Rotary SPO10 2-post lift. (Looking forward to it). It comes with wedge anchors 5 1/2" in length, that I think will embed into the slab to a depth of about 4" or so.
Where the posts are I had the slab poured thicker...~8" thick. And my concrete is 4000 psi with wire mesh.
I suggested to my installer to go with longer anchors (the next step up is 7"). He did not recommend it, mainly because it's not needed (he's never installed one that has come loose).
Should I go with longer anchors, is it just a waste of money, or is there actually a downside of longer anchors (somehow related to spacing vs length)?
Any advice welcome. Thanks.

You might go with a longer anchor, but it does not mean everything else is designed to that capacity. Who knows, maybe the base plate is the weak link, and no matter if you anchored it to China, the lift would still fail due to the base plate. Follow their install recommendations, save your money.

 

[finn]

You might go with a longer anchor, but it does not mean everything else is designed to that capacity. Who knows, maybe the base plate is the weak link, and no matter if you anchored it to China, the lift would still fail due to the base plate. Follow their install recommendations, save your money.

Exactly how I see it.

Unless you are going to do a structural analysis with a complete fumes and finite element analysis, modification of the manufacturer’s spec is hit or miss.

This isn’t 1960 anymore where things are designed by the seat of the pants methodology.

At least I hope that’s not how a reputable company like Rotary does things.

 

[matt_i]

Exactly how I see it.

Unless you are going to do a structural analysis with a complete fumes and finite element analysis, modification of the manufacturer’s spec is hit or miss.

This isn’t 1960 anymore where things are designed by the seat of the pants methodology.

At least I hope that’s not how a reputable company like Rotary does things.

These things are designed for minimum cost of install plus any possible lawsuits.

I always post how far superior a properly installed epoxied anchor is vs. a wedge anchor if you care about engineering fundamentals.

However if you're worried a brainless installer is going to epoxy the threaded rod to the dust on the drilled hole because they didn't blow it out thoroughly during prep, then you just keep upsizing the wedge anchor and minimum concrete thickness until no brain is required. This avoids cost on lawsuits which is far far greater.

 

[finn]

These things are designed for minimum cost of install plus any possible lawsuits.

I always post how far superior a properly installed epoxied anchor is vs. a wedge anchor if you care about engineering fundamentals.

However if you're worried a brainless installer is going to epoxy the threaded rod to the dust on the drilled hole because they didn't blow it out thoroughly during prep, then you just keep upsizing the wedge anchor and minimum concrete thickness until no brain is required. This avoids cost on lawsuits which is far far greater.

I would assume Rotary considered the epoxy fastening system in their analysis and, like most other lift manufacturers, declined to recommend it. I used them and like them, but I suspect the installation is not as robust as the wedge anchors for the reasons you stated.

An engineering fmea would identify the dust issue as a possible failure mode that would be difficult to detect by an installer. There are a lot of considerations to account for when designing things, especially when failure can yield catastrophic results.

It’s not prudent to go into the courtroom with your defense being that the failure was caused because the installer was a *******, especially when other, more robust designs are available. That’s bad engineering practice.

 

[sberry]

I have seen them used on the outside.

 

[mcbane]

If the bolt pattern is relatively tight, there is not much advantage using deeper wedge anchors. The pullout strength has to do with the size of the piece of concrete that comes out of the floor if the bolts pull out. And with a tight bolt pattern the pullout cones of individual bolts are already overlapping, so there is only a minor increase in the overall size of the pullout cone.

And epoxy anchor systems are a no win for lift manufacturers . For any permitted installation, even if you plan to do it right you must spend several hundred dollars to hire a special inspector who will watch and make sure you blew the dust out of the holes and used the correct amount of epoxy. And where no permit is required, no manufacturer wants the liability if some knucklehead saves money by using one bolt worth of epoxy for a dozen bolts.


Sent from my iPhone using Tapatalk

 

[wssix99]

And the lift manufacturer wants to maximize their market and so they wouldn’t want to require a slab thickness more than absolutely needed.

There's no pay-off to having a slab thicker than one needs. It's just a waste of money.

There are other considerations to a thicker slab that cause problems... For every additional unit of thickness, the reinforcing (mesh, rebar, whatever) is less effective. So, getting a "better" slab isn't as simple as just adding more concrete.

Thickening the slab, locally, can also induce cracking around a lift. (see below)

Just to be clear, I’m not questioning the safety of the lift design with the supplied anchors. Just asking if there is additional safety margin with longer anchors or perhaps I’m missing something that would make it worse (due to bolt spacing). $50 to me for longer anchors if it’s better may be worth the piece of mind.

In general, deeper anchors are not "stronger" but they will allow the slab to resist a greater pull-out force because the stress cones will be larger. Here is a thread with a discussion on those cones: https://www.garagejournal.com/forum/showthread.php?t=417532&highlight=stress+cone

but...

If the bolt pattern is relatively tight, there is not much advantage using deeper wedge anchors. The pullout strength has to do with the size of the piece of concrete that comes out of the floor if the bolts pull out. And with a tight bolt pattern the pullout cones of individual bolts are already overlapping, so there is only a minor increase in the overall size of the pullout cone.

This is a great point. If one goes deeper for a lift, the stress cones will overlap, which would cancel the benefit from the deeper anchors. It would just be wasted money.

BTW - If a load is so unbalanced that the pull-out forces are larger than designed, than the operator has probably really screwed up.

And epoxy anchor systems are a no win for lift manufacturers . For any permitted installation, even if you plan to do it right you must spend several hundred dollars to hire a special inspector who will watch and make sure you blew the dust out of the holes and used the correct amount of epoxy. And where no permit is required, no manufacturer wants the liability if some knucklehead saves money by using one bolt worth of epoxy for a dozen bolts.

+1 The thread above shows a picture towards the end of how an improperly installed epoxy anchor develops much less strength than a normal anchor.

Where the posts are I had the slab poured thicker...~8" thick. And my concrete is 4000 psi with wire mesh.

This can cause problems for the concrete. At this thickened section, there are greater shrinkage stresses per unit of reinforcing than in the thinner section. Where the two meet, differential stresses build up and cracks can form. (This is why there are no references to this type of pour in the lift instructions.)

Before the lift is installed, I would make sure there is a proper 30 day cure on the concrete, and then wet the floor to see if there are any hairline cracks around this thickened area. (I would also check this again after drilling the anchor holes for the lift.) If there are any cracks in these areas, then the lift may not be safe to use.

 

[GMCGarage]

These things are designed for minimum cost of install plus any possible lawsuits.

Thats what engineering is, to mitigate expensive construction costs and to minimize lawsuits.

If it meets code, the loads required, why do more? Unless the specifications call for higher loading, why would you design for it not to fall down x3 when x1.5 is adequate???

 

[firebirdparts]

If you have the depth it’s okay to use it. They just don’t want to make that a requirement and in my experience they did say use the supplied anchors. My lift is on the second floor so I chose to drill all the way through and put a few selected bolts into the basement but they would not like to have to approve that.

 

[firebirdparts]

BTW - If a load is so unbalanced that the pull-out forces are larger than designed, than the operator has probably really screwed up.
.

This is obviously true, but I think unfruitful. The pull-out forces are supposed to be huge, as designed, as properly loaded. They are huge.

People come in here every week looking to install a lift that don't understand that there are any pull out forces at all. It worries me.

Farther up somebody said they never saw one pull out, but if you google pictures of lift failures, you will see some.

If you are afraid of the lift pulling out, then you will make wise choices based on that fear in my opinion.

 

[JeepJohn62]

Check the Hilti website or other Manufacturers. They clearly document that deeper anchors provide greater pull out force. The depth increases the amount of concrete in tension. The concrete is the weak point in the system.

The recommended spacing is 10 times the diameter. So a 3/4” anchor should have 7-1/2” spacing. Even if the stress cones intersect slightly, you are still gaining strength.

The standard 5-1/2” anchors with a minimum 3-1/8 embedment provide plenty of strength with a safety margin. However, they repeat warnings about too much thread at the top, which indicates the anchor has creeped up in the hole before it engages. The 5-1/2” anchor only allows about a 1/2” creep before it fails the minimum depth, depending on the baseplate thickness. If you shim for leveling, you are losing more depth again. I currently have this issue with mine and wish I had a deeper anchor margin.

If I had a deeper slab, I would use a longer anchor for good measure.

Best wishes.

 

[tff]

A lot of good discussion. I've decided I'm going to go with what Rotary supplies and what my lift installer recommends... and that is the standard 5 1/2" anchors.