Concrete anchors

[WinterDeere]

I am looking to set some drop-in achors as deep as possible in a 5" thick decorative concrete slab, for the propose of mounting the base plate of a large cantilever umbrella. The mounting plate is drilled for 3/8" hardware, which would be plenty strong, except that all of the 3/8" stainless drop-in anchors I find are only 1-9/16" long. I'm worried that any anchor set so shallow in this high-aggregate decorative concrete could tear out and leave a large divot in the concrete under high wind load.

Does anyone make a nice 4" or 5" long drop-in stainless anchor?

Yes, I know there are stud anchors that are longer, and would hold deeper into the concrete. But I don't want several studs left standing out of the concrete any time I move or remove the umbrella base.

 

[otlski]

So it seems your main concern is that your decretive concrete is not say 3000 psi but something weaker? Correct? Otherwise, the load rating would be valid and you would not have to worry.

Two alternatives perhaps. One, use epoxy anchors to spread the shear load more intimately. Two, go up two sizes in anchor bolt size and Loctite in a threaded insert.

 

[caver]

May not be what you want but I was supplied with Simpson Strong-Tie Titen HD 1/2 x 6" for the brackets on my timber frame. I'm sold on their product. I put them in with a 1/2" impact and never stripped one out.

 

[4570Man]

You could epoxy in all thread or set wedge anchors but these concrete screws are my preferred method.

 

[Dryland Farmer]

The concrete screws hold better than a wedge anchor. Keep in mind if you do use them and you screw them in and out often enough in the same hole, they will start holding less and less because it wears the sides of the hole. If you need to take them out often a threaded insert is your best option.

 

[EddieWalker]

I use galvanized wedge anchors for everything. I've never tried the screw in ones since I've had such good luck with what I'm familiar with.

https://www.lowes.com/pd/Red-Head-10-Pack-5-1-2-in-x-1-2-in-Wedge-Anchors/1000775748

One of my biggest issues with stainless steel is how week the threads are. I've stripped the threads while tightening stainless steel bolts just about every time I've used them. I'm at the point that I just throw them away and use galvanized bolts instead.

 

[WinterDeere]

yep, Dryland Farmer nailed it, the concrete screws are more a once-and-done solution. I don't think I'll be moving this thing often, but I like keeping the option open to remove it at least occasionally, if possible.

I'm leaning toward buying the usual 1-9/16" drop-in anchors for 3/8" bolts, but just drilling and setting them deeper. So, I might have to make my own longer setting tool, that's not a huge obstacle. I can drop a plain un-threaded sleeve in on top of the anchor, to prevent the bolt from wobbling in the drill hole, that could even be epoxied in place.

otlski named the problem correctly, I'm not sure what the cohesive strength of this exposed-aggregate concrete really is. There's a very high amount of aggregate, and it's smooth pebble to boot, so I'm guessing the cohesive tear-out strength is probably quite low. I think any shallow-set anchor is likely to just pull a nice 6" round divot out of the concrete surface, as it's torn out by high wind load on the umbrella. Getting the expansion sleeve set as far down into the slab as practical is my goal.

 

[WinterDeere]

I use galvanized wedge anchors for everything. I've never tried the screw in ones since I've had such good luck with what I'm familiar with.

https://www.lowes.com/pd/Red-Head-10-Pack-5-1-2-in-x-1-2-in-Wedge-Anchors/1000775748

One of my biggest issues with stainless steel is how week the threads are. I've stripped the threads while tightening stainless steel bolts just about every time I've used them. I'm at the point that I just throw them away and use galvanized bolts instead.

Your post came in as I was typing. These would work, in fact I have my shop compressor and pool pump equipment mounted using these. But they leave a stud standing out of the patio if the umbrella is ever moved or removed, and the only way to deal with that is permanent removal with a grinder. Not ideal.

As to stainless, I work with stainless hardware every day, for both work and hobby. From long experience, what you're describing is almost definitely thread galling due to heat, and not tensile failure. The UTS of 18-8 stainless is 70,000 psi, and the thread pull-out at 2 diameters typical thread engagement length is 47,500 lb. on a 3/8"-16 internal thread. You're not exeeding that, because the bolt tensile strength is only 5400 lb. on a 3/8"-16 UNC bolt.

Your issue is galling due to friction and heat while screwing it in on dry threads, made worse by load as fastener draws tight. Use antisieze, or really any form of thread lubrication, to resolve that issue. Dry galling aside, failures of threads in stainless simply cannot happen, as the bolt will always fail first (by 9:1 tensile force ratio).

 

[Dryland Farmer]

Your post came in as I was typing. These would work, in fact I have my shop compressor and pool pump equipment mounted using these. But they leave a stud standing out of the patio if the umbrella is ever moved or removed, and the only way to deal with that is permanent removal with a grinder. Not ideal.

As to stainless, I work with stainless hardware every day, for both work and hobby. From long experience, what you're describing is almost definitely thread galling due to heat, and not tensile failure. The UTS of 18-8 stainless is 70,000 psi, and the thread pull-out at 2 diameters typical thread engagement length is 47,500 lb. on a 3/8"-16 internal thread. You're not exeeding that, because the bolt tensile strength is only 5400 lb. on a 3/8"-16 UNC bolt.

Your issue is galling due to friction and heat while screwing it in on dry threads, made worse by load as fastener draws tight. Use antisieze, or really any form of thread lubrication, to resolve that issue. Dry galling aside, failures of threads in stainless simply cannot happen, as the bolt will always fail first (by 9:1 tensile force ratio).

Very interesting. I would have agreed with EddieWalker before I read your post.

 

[ponytug]

Your post came in as I was typing. These would work, in fact I have my shop compressor and pool pump equipment mounted using these. But they leave a stud standing out of the patio if the umbrella is ever moved or removed, and the only way to deal with that is permanent removal with a grinder. Not ideal.

As to stainless, I work with stainless hardware every day, for both work and hobby. From long experience, what you're describing is almost definitely thread galling due to heat, and not tensile failure. The UTS of 18-8 stainless is 70,000 psi, and the thread pull-out at 2 diameters typical thread engagement length is 47,500 lb. on a 3/8"-16 internal thread. You're not exeeding that, because the bolt tensile strength is only 5400 lb. on a 3/8"-16 UNC bolt.

Your issue is galling due to friction and heat while screwing it in on dry threads, made worse by load as fastener draws tight. Use antisieze, or really any form of thread lubrication, to resolve that issue. Dry galling aside, failures of threads in stainless simply cannot happen, as the bolt will always fail first (by 9:1 tensile force ratio).

I would have to agree with both you and @EddieWalker. While I know that stainless threads should not fail with anti-seize, and good ones don't in my experience. That said, I have experienced a rash of stainless failures that I put down to cheap stainless not being properly heat treated, or the alloy not actually being what was claimed. FWIW: I have reasonable success with fasteners from Fastenal, and McMaster, not so much from other box store vendors or online sellers, which is why I think it is a quality or specification issue.

All the best,

Peter

 

[WinterDeere]

Oh, yeah... there is definitely a huge range of "stainless" out there, especially now with Asian vendors flooding the market through Amazon.com and the like.

Even among legitimately-graded stainless, there's 18-8 (ANSI 304) versus 306 and others. You might use 306 underwater in a marine environment, giving up some strength, but 18-8 (304) for mounting a patio umbrella. Probably 99% of the hardware I stock is 18-8, made to ANSI 304 standard.

18-8 stainless is pretty close to grade 2 common hardware, in terms of ultimate tensile strength. Yeah, not the strongest stuff available, but you can usually up-size the bolt as needed to achieve the required tensile strength. The point was only that thread failures should not happen, the bolt should fail way before the thread, in a matched-materials situation with nearly any UN fastener system.

This was actually one of the design criteria 100 years ago for the "Unified National" fastener system we use today, that minimum thread pull out stregnth be something like 4x the corresponding fastener tensile strength. Their reasoning was that it is usually much easier and cheaper to extract the remnant of a broken bolt or stud, than to re-thread a female thread. So when properly used, the system almost gaurantees the fastener will fail before the female thread.

Things like galling between stainless fasteners can frustrate this system, but antisieze on the threads will almost always fix that problem.

 

[2manyrocks]

The other way to do this without any drilling is to use a heavy counterweight on the base.

 

[WinterDeere]

The other way to do this without any drilling is to use a heavy counterweight on the base.

That's what I have now. But it takes up more space, affecting how you can place chairs under it. Also, the metal base trapped under the counterweights is powdercoated steel, and leaves rust stains on the concrete. The anodized aluminum mounting plate that I'd use with these anchors resolves both issues.

 

[otlski]

We used epoxy anchor kits at Cape Kennedy to secure equipment in the old Shuttle processing facility. The concrete floor was allegedly 10 inches thick. No wonder too, our hammer drill went into it way faster than it ever should have. It was like hardened sand.

I see McMaster has some but I don't think that is what we used. I will look through my work emails for it.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[rumwrks]

https://www.lowes.com/pd/Red-Head-10-Pack-5-1-2-in-x-1-2-in-Wedge-Anchors/1000775748

Probably old fashioned but I prefer the hammer in lead insert anchors myself . I find they distribute the load more evenly over the concrete than the bottom wedge type.

Example: Bolt Depot - Woodscrew anchors, Lead, #6-#8 x 1"

 

[ponytug]

We used epoxy anchor kits at Cape Kennedy to secure equipment in the old Shuttle processing facility. The concrete floor was allegedly 10 inches thick. No wonder too, our hammer drill went into it way faster than it ever should have. It was like hardened sand.

I see McMaster has some but I don't think that is what we used. I will look through my work emails for it.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Sika Anchorflex?

All the best,

Peter

 

[sandman2234]

The other way to do this without any drilling is to use a heavy counterweight on the base.

That was my thoughts also!
David from jax

 

[EddieWalker]

Probably old fashioned but I prefer the hammer in lead insert anchors myself . I find they distribute the load more evenly over the concrete than the bottom wedge type.

Example: Bolt Depot - Woodscrew anchors, Lead, #6-#8 x 1"

I have a few of those in different sizes in my truck. I use them when attaching bigger things to brick, like gate hinges. I like them better than the plastic anchors, but I still use the plastic ones for smaller stuff.

 

[caver]

We used epoxy anchor kits at Cape Kennedy to secure equipment in the old Shuttle processing facility. The concrete floor was allegedly 10 inches thick. No wonder too, our hammer drill went into it way faster than it ever should have. It was like hardened sand.

I see McMaster has some but I don't think that is what we used. I will look through my work emails for it.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

For my timber frame the plans specified four galvanized 5/8" threaded rod at each corner. A backup tie down for storms. They supplied the Simpson tie down brackets but I had to buy the epoxy. They suggested Set XP. The downside is it was over $50 for the dual tube AND I had to buy a double barrel dispensing gun which wasn't cheap either.

 

[grsthegreat]

I only use the (simpson)Titan HD screw in anchors. Heck, they hold up the shelving of most pallet racking systems ive seen installed. But your right, there not ment to be continually removed and reinstalled in same hole. I use these to set generators to base concrete also.