Hammock Mounts in Masonry Wall

"...standard expanding masonry anchor, size 3/8" or 1/2"."

Like a DynaBolt?

Are the consequences of failure so dire that this precaution is necessary?

How high in the air is this hammock gonna be?

Failure could result in serious spinal injuries. A flat fall on concrete can break bones, snap a spine in my opinion.

There is the possibility two people will be in the hammock. My friend is from South America, where hammocks are shared. Two people can relax in a hammock by lying at right angles to the long way of the hammock, it's quite comfortable.

That's a lot of direct pull on a wall anchor. I'm trying to engineer some safety in here.

That dynabolt looks really good. I will try to find some, thanks.

The second (upper) anchor won't help much, and might even increase the stress on the lower one. This may depend on the specific angle that the rope leads away from the anchor toward the hammock.

One of these, with lead anchor, properly installed, will do...

http://www.fastenal.com/web/products/detail.ex?sku=42138

Somehow, I think mounting the two anchors side-by-side about two inches apart would do a better job of weight distribution. Just run the wire/rope through them both.

Something like this:I'm sure there are "eye nuts" too. 1/2 inch, for sure.

We use these to anchor bike racks, park benches and garbage cans in my fair city.

Not an endorsement.

Concrete Sleeve Anchor

Concrete Sleeve Anchors' design allows them to anchor into concrete, brick and block. Sleeve anchors work by inserting them into a hole drilled into concrete. Turning the nut pulls the working end of the sleeve anchor up through the sleeve, expanding and anchoring itself securely in the concrete, brick or block.

• Sleeve Anchor Technical Information
• Installation Video

I agree, side by side is the only way to go.

Two inches apart, isn't that close for expansion bolts?

Yes, it is.

We have always used a rule-of-thumb, and I did not know why, exactly, until I started researching after I saw Lyn's post about the anchors. In the data on Lyn's link for the anchors it says to space them about 10 times the bolt diameter from each other and 5 times the bolt diameter from an edge.

I've also seen the data sheets with the anchors and just gone by what they said.

SO - I know what to do. Passingtongreen probably can explain what happens when one anchor is expanding and "mashing" the concrete toward an adjacent anchor that is also "mashing" back at the other anchor. Since Moosie is here in Texas celebrating this weekend, I guess we have to wait for his explanation until he is back on line.

I think it has a lot to do with concrete's lousy tensile strength. If a 1/2" anchor were drilled 1" from a corner of a slab, I think we all know the concrete would flake right off. "Spall" is that right, passington? But I don't know so much about what happens in the middle of a giant tilt-up slab when there are many feet to the edge. But, I bet if I were to try to put six 1/2" anchors in a 2"x4" area (2" spacing) I'd have a bunch of shattered concrete or a big chunk with anchors in it that pops out of the face.

And I bet it also has a lot to do with the PSI of the concrete, although I am not going to guess which way the scale tips. On one hand, it seems the higher PSI would hold tighter, but it also shatters more easily, and the PSI compressive strength probably has little to do with the spacing... but now wait, I bet it does because the higher the PSI, the "harder" the anchor can mash against the wall of the hole. But, then the spacing comes right back into it.

What if it is Lousy Mob Concrete that was cured one day in the Texas heat and framed the next? What if it's fiber-entrained concrete that doesn't shatter as easily?

Enough. CR4 concrete expert opinion time...

Passington? Moosie? Others?

I think it is too. The anchor bolt design data gives derating factors based on bolt spacing, but if the spacing is wide enough there's no derating.

I certainly won't argue with anybody about the spacing.

I'm not sure of your statics. Assuming a 200lb load and an angle of 30 degrees to the horizontal, the force in the rope will be 200lb (200lb/2sides divided by sin30). 200lb down on the top hook and, 200lb acting 30 degrees above the horizontal on the lower hook.

Nothing gained because the pull on a single hook would be 200lb acting 30 degrees below the horizontal.

Now, I'd better go and do the math to make sure.

If it is solid concrete, you don't need a huge hook. Look up Hilti and see what they will do.

The way I figure it in my head, is if there was no upper hook, all the load would be on the lower hook. Any load transferred through the pulley on the lower hook to the upper hook has to be subtracted from the lower hook.

The lower hook is in tension, trying to pull it out of the wall. That's my concern, masonry can slowly fail as the hammock is rocked.

The upper hook is in shear, a good load for concrete in my opinion.

You haven't changed the tension on the bottom hook, you have reversed the shear on it and the shear on the upper bolt is approximately double what it would be if there was only one hook.

Do you know how much weight it would take to straighten out a 1/2" steel eye bolt?

I bow to your experience and knowledge....You are correct that it's about a 1000lbs....

http://www.hammocks.co.uk/hanging-a-hammock.htm

Use a welded eye?

One more thought Mike, can you bore all the way through the wall and through-bolt it with a plate (large washer) on both sides? That gets rid of your concern about the anchor wearing out the concrete.

Is it possible to drill right through the wall and use an ordinary bolt or threaded rod, with a good-sized plate on the far side? That way the only limit is the strength of the wall, not pull-out.

A 1/2" bolt should be ample, provided the 2 people in the hammock aren't doing anything too strenuous.

Just an idea: Is that Hammock really made for two people and rocking action?

You might get the anchor right just to fail on the ropes.

As said just an idea.

_{Buggers off still thinking about two people in a hammock and rocking action. Its weekend after all ...}

Epoxy is popular here with masonry anchors. I talked to my son, who is in engineering school, and he had a good recommendation. I am now seriously considering drilling my anchor hole at a downwards angle into the masonry, and using a long screw eye. I will run the screw eye all the way up to the wall for maximum support.

This is a 'tent peg' type of arrangement, so the masonry anchor is not being pulled out of the wall, but is under more of a side load.

I will see how one anchor does on each end of the hammock. If I see any sign of the eye bending or moving, I can easily double up and put two anchors and eyes on each end.

Thanks for the input, folks, I'll let you know how it goes.

"If I see any sign of the eye bending or moving,..."

You might do what I have done: Weld 'em shut before you install.

Can save you a lot of grief later. Firsthand experience.

I like it.

I agree with your disagreement.

Obviously the hole will not be drilled at 2° from the wall surface, but it doesn't follow from that there is no angle which gives optimum performance.

The fact that bending and shear stresses are increased (they are still there with 90° hole) isn't critical, as for a typical anchor the pull-out load is much lower than ultimate tensile load of the bolt material. And it's easy enough to calculate the bending and shear stresses to make sure they're OK. Of course you would make sure the point where the hammock ropes are attached is as close as practical to the wall surface, to minimise bending stress.

If I had to hang from something at a height and the choice was between an anchor in the underside of a flat concrete slab, and a similar one in a vertical wall I know which I'd prefer, whatever Hilti & co say.

My Dad did not exactly describe my idea as I thought of it, and his reasoning is sound as far as my training leads me to believe. Placing a bolt in concrete at 90° and tying off a hammock will put tension on it (with side loading at the angle of the rope). Placing the bolt at an angle changes some of that tension into compression, providing the anchor is buried deep enough, it will place the downward compression along the face of the wall (and outward). Pivoting at a point along the buried length the force will transition into an upward compression into the wall.

At the 90° the compression would be mainly from the fitting used to secure the bolt into the wall, the tension would be trying to pull that plug of compression out which is not a direction concrete is strong in.

As we know concrete is stronger in compression than tension.

The design I described to my Dad was similar to the picture below mounted on the wall instead of in the grass, and using only 3 lag bolts instead of the 9 pictured. This method would transfer some of the load to the second two bolts, it does reduce the pivoted compression forces directed upward by the inner section of the load carrying bolt though.

I provide this design and welcome criticism as the desired outcome is only a secure mount for the hammock. I will admit I have not taken a composite materials class as yet and my knowledge of the properties of concrete come from my own experience prior to college (I began college in my 30's so I do have substantial experience) and my studies thus far.

~A son Proud of his father~

Woops...forgot to include image.

~embarrassed!~

Good idea, as long as your plate is large enough to ensure the bolt holes don't damage the integrity of the wall by being too close together.

Drew k

http://www.us.hilti.com/holus/page/module/home/browse_main.jsf?lang=en&nodeId=-469912

If you have the skill and product available I would suggest adhesive or epoxy anchors.

I strongly recommend reviewing the literature on the Hilti site ffor an education on anchor placement, spacing, mechanical limitations, loadings, etc. You can download PDFs for future reference.

This is an endorsement, and no, I do not work for Hilti.

Don't like the rolled sleeve anchors, I have known the bolt to pull through because the hole wasn't spot on dimension wise.

Even the cast block wedge anchors require precise drilling to work best,and this assumes a solid substrate. If you hit rebar in your wall this is lost straight away, and its on to chemical anchors (which can be put closer together without derating)

cnc jim

I remember some years ago having been faced with the same problem:

I used 2 (4mm) steel plates (mild steel) with 2 chrome plated double hooks (12mm thread) fixed with nuts in the centre of the plates, and mounted each plate with 4 dyna bolt anchors tho the wall. (I hollowed the walls behind the plates to accommodate the nuts...!)The idea was that IF a bolt would 'give way' - it is unlikely that ALL 4 on one end would get loose at the same time... and I would most likely notice that in time - i e: NOT fall with the hammock and suffer any injuries.....

Even if dyna bolts are very reliable, NOTHING IS PERFECT and bricks do 'crumble' occasionally.....

Hope this helps

Kim

If you can determine the makeup of the wall & if indeed it is concrete and not cinder block then get the longest fixing you can, preferably to half way the thickness of the wall & of the expanding bolt type,this will make sure that you have the maximum weight above the fixing & keeping it in the centre of the thickness will avoid breaking out,you must also take into account the amount of wall above the anchor, if it isn't enough will the wall burst out upwards, so if everything is Ok then you should have many happy minuets oops days swinging in your hammock.

NB, Put a mattress underneath just in case.

Bazzer

If I was installing this for someone else, I would look at this like a fall protection anchor point and use OSHA's 5000 lb rule. Then at the link in post #35 , check with Hilti on what anchor they recommend.

For me a couple of 16 penny nails drove at the same time through a 1/4" drilled hole would do. I might put some pillow underneath just in case.

Why don't you just buy a hammock stand designed to hold a hammock instead of anchoring it to the wall?

Look up epoxie set concrete anchors. They are for solid and cracked concrete. These will eliminate the need for two anchors.These anchors are used in all sorts of industrial applications.

Drill the holes for your anchors on a downward slant, from 30 to 45 degrees.This will reduce pull-out stress, and transfer the weight to a shear force acting on the anchor bolt.Use a 1/2 inch(25mm) lag shield, with internal machine threads of 1/2 inch diameter.

Sleep well.

Well, for better or worse, I mounted the hangers like HiTekRedNek recommended. I will follow up after the epoxy sets and the hammock is hung. I told the owners to put a cushion under it just for safety. The hook is 3/8" steel, in the wall at about 30 degrees. They tell me only one person will be in the hammock, so that puts about 75 lbs. load on each hook. If I see the hook bending, I will drill it out and put in a 1/2" hook. I put masking tape on the wall to control the mess.

There is a problem that you don't see. The weight in the center is multiplied by the distance from the hooks. if you had a straight down load on on hook it would support the entire load but when you put the load in the center it is like a lever the load varies depending on the angle from the anchor point but it is multiplied by the distance.

I got stuck in a mud puddle while deer hunting, the bottom of the doors were below the mud. I happened to have about a hundred feet of log chain. I dug down until I was able to connect the chain. I hooked the other end to a tree that was almost a hundred feet away. I then went to the center of the chain and lifted as hard as I could. And by myself I was able to exert enough force to pull that truck out of the mud.

So you don't excerpt 75 pounds on the anchor but a multitude of that force!

Thats correct all good sailors use this method to tighten up the last bit of there sheet lines..

In my case I would have used a larger bolt, no calculation involved just good judgement. No sweat.

Thicker bolt and an eyebolt at that would have been better, I can see your hook bending down at the wall junction.

But thanks for following up with what you decided

cnc

I'm going to check the hook when I return next week to hang some pictures. If the hook is acting weak, I'll change it. The store did not have a larger one, I'll be checking other stores in the meantime.

I was hoping the hook might bend some, work harden a little, and settle down at that. I've seen plenty of hammocks hung on this size hook, but into wood where the load was all tension.

If the wall is not too thick, can you drill all the way through the wall and use a long eye bolt and a backing plate and nut. This would take care of any direct pull. Anchors work best when the load applied is 90° to the fastener axis. As the angle of pull goes from 90° to 0°, the pull-out force decreases. Some anchors are better than others.

Yeah, see my #16!

As the angle of pull goes from 90° to 0°, the pull-out force decreases. Some anchors are better than others.

__________________Dont you mean the reverse of this?

At 90°, there is no axial load, but as the angle changes from 89° to 0°. it requires less force to pull it out of the wall.

Ha yes the inscrutable English language.

I inferred that the pull out force increased as against the 90° position as there is no [relatively speaking] pull out force at 90°.

I understand where you are coming from I was looking at the description differently.

Ok guys,I really didn't see it going this far, but here is how we hang 10 inch diameter water line on a concrete wall.

We use an angle iron bracket, in the shape of a right triangle.The pipe is attached on top of the base of the triangle, with the adjacent side anchored to wall with 4 or more anchors, and the hypotenuse acting as a knee brace.We use closed eye bolts when movement is required due to expansion, etc.

A smaller version of this should suffice for two Sumo- sized people wrestling on the hammock.

Chose the size of the angle and hook according to your degree of paranoia concerning liability.

'nuff said.

I want to thank everyone for their replies on the thread. It really helped me in coming up with my design.

I wanted to hang my new hammock on my lania between two concrete posts. After successfully hanging it, I'm still not sure if they are solid block or cinder block (I think one each). A few quick facts about me: I weigh 225 lbs, 46 yrs old w/ a Purdue engineering degree, a dumb do-it-yourselfer not afraid to take risks and try & fail and I'm a tightwad (must be the Scottish roots - ha ha!).

So, I wanted a cheap solution that I could buy at Home Depot or Lowes and didn't want to wait on ordering special materials from the internet. I probably spent 2 hrs surfing the net look at all the great insights then about another 3-4 hrs at the stores thinking through many different solutions until I landed on this one (did I mention I was cheap?).

My solution costs $16 (plus $7 for a masonry drill bit I did not have) and should only take 1 hr to install (plus glue cure time if you need it like I did). Here is my supply list:

2 1/2" x 6" eye bolt w/ nut and 2 fender washers - $6

2 1/2" x 2" concrete drop-in anchors - $2

2 3/4" spring links (to hook between the eye bolt and the hammock eye - you may not even needs these or might have something already that could hook them together) - $8

1 5/8" x 6" masonry drill bit - $7

I drilled a 3" deep hole, cleaned out hole, put on nut, then washers then screwed on drop-in anchor until it was about ready to expand. Then I inserted it into the hole and started turning the eye bolt until it would not go any farther. I then tightened the nut up to the wall. The first one went in flawlessly. The second hole was hollow after 2" so I had to cut off 1.5" of the bolt and use Gorilla Glue in hole to ensure the anchor held. I let the glue dry overnight. I just tried it out today and seems to be very sturdy - woo hoo! This not an endorsement for this design however since it's only Day 1, but it feels very strong and I'm confident if it can hold me, it should be fine.

I hope this is helpful to you as you consider all the designs and info on this thread!

Welcome to CR4 jcbslb! I'm glad to hear about the success of your project. Thanks for sharing the photos!