How much load is going through the bolts

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In summary, the man is asking for advice on using bolts for a squat rack. The man attached a picture of the bolt setup he is using and explained the lines he used. The white circles are M16 bolts, the red arrow is a pivot point, the yellow line is 880mm long, the pivot point to load, and the blue line is 1000mm long. A barbell sits inside the green slings. The man squats up to 500kg, and the bar could fall a maximum of 1000mm. The man asks if 2x M16 bolts are big enough.
  • #1
Stickyman
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Hey guys.

Im building a special type of squat rack for my gym, and need some input on the bolts to use.

I have used high tensile M16 bolts on all joints, but am not sure if it is enough, hence me joining this forum and asking you guys.

Attached is a picture, and Ill explain the lines I've used it a bit more detail.

The white circles are M16 bolts.

The red arrow is a pivot point.

The yellow line is 880mm long, the pivot point to load.

The blue line is 1000mm long.
A Barbell sits inside the green slings. You squat up to 500kg, the bar could fall a maximum of 1000mm.

IMG_8749_zps2c267299.png
So, the question is;
If a weight of 500kg falls inside the slings, which is 880mm away from teh pivot point, how many kilograms of force will be on the 2 bolts at the pivot point? Is 2x M16 bolts big enough?

Many thanks for your time.
 
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  • #3
The answer to your question requires knowing how long it takes the falling mass to stop. That is determined by the flexibility of the structure.

If the structure has no flexibility and the falling load stops instantaneously, then the force on the bolts will be infinite.
 
  • #4
The link in my 2nd post has the video of my dropping the bar with 400lb from about 1m height.
 
  • #5
Then you can measure how long the mass takes to fall and how long it takes to stop.
I cannot access facebook and I avoid watching videos.
 
  • #6
I think you need some professional advice for designing this, since obviously a falling 500kg weight could cause a serious injury to the user.

As Baluncore implied, the force on the bolts will depend very much on how flexible the green (fabric?) slings are. Beyond that comment, IMO you need to do some proper calculations based on the full details of the structure, not just a photo and a couple of dimensions. Personally, I wouldn't like to guess if the bolts or something else would fail, and it would be a guess from the (lack of) information we have.

You could easily be talking about seriously high loads here. The multiplication factor from stopping the falling mass could easily be 10 or 20 times. Them you have a lever arm with a ratio that look like about 6:1

So your 500kg weight could be putting a load of 50 tonnes or more into the top of your frame. But that number is just a (plausible) guess - don't use it to design anything!
 
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  • #7
AlephZero said:
I think you need some professional advice for designing this, since obviously a falling 500kg weight could cause a serious injury to the user.

As Baluncore implied, the force on the bolts will depend very much on how flexible the green (fabric?) slings are. Beyond that comment, IMO you need to do some proper calculations based on the full details of the structure, not just a photo and a couple of dimensions. Personally, I wouldn't like to guess if the bolts or something else would fail, and it would be a guess from the (lack of) information we have.

You could easily be talking about seriously high loads here. The multiplication factor from stopping the falling mass could easily be 10 or 20 times. Them you have a lever arm with a ratio that look like about 6:1

So your 500kg weight could be putting a load of 50 tonnes or more into the top of your frame. But that number is just a (plausible) guess - don't use it to design anything!


Thanks for the reply mate.

Sorry about the lack of information, I have no idea on engineering, which is why I'm posting here.

The green straps have 0 stretch in them.

I dropped 180kg from 1m into the straps, and guessed around 10cm of flex from the structure.


This is a reply I got from Facebook;

Okay, sorry man I've been at Ikea..

Basically, without knowing the angle of the member indicated by the yellow line, I've just had to do the calculations under the assumption that it acts perpendicular to the uprights.

The impact force of a 500kg object falling 1m = 49000 N

To find the moment force about the bolt you multiply that by 0.88m, which = 43120 Nm

Which is about 4397 Kg/m. So across 240mm that's giving me like... 18,320 Kg of force distributed between the two bolts.

This is by no means the full story though, to give you an accurate measurement I would need to determine the compressive force on the front bolt and the tensile force on the back bolt, as well as whether or not they're in single or double shear. Which would still only give you a static result, from there you could then start looking at what's happening to the bolts and welds and **** dynamically.

Patrick, that's not plastic deformation, that's the "recoil" of the falling object. And 0.1m movement in the bar after impact seemed pretty reasonable based on Scott's test video. Plus, the lower that value is (distance traveled after impact) the higher the impact force becomes. So if you take it down to say.. 5-10mm the impact force value becomes something like 490^12kN

^^Completely agreed with Patrick on that. The rating of 8.8 grade M16 bolts isn't worth jack **** if they're subjected to multi-planar force (heavy **** stressing it in several directions at once), which a half-ton impact will certainly do. So if someone fails while going heavy, it's worth replacing them.
 
  • #8
Stickyman: In your video, I saw your system deflecting about 60 mm, not 100 mm like you estimated in post 7. I currently estimated 60 mm, unless you have more accurate data. Therefore, using a 60 mm deflection, I currently obtained a system stiffness of k = 704 250 N/m.

Are you sure you want to design the pivot point bolts for a 500 kg mass, dropped from a height of 1000 mm? When I checked this, the dynamic amplification factor was 18.0, and the M16 property class 8.8 bolt, located at your pivot point (red arrow) shown in post 1, was stressed to 380 % of the allowable stress, which exceeds 100 %, and therefore would be grossly overstressed. (And this assumes one end of your bolt has threads in the shear plane.)

The above is quite different from your test video, which used only a 182 kg mass dropped from a height of 650 mm. Therefore, what is the maximum mass and drop height you want the bolt to withstand?
 
  • #9
nvn said:
Stickyman: In your video, I saw your system deflecting about 60 mm, not 100 mm like you estimated in post 7. I currently estimated 60 mm, unless you have more accurate data. Therefore, using a 60 mm deflection, I currently obtained a system stiffness of k = 704 250 N/m.

Are you sure you want to design the pivot point bolts for a 500 kg mass, dropped from a height of 1000 mm? When I checked this, the dynamic amplification factor was 18.0, and the M16 property class 8.8 bolt, located at your pivot point (red arrow) shown in post 1, was stressed to 380 % of the allowable stress, which exceeds 100 %, and therefore would be grossly overstressed. (And this assumes one end of your bolt has threads in the shear plane.)

The above is quite different from your test video, which used only a 182 kg mass dropped from a height of 650 mm. Therefore, what is the maximum mass and drop height you want the bolt to withstand?

Awesome, that's such a great reply, thank you.

In real life, the most weight that will be attempted will be 380-425kg.
The fall into the straps in normally much shorter than in the vid I posted, I'm just trying to make it as safe as possible.

I could move up bolt sizes if needed.
 
  • #10
Stickyman: So would the maximum drop height be about 800 mm? Do you want to use ISO property class 8.8 bolts? Or property class 10.9 bolts?

Can you post the dimensions (mm) of your lug and clevis plates, at the pivot point bolt (red arrow in post 1)? From a front view, it will look something like my attached file. Dimension t1 is the thickness of your lug, t2 is the thickness of your clevis plates (one clevis plate on each side of the lug), and gp is the gap between the lug and each clevis plate (when the lug is centered between the clevis plates).
 

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  • #11
I can use what ever bolts I need to, but currently 8.8.

The plates are all 10mm thick, and there is 8mm clearance gaps either side... A little to loose I know :(
 
  • #12
Stickyman: Your current gaps are terrible. I would not want those gaps to be more than about 0.5 mm, each. Is that something you could redesign?
 
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  • #13
I can close them up easy enough.

Will it make the structure that much weaker as is?

This whole thing has been made with a 5" grinder, drill press and a mig.

I don't have top gear.
 
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  • #14
Stickyman: For a 425 kg mass, dropped from a height of 800 mm, for the pivot point bolt, it currently appears you would need t1 = 24 mm, t2 = 12 mm, gp = 0.5 mm, and an M30 x 3.5, property class 8.8, bolt.
 
  • #15
Awesome.

Thank you very much.

If it's not a huge trouble, can you give me a brief run down on the calcs?
 
  • #16
Stickyman: That would be too lengthy and too detailed.

I want to point out though, the mass and drop height (and force) corresponding to post 14 is far more force than what you tested in your video. Even though the force in your video is much less, you can see, in the video, the structure looks like it is already being pushed to limits. I am doubtful your structure and weldments could withstand the far greater force corresponding to post 14. See what I mean?
 
  • #17
I do mate, I do indeed.

That's why I posted.

I'll redo the bolts as per your recommendation, and thicken t1 and t2, whilst moving the clearance to .5mm.

I'm also going to shorten lever arm ( yellow line) from 880mm to 600mm.

Thanks for your help mate, much appreciated.
 
  • #18
Stickyman: First let me mention, I think energy losses in this particular system are no more than 2 or 3 percent, and are therefore negligible.

Secondly, if you could measure the deflection for us, as follows, it would be appreciated. Place the empty steel barbell rod (with no disk-shaped masses installed yet) in the green slings, and measure the exact distance, in mm, from the floor to the bottom of each green sling.

Next, install any amount of disk-shaped masses onto the barbell rod, preferably a high mass, or fairly high mass (such as your 180 kg, or 350 kg). (And let us know exactly how much mass, in kg, you installed.) Now measure the exact distance from the floor to the bottom of each green sling.

If you could do this, and post this data, it would enable us to compute the system stiffness k1, and would be really interesting, and important.

Third, I think I now notice that your structure has a rear brace only on one side, where a hydraulic actuator is installed. This is quite different from what I thought yesterday, and it would cause the structure to be loaded very unevenly, causing a vast majority of the load to go to the side containing the rear brace. This makes it much more difficult (and inaccurate) to compute. If you are going to keep the structure designed asymmetrically like this, then we would need to rethink the answers, and it would become more complicated.
 
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  • #19
nvn said:
Stickyman: First let me mention, I think energy losses in this particular system are no more than 2 or 3 percent, and are therefore negligible.

Secondly, if you could measure the deflection for us, as follows, it would be appreciated. Place the empty steel barbell rod (with no disk-shaped masses installed yet) in the green slings, and measure the exact distance, in mm, from the floor to the bottom of each green sling.

Next, install any amount of disk-shaped masses onto the barbell rod, preferably a high mass, or fairly high mass (such as your 180 kg, or 350 kg). (And let us know exactly how much mass, in kg, you installed.) Now measure the exact distance from the floor to the bottom of each green sling.

If you could do this, and post this data, it would enable us to compute the system stiffness k1, and would be really interesting, and important.

Third, I think I now notice that your structure has a rear brace only on one side, where a hydraulic actuator is installed. This is quite different from what I thought yesterday, and it would cause the structure to be loaded very unevenly, causing a vast majority of the load to go to the side containing the rear brace. This makes it much more difficult (and inaccurate) to compute. If you are going to keep the structure designed asymmetrically like this, then we would need to rethink the answers, and it would become more complicated.

Hi nvn.
Yes, the pivot arm is only secured on the right side the bottle jack makes the top move up and down for height adjustments.

These are called monolifts, and are used in powerlifting competitions.

All the monolifts I've ever seen are built this way, which is why I half copied the design.
I do agree that the structure will be loaded very unevenly though.

I will be at the gym in 20 min, so can let you know the amount of deflection on the 880mm arm then.
I probably will reduce the lever arm to around 600mm though to help stiffen everything up. :)

Once again, I appreciate your help.
 
  • #20
With a 20kg barbell in the sling, it's 772mm off the floor.

With the barbell loaded to 410kg, it's 685mm
 
  • #21
Hi Stickyman,

I searched "monolift" to learn more about how they are used and found that indeed they have that actuator on only one side. It's strange from a design loading point of view. But I now understand why your video showed such an asymmetrical outcome - the whole mechanism rotated to the left and the weights shifted to the left (relative to the man standing at the beginning of the video) because the left side flexed more than the right side.

I agree with nvn that it complicates all the load calculations - those are for symmetrical loading. But you could also assume that ALL the load goes through one side i.e. twice the load. It will oversize the bolt, but what's the cost of a bigger/stronger bolt compared with the collapse of the structure and serious injury?

Having said that, a key factor in the calculation is the falling distance. I understand that they are safety slings and they have to be long enough for someone to do squats. I would strongly urge you to use the shortest slings possible - that would minimize the load on the bolts and hence the size of the bolts.

But I also realize from the videos that this is an add on feature to the basic monolift design - it was never really designed to take falling weights. How about adding a separate arm to support the slings? This could be rigidly welded, instead of working through a pivot and it opens up more ways to design the support structure that could be a far stronger and more rigid arrangement.
 
  • #22
Mate, that is a perfect idea!

I will build it tomrrow.

I was thinking something like this, out of 100x100.

ED55ABBA-C597-4D3B-ABA5-6ADE35698E77_zpsn7pqowub.png
Suggestions?
 
  • #23
Stickyman: There is an old adage, "Measure twice, cut once." Are you sure you measured those distances in post 20 accurately? Did you check them twice? They are the static (non-moving) floor-to-sling distance with the 20 kg empty barbell rod, and the floor-to-sling distance after adding 410 kg of mass to the barbell rod, right? And these measurements are when the barbell rod and masses are gently placed in the green slings, not dropped, and are not moving (static).

If your measurements in post 20 are very accurate, then that is vastly different from what I estimated in post 8, and very different from your estimate in the fourth line of post 7.

If post 20 is correct, then it means the deflection of the system in post 1, in your test video in post 2, assuming a drop height of 650 mm, was 264 mm. I am finding that hard to accept, yet.

What is the center-to-center height of the concrete blocks in the wall behind the monolift? Is it 200 mm? If you watch the video carefully, I thought it looks like the distance from when the green sling is fully extended but unloaded, to when the sling is fully loaded, is slightly more than one half of a concrete block, which would be roughly 120 mm, right? But keep in mind, the distance on the concrete blocks is magnified, due to perspective, because the wall is further away. Therefore, it implies a deflection of perhaps 100 mm (?). But according to post 20, it would be a deflection of 264 mm. :confused: This is quite a discrepancy, so far.

On another subject, would you be able to post dimensioned sketches of your structure, in mm? Because your structure is asymmetric, we need to be able to know all the dimensions. We also need all the member cross-sectional sizes, such as 100 x 100 x __ mm, where the blank is tube wall thickness.

I am not quite convinced yet regarding fixed sling supports. They will still be highly loaded, and possibly will interfere with usage (?), and will make the structure more complicated (?). Sometimes, simpler is better, if you make it strong enough.

I generally would say, change the design based on stress levels, instead of changing the design before you know a few of the stress levels. You can always change the design after you know a few of the stress levels. Therefore, the most important things first are, ensure the measurements in post 20 are accurate, confirm whether the dynamic deflection in the post 2 video is 264 mm or not, and post dimensioned sketches (side view, front view, etc.). You could also post dimensioned sketches of your proposed redesign.
 
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  • #24
Two points:
1. check the welds at the bottom where the upright meets the extension on the floor. That is another weak spot that could fail unexpectably. The thing was bouncing around in your test and a weld could have a crack in it.

2. Do the testing in a safer manner. With a failure, you will not be able to move out of the way fast enough to avoid injury. You might think so, but it will fail quicker than you can run.
 
  • #25
nvn said:
Stickyman: There is an old adage, "Measure twice, cut once." Are you sure you measured those distances in post 20 accurately? Did you check them twice? They are the static (non-moving) floor-to-sling distance with the 20 kg empty barbell rod, and the floor-to-sling distance after adding 410 kg of mass to the barbell rod, right? And these measurements are when the barbell rod and masses are gently placed in the green slings, not dropped, and are not moving (static).

If your measurements in post 20 are very accurate, then that is vastly different from what I estimated in post 8, and very different from your estimate in the fourth line of post 7.

If post 20 is correct, then it means the deflection of the system in post 1, in your test video in post 2, assuming a drop height of 650 mm, was 264 mm. I am finding that hard to accept, yet.

What is the center-to-center height of the concrete blocks in the wall behind the monolift? Is it 200 mm? If you watch the video carefully, I thought it looks like the distance from when the green sling is fully extended but unloaded, to when the sling is fully loaded, is slightly more than one half of a concrete block, which would be roughly 120 mm, right? But keep in mind, the distance on the concrete blocks is magnified, due to perspective, because the wall is further away. Therefore, it implies a deflection of perhaps 100 mm (?). But according to post 20, it would be a deflection of 264 mm. :confused: This is quite a discrepancy, so far.

On another subject, would you be able to post dimensioned sketches of your structure, in mm? Because your structure is asymmetric, we need to be able to know all the dimensions. We also need all the member cross-sectional sizes, such as 100 x 100 x __ mm, where the blank is tube wall thickness.

I am not quite convinced yet regarding fixed sling supports. They will still be highly loaded, and possibly will interfere with usage (?), and will make the structure more complicated (?). Sometimes, simpler is better, if you make it strong enough.

I generally would say, change the design based on stress levels, instead of changing the design before you know a few of the stress levels. You can always change the design after you know a few of the stress levels. Therefore, the most important things first are, ensure the measurements in post 20 are accurate, confirm whether the dynamic deflection in the post 2 video is 264 mm or not, and post dimensioned sketches (side view, front view, etc.). You could also post dimensioned sketches of your proposed redesign.

I'm 100% the dimensions in post 20 are correct.
I think the fact that it's only loaded in one side causes the frame to twist, there fore adding to the distance between 20kg barbell and 410kg barbell at static measurement.

Here is a very poor sketch, all materials are 100x100x3 RHS or 75x10 flat bar.

1EDE8892-7405-4A45-91FD-A9E8EE6F87BF_zpszfrauigm.jpg



Why are you not sold on the catching arms?
It would elevate all of the stress on the bolts, and load the frame symmetrically.
It also shouldn't interfere with the use of the monolift.

8322A73C-2784-4217-8DD0-7DE32CE5B2D1_zpsuijycl9v.jpg
 
  • #26
256bits said:
Two points:
1. check the welds at the bottom where the upright meets the extension on the floor. That is another weak spot that could fail unexpectably. The thing was bouncing around in your test and a weld could have a crack in it.

2. Do the testing in a safer manner. With a failure, you will not be able to move out of the way fast enough to avoid injury. You might think so, but it will fail quicker than you can run.

1. The tall uprights are bolted to a smaller ( 600mm) upright via 4 M16 8.8's.
I will check the welds for those though, and the welds that hold the tabs that the bolts go through.

2. I did have the bar set on top on beer kegs, but that ended up being more dangerous.
I did show that video to my mother, she almost had a heart attack.

A safer method will be found.
 
  • #27
Stickyman said:
2. I did have the bar set on top on beer kegs, but that ended up being more dangerous.
.

Beer kegs are probably not the best supports, but the way I would have tested it was something like.

1. Support the loaded bar in the slings.
2. Raise it to "balance" it on top of something like a trestle, close to the edge.
3. Lower the slings to give the free fall distance you want.
4. Push the bar off the trestle, from a safe distance, with a long pole!
 
  • #28
I suggested fixed supports because of your video. The barbell didn't fall evenly - the right side (as in previous post - your right when standing there) went down first and rebounded first - causing the whole barbell to rotate. The slings were not anchored, and so they slid towards each other and the barbell ended up with the left side on the ground. Along with the whole structure bouncing around, the potential for injury is high - to people standing around as well as the lifter. I echo 256bits here - no human can move fast enough.

Although I would usually agree with the philosophy espoused by nvn, in this case, I would consider the basic monolift design to be flawed for the purpose of catching a falling barbell. The bolt can be strong enough, but the asymmetries in design as well as actual usage (as in the video) cause things to move sideways - which is a hazard to the helpers who usually stand around. So fixing the bolt size is elegant for the purpose of a monolift, but does not fix the problem of bouncing dangerously. Fixed supports are an added complication, but fairly easy to do. I believe they don't interfere with powerlifting - but you are the better judge of that.

Your design of fixed supports should work - I haven't done any calculations but given that the existing structure survived the test, I expect the supports to take the load too. It will concentrate stress where the inclined member meets the upright, but I see from your drawing that there is a reinforcing plate (?) between them. That's a good idea to help spread the load and strengthen that point. To be safe, you should get an analysis done for the modifications.

The slings must be firmly anchored to the supports - they won't slide around anymore, but they could bounce off the arms. This way, it is less likely to end up with one end of the barbell on the ground.

But do remember that there will still be a lot of bouncing around. All the energy from the falling barbells has to go somewhere, and the bouncing helps to dissipate energy. But with a symmetrical design, it is less likely to bounce sideways. Making the system more rigid changes the way it bounces - it still needs to dissipate energy somehow and will still bounce - I expect the slings will have to do more of the bouncing. Adding mass does reduce the amount of bouncing. If you filled the 100X100 with sand it would help to weigh it down and add damping to the system.

Ideally, you need a damper system - if you had shock absorbers in line with the slings, the energy would be dissipated safely. I'm no expert on shock absorbers, and this would start getting complicated again - but it should work. Something for you to consider, and which your mother will appreciate!
 
  • #29
Stickyman said:
Why are you not sold on the catching arms? It would elevate all of the stress on the bolts, and load the frame symmetrically. It also shouldn't interfere with the use of the monolift.
Stickyman: I was feeling a slight bit of trepidation when I first read about the proposed change, because I was not visualizing the change clearly yet, at that moment; and I speculated that it might interfere. Now that you posted sketches, it becomes more clear.

One thing I notice in your design in post 25 is, the left and right sides of the structure are not connected, except at a wobbly clevis connection, at the top. This will make the structure more wobbly, shaky, and weak.

The structure will also be somewhat weak in the forward and aft direction, because there is no diagonal brace at the bottom of the upright tube. You have only the 600 mm vertical tube behind the upright tube, but that is not nearly as strong as a diagonal brace.

Now that you confirmed your measurements in post 20, it means the stiffness of the system in post 1 is k1 = 46 230 N/m. This would mean the total deflection in your test video in post 2, if we assume a 650 mm drop height, is supposedly 264 mm; and the amplification factor is 6.92. (I did not think the deflection was this much, when I looked at the video.)

Therefore, if we assume a 425 kg mass, and an 800 mm drop height, then it means the system in post 1 would have an amplification factor of 5.33, and would deflect 481 mm, unless it collapses first. (Multiply the static weight by the amplification factor to obtain the dynamic applied force.)

Back to post 25, your design in post 25 will have the same static moment on the base of the upright members as your post 1 design. In other words, there is no reduction in your moment arm. The catching arms are still 875 mm. But there is no significant brace at the lower end of the upright, as I mentioned in paragraph 3, and as 256bits touched on. However, if there were a diagonal brace there, it would be skew, which reduces its efficiency.

What is the material specification number for your square tubes? And what is the material specification number for your 75 x 10 mm flat bar? What is the material name/number of your weld material?

Could you add the following dimensions to your second sketch? Add the width across the outer base tubes; the dimension to the end of the angled tube in the base (and the dimension to the beginning of the angled tube, if not flush with the upright tube); the horizontal dimension at the bottom of the 885 mm bar; the horizontal dimension to the 45 deg diagonal brace in the catching arm.

Later, could you add a dimensioned close-up side view sketch of the 885 mm bar, including how the hydraulic actuator is attached, and dimensions to the hydraulic actuator attach points?
 
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  • #30
Stickyman: Here is another measurement we really need, on your post 1 structure. Very accurately measure from the floor to the bottom face of the square tube where each sling is attached, first with the 20 kg empty barbell rod installed in the green slings. Next, add 410 kg of mass to the barbell rod, then measure again from the floor to the bottom face of the square tube at each sling. Please post these results.

Or, if it is hard to accurately measure to the bottom face of the square tube, you can instead put a pencil mark on the side of the square tube where each sling is attached. Then measure from the floor to each pencil mark, first with the 20 kg empty barbell rod installed, and secondly after adding 410 kg.
 
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  • #31
Wow, awesome replies guys, sorry I have missed them until now.

I ended up making that brace but added a section above to connect them and hang the slings.

These are welded straight to the frame as I did not have any flat bar suitable and the steel stores are closed for xmas.

I got caught up in the moment, and forgot to take all the measurements of this test, but I think it performed much better.

Here is a video of 220kg.

 
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  • #32
On second view, the barbell falls just over 1 plate width.

The free fall would have been just over 450mm.
 
  • #33
Stickyman: Which plate were you referring to, in post 32, when you said "1 plate width"?

The mass is falling and hitting almost a hard stop. The stiffer you make the system, the more the impact force skyrockets. I agree with the post by munster; a damper or shock absorber would be good. How about if you attach, say, ten pieces of velcro to the sling, then make ten small folds in the sling, attaching the velcro, like an accordion? Then when the mass falls, the velcro must disconnect along the way, thereby reducing the barbell descent velocity.

I agree with the post by 256bits; one of the highest stresses currently occurs in the horizontal square tube "foot," just before it connects to the lower end of the upright square tube. The static normal stress on this cross section is, sigma1 = 0.5(825 mm)(425 kg)(9.81 m/s^2)(50 mm)/(1 827 092 mm^4) = 47.06 MPa. But sigma1 must still be multiplied by a dynamic amplification factor, which we do not know yet, but which could be, say, 5 to 20. Any of these values overstress that cross section. (And that cross section is also subjected to some torsional shear stress, but we do not have all the structure dimensions yet.) Therefore, the diagonal brace I mentioned in post 29 would be helpful. But also, the damper, mentioned above, is critical. Otherwise, I currently doubt you could go up to a 425 kg mass without exceeding the structure allowable stress.
 
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  • #34
Thanks for the reply NVN.

The plate I am referring to is a "weight plate", sorry, gym talk.
A weight plate/disc is 450mm in diameter.

I realize that the stiffer you make the frame, the higher the stresses become, that's why I was happy with the level of "bouncing" it did.
Not so much that it was going to flip, but enough to "help" dissipate the energy from the falling barbell.

The velcro idea sounds plausable, but I really like the idea of adding a car/motorcyle shock absorber to the frame, but that will take some thinking.

The uprights are joined by a (loose) clevis joint, 50x50x3mm RHS (just below the clevis), and a 100x100x3mm post that the slings now hang from.

As far as the bracing the footprint goes, there are not a lot of options on this style of monolift, at least on this particular one.

In future, I could modify it to allow bracing at the bottom.

What you need to work out a SFL on the current design? Also, out of curiosity, what do you do for work NVN, you seem very intelligent, at least to a carpenter like me haha.
 
  • #35
What about something like this?

http://safetysling.thomasnet.com/item/gripper-mesh-slings/g-35-heavy-duty/4005
 
<h2>1. How is the load on bolts calculated?</h2><p>The load on bolts is calculated by multiplying the force applied to the bolt by the distance from the center of the bolt to the point where the force is being applied. This is known as the moment arm and is measured in units of length.</p><h2>2. What factors affect the load on bolts?</h2><p>The load on bolts can be affected by several factors, including the type and size of the bolt, the material it is made of, the amount of torque applied during installation, and the external forces acting upon the bolt.</p><h2>3. How do you determine the maximum load a bolt can withstand?</h2><p>The maximum load a bolt can withstand is determined by its tensile strength, which is a measure of how much force it can withstand before breaking. This value can be found in engineering tables or by conducting a tensile strength test on the specific type of bolt being used.</p><h2>4. What happens if the load on bolts exceeds their maximum capacity?</h2><p>If the load on bolts exceeds their maximum capacity, they may fail and break, causing the structure or equipment they are supporting to collapse. This can lead to serious safety hazards and should be avoided by ensuring that the bolts are properly sized and installed.</p><h2>5. Can the load on bolts change over time?</h2><p>Yes, the load on bolts can change over time due to factors such as corrosion, wear and tear, and changes in the external forces acting upon the bolt. Regular inspections and maintenance can help to identify any changes in the load on bolts and prevent potential failures.</p>

1. How is the load on bolts calculated?

The load on bolts is calculated by multiplying the force applied to the bolt by the distance from the center of the bolt to the point where the force is being applied. This is known as the moment arm and is measured in units of length.

2. What factors affect the load on bolts?

The load on bolts can be affected by several factors, including the type and size of the bolt, the material it is made of, the amount of torque applied during installation, and the external forces acting upon the bolt.

3. How do you determine the maximum load a bolt can withstand?

The maximum load a bolt can withstand is determined by its tensile strength, which is a measure of how much force it can withstand before breaking. This value can be found in engineering tables or by conducting a tensile strength test on the specific type of bolt being used.

4. What happens if the load on bolts exceeds their maximum capacity?

If the load on bolts exceeds their maximum capacity, they may fail and break, causing the structure or equipment they are supporting to collapse. This can lead to serious safety hazards and should be avoided by ensuring that the bolts are properly sized and installed.

5. Can the load on bolts change over time?

Yes, the load on bolts can change over time due to factors such as corrosion, wear and tear, and changes in the external forces acting upon the bolt. Regular inspections and maintenance can help to identify any changes in the load on bolts and prevent potential failures.

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