Board logo

Is my bracket strong enough? Real engineers please help
johnH20 - 16/5/17 at 08:30 PM

An important question as it is an extension bracket to mount the shoulder straps of my harness. The bracket is held a horizontal plane by two 7/16 'S' grade seat belt bolts in single shear. The harness brackets themselves are similarly mounted outboard on each side by 40 mm. I know the load in the seat belts ( FIA mandated ) and can calculated the shear load on the bolts. The question is the local failure load on the holes in my extension bracket i.e. the pull out load. I have a qualitative understanding of the stress distribution around the hole but do not know how to calculate the failure load. Many attempts on Google have failed to find an engineering text on the theory of bolted joints that will solve this problem. I must be asking the wrong question. Real Engineers please help

craigdiver - 16/5/17 at 09:12 PM

quote:
Originally posted by johnH20
An important question as it is an extension bracket to mount the shoulder straps of my harness. The bracket is held a horizontal plane by two 7/16 'S' grade seat belt bolts in single shear. The harness brackets themselves are similarly mounted outboard on each side by 40 mm. I know the load in the seat belts ( FIA mandated ) and can calculated the shear load on the bolts. The question is the local failure load on the holes in my extension bracket i.e. the pull out load. I have a qualitative understanding of the stress distribution around the hole but do not know how to calculate the failure load. Many attempts on Google have failed to find an engineering text on the theory of bolted joints that will solve this problem. I must be asking the wrong question. Real Engineers please help


In a production process, these complex stresses would be modelled at a design stage using computer software. In the real world, lifting (load bearing) equipment is tested to a safety factor by loading up the load bearing member to a factor greater than the anticipated maximum load. In my opinion, make another similiar one and subject it to a load considerably greater than you would expect (your upper body mass plus the g-force induced additional mass of a potential impact (would think this data would be available on google). OR have simeone model it, and do a stress analysis on solidworks.

ian locostzx9rc2 - 17/5/17 at 05:35 AM

I think you should put a photo up that may help with replies.

russbost - 17/5/17 at 07:52 AM

John, can you clarify, is it the "pull through" load you are trying to work out, ie (if I'm understanding the construction correctly) if you were to pick the car up vertically by the seat belts at what point do they pull through the bracket? (or presumably detach the bracket from whatever it's attached to)

You've not said what the brackets are attached to, nor what thickness steel they are. As the car was recently IVA'd, the inspector concerned would have raised any points he felt were debatable.

As said, I think a photo & a bit more info would help

johnH20 - 17/5/17 at 02:03 PM

Well further research and I think I have found what I need. A couple of sources for engineering calculations that might be of use to others that I found are www.roymech.co.uk and www.Engineersedge.com. Having reviewed my bracket I think I am going to make it stronger for increase factor of safety!