Determining adequate bolt size

[aec062859]

Hello,

I have a hoist equipped with a motorized trolley that needs end stops.

Each end stop will be made of Two 4"x4"x"6" L-shapes (one per side)and these two will be fastened to the monorail's web with TWO gr5 bolts.

Weight of trolley and hoist is 200 lbs, trolley speed is 30fpm. No elastometers will be used.

How do I determine the size of bolts to install?

Thanks!

Antonio

 

[JedClampett]

These are traditionally attached based on minimal analysis. I would say two 3/4 inch A307 bolts are fine. It's not intended to stop a big load.
Think of it this way: If someone runs the trolley full speed into the end stops and shears off the bolts, who are they going to be mad at, the guy abusing the trolley or the guy who designed the end stop?

 

[aec062859]

Hi Jed,

Thanks for your reply. I agree, however, I would like to see how kinetic energy is used to determine the shear force the bolts need to resist.

Would you have any idea?

Thanks!

aec062859

https://www.eng-tips.com/viewthread.cfm?qid=439291

 

[JedClampett]

Designing for impact is very difficult. Even for very low speeds, the forces can be shown to be enormous. You need the stiffness of not only your support, but the impacting body. Most of the time, there's a bumper or other shock absorbing device that needs to be taken into account. Your best bet is to assume some distance that it takes to stop the trolley (1/2"? 1/4"?) and use the physics of de-acceleration to calculate the acceleration value. Multiply that times your mass, and you have a force.

 

[Agent666]

If you had to justify it with some numbers I'd work out the load to yield the angles based on where they make contact and just make sure the bolt strength is higher than that. I think you will find the angles are going to yield well before you get anywhere close to developing the shear capacity of the bolts. Under a short term impact load they just continue to bend (until sufficient energy is absorbed), but the force on the bolts remains the same unless part of the hoist can impact with the leg attached to the web (so possibility of higher impact forces transferring directly to the web bolts).

Usually the stops on manual or powered hoist monorails are there primarily to ensure the hoist cannot fall off the end of the beam rather than as a dedicated buffer to be relied on to stop high speed impacts like you might see on a dedicated runway crane. The small powered (and manual) hoists I've had experience with generally move relatively slow, such that I'd suspect that they would just grind to a halt against the stops even under power. Not sure but hoists may well have some sort of protection to cut the power if they impact or get near to the stops?