How are bolts selected?

[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? How is kinetic energy used to determine the shear force the bolts must resist?

Thanks!

Antonio

 

[drawoh]

aec062859,

If your trolley decelerates instantly to a stop, you need infinitely strong bolts, and you need the rest of your structure to be infinitely strong. Where is your elasticity coming from? If you don't have a rubber spring element, you need some other spring element.

Do you understand impact analysis?

--
JHG

 

[aec062859]

drawoh,

I agree. without an elastic component, impact takes place. Unfortunately the force is not easily determined since it is a function of time of impact.

I am hoping someone knows how to determine the shear force using the kinetic energy of the trolley + hoist.

At the end, I will equip the end stops with an elastomer. I just want to be able to select the bolts assuming elastomers will not be used.

Thanks,

Antonio

 

[drawoh]

aec062859,

Your kinetic energy must be converted to strain energy. Read up on strain energy.

--
JHG

 

[Tmoose]

Depending on the (missing) orientation of the angle, the (missing) thickness of the angle flanges, the (missing) location of the bolts attaching the angle to the rail, the (missing) detail of how the trolley contacts the angle, and probably some other details as well, the trolley propelled by a thoughtless or vindictive human operator could have little difficulty in failing the bolts in short order.

F= ma
d=at²/2

https://www.calculatorsoup.com/calculators/physics/displacement_v_a_t.php

With my assumption about your assumption of no elasticity the distance used to slow the trolley = 0 , with attendant infinite acceleration, and exiting resultant infinite force.
Hence others comments about strain energy etc.

 

[hydtools]

You might try work = energy.
F, force to shear the bolt
d, the distance through which that force acts
m, mass of the trolley
v, the velocity of the trolley
F*d=(1/2)m*v^2

Ted

 

[Compositepro]

If you wanted to design a machine to shear the heads off of bolts, it would work just like your design.

 

[Jamesg83]

This isn't too tricky. Have a look at this link.. Lecture notes

Scroll down to the relevant section, which will depend on the orientation of your angles. There are expressions for beams in bending, cantilevers or tension/compression members. Assuming you know basic integration, you can equate the kinetic energy (m*v^2/2) to the strain energy as it has to balance. You can rearrange for the load and there you have it. If you're struggling I have these equations already integrated and rearranged from a pretty decent weldment design textbook by Omar Blodgett but it's not currently to hand.

You can then use this online [link Www.digitool.org]calculator[/url] to size the bolts for a given force or moment.

You need to make sure that you satisfy the goodman relation with a fatigue factor of at least 3 (common practice) as you'll be designing for infinite life. This calculator takes into account the Marin factors and stress concentrations at the root under the bolt head and root of the thread when calculating the endurance limit.

Disclaimer: Do lots of testing and ensure the stops fail safe.

 

[chicopee]

You have not said if the angles are uneven legs ie 4x6 whereby the 6" legs are the contact side with the trolley wheels. If so, you can then analyze the 6" side as a cantilever beam which under a point load from the wheels not exceeding the elastic limit of the steel. Point load at tip of 6"leg can then be calculated. That point load, depending how the bracket is bolted to the rails, will be either under tension from prying or under shear and prying if the bolting is under the rails. I am assuming that the angle thickness is already available otherwise Hydetools equation will need to be incorporated and work with the two concepts.