Question about A36 steel strength

[IndMechJeff]

If I have 1/4"T x 12"W x 60"L a36 steel how much weight will it hold in the center before it deforms?

 

[berkeman]

Welcome to the PF.

If I have 1/4"T x 12"W x 60"L a36 steel how much weight will it hold in the center before it deforms?

Approximately 1 microNewton...

Oh, deflects by how much? To the elastic limit?

 

[IndMechJeff]

Welcome to the PF.

Approximately 1 microNewton...

Oh, deflects by how much? To the elastic limit?

Yes. To the point where it's basically bent out of shape but doesn't return to its original shape with no load. I'm pretty new to all this so please excuse my ignorance while I try to figure it out. This 1/4" thick, 12" wide by 5 foot long steel would be supported on the long ends. Sort of like a trench.
It's basically intended to be a ramp for an aggressive curb so the load would roll from bottom to top.

 

[JBA]

For me your drawing with the right end on or attached to a curb and the left end sticking out horizontal with no support shown does not relate very well to your description of the application. Does the left end rest on the ground and the right end on a curb, in which case, the load might not be perpendicular to the top surface of the plate.

 

[IndMechJeff]

For me your drawing with the right end on or attached to a curb and the left end sticking out horizontal with no support shown does not relate very well to your description of the application. Does the left end rest on the ground and the right end on a curb, in which case, the load might not be perpendicular to the top surface of the plate.

Sorry for the crude drawing . The left end rests on the road, the right on the curb. The plate is supported evenly on the ground and the curb with the void underneath.

 

[ChemAir]

In a flat configuration, the answer to the question "What can it support without bending?" is "not much". A 1/4"x12" A-36 flat bar will sag visibly (>1/16") under its own weight at a 5' span with the ends unsecured, and you can flex it pretty easily (1/4" or so) with one hand. A person jumping in the middle could permanently deform the piece. Something heavier rolled into the ramp could also easily deform it over time in small increments, if not all at once.

If this description sounds too weak/flexible, and you need to make it more rigid, you can increase the vertical component or decrease the span. If you want to use 1/4" plate, I'd suggest forming it into a 12" channel with 1.5" or 2" legs. You'd need to modify this (miter) so it would sit flat on the ground and won't slip off the curb. If you can't accommodate the channel legs, you may be able to have an intermediate support to cut the span in half.

1/4" plate weighs about 10.2 lb/ft2, so these will be heavy, and with no handles, difficult to move. You might look at some trailer loading ramp designs to get some ideas to make it lighter weight if it needs real strength.

I'd encourage the inclusion of something to prevent the ramp from sliding when you use it. Using a loose ramp to move something that has driven or braked wheels is a recipe for relocating a ramp rather suddenly. A drive wheel can send the ramp away from the wheel, using the brakes on the ramp can drag it with the tire. You can find lots of Youtube truck ramp loading fails showing what not to do here.

 

[IndMechJeff]

In a flat configuration, the answer to the question "What can it support without bending?" is "not much". A 1/4"x12" A-36 flat bar will sag visibly (>1/16") under its own weight at a 5' span with the ends unsecured, and you can flex it pretty easily (1/4" or so) with one hand. A person jumping in the middle could permanently deform the piece. Something heavier rolled into the ramp could also easily deform it over time in small increments, if not all at once.

If this description sounds too weak/flexible, and you need to make it more rigid, you can increase the vertical component or decrease the span. If you want to use 1/4" plate, I'd suggest forming it into a 12" channel with 1.5" or 2" legs. You'd need to modify this (miter) so it would sit flat on the ground and won't slip off the curb. If you can't accommodate the channel legs, you may be able to have an intermediate support to cut the span in half.

1/4" plate weighs about 10.2 lb/ft2, so these will be heavy, and with no handles, difficult to move. You might look at some trailer loading ramp designs to get some ideas to make it lighter weight if it needs real strength.

I'd encourage the inclusion of something to prevent the ramp from sliding when you use it. Using a loose ramp to move something that has driven or braked wheels is a recipe for relocating a ramp rather suddenly. A drive wheel can send the ramp away from the wheel, using the brakes on the ramp can drag it with the tire. You can find lots of Youtube truck ramp loading fails showing what not to do here.

Thanks for the reply! I realize that my question needs further explanation. If you picture a driveway curb, this piece would be 5 feet long (left to right) and 12" to span from the street to the top of the curb. So it's supported on the long edges.

 

[JBA]

Please excuse my directness, but what your question needed was an accurate description of the application.
Just as an exercise I ran an analysis of your application (fortunately I used an Excel worksheet so all I had to do after your correction was switch the length and width input values) and, while you haven't stated your anticipated load, I calculated the loading that would result in a stress equal to 1/2 of the plate's min.yield strength of 36,000 psi (a Safety Factor of 2) and using that limit, and the analysis indicates that the maximum allowable center load would be 3700 lbs. with a plate center deflection of 1/16". All of the equations for the analysis are from the "Machinery Handbook" 22nd Edition.

At the same time all of the issues on plate slipping stated by ChemAir still apply and if you had the opportunity to observe someone loading a car on a trailer using two long boards as the ramps you would understand his concerns. The steeper the angle of the ramp the more likely it will try to slide forward due to the horizontal force of the wheel pushing on it so it would be a good idea to weld a strip across the plate that will push on the curb to help prevent that from occurring.

 

[IndMechJeff]

Please excuse my directness, but what your question needed was an accurate description of the application.
Just as an exercise I ran an analysis of your application (fortunately I used an Excel worksheet so all I had to do after your correction was switch the length and width input values) and, while you haven't stated your anticipated load, I calculated the loading that would result in a stress equal to 1/2 of the plate's min.yield strength of 36,000 psi (a Safety Factor of 2) and using that limit, and the analysis indicates that the maximum allowable center load would be 3700 lbs. with a plate center deflection of 1/16".

At the same time all of the issues on plate slipping stated by ChemAir still apply and if you had the opportunity to observe someone loading a car on a trailer using two long boards as the ramps you would understand his concerns. The steeper the angle of the ramp the more likely it will try to slide forward due to the horizontal force of the wheel pushing on it so it would be a good idea to weld a strip across the plate that will push on the curb to help prevent that from occurring.

Thank you for the time you've spent on this! I plan to affix a strip along the bottom edge to prevent the plate from kicking out. I was just concerned about the weight limitations of the thin plate (which would determine what could be driven across it) again, thank you all for your time spent. It's greatly appreciated!