Bridge Crane designs and ideas...38' span

[LD1]

I meant to ask about the flanges. (thats where the strength is). ASsuming its 6" x ~1/4" also, that makes it a W6x15# beam.

For my calculations I was using A36 steel with 36ksi yield strength. So a 5:1 safety would limit allowable to 7200psi. Most beams are actually a992 which is 50ksi so a 5:1 would allow 10ksi stress.

Assuming the beam above, a 1000# load would be 8660psi stress and 0.905" deflection. NO that would not scare me.

1500# is 13ksi stess and 1.36" deflection. While exceeding a SF of 5:1, still a good ways from failure.

 

[Mace Canute]

LD1, a friend has half a dozen 20 foot lengths of what I believe is W31 beams (8" x 8", web and flange thickness seems to be very close to dimensions given for W31). I have no idea what grade of steel they are made from though so I guess you would have to assume it's the lowest grade available. He wants to use them to build a gantry crane and use one of the beams full length for the top beam. Could you please do the calculations for me to see what the maximum safe load would be with both a 5:1 and 2:1 safety factor?

 

[LD1]

Assuming A36 steel

5:1 max load 3300# and would deflect 0.288"
2:1 max load 8250# and would deflect 0.720"

Static Load Failure would occur at 1.44" of deflection and 16,500# hanging on it.

If it were mine, id personally feel comfortable hoisting ~5k on it. Dynamic conditions hoisting and bouncing something are alot different than a static load. Thus why most are 5:1 for safety.

 

[LD1]

Assuming A36 steel

5:1 max load 3300# and would deflect 0.288"
2:1 max load 8250# and would deflect 0.720"

Static Load Failure would occur at 1.44" of deflection and 16,500# hanging on it.

If it were mine, id personally feel comfortable hoisting ~5k on it. Dynamic conditions hoisting and bouncing something are alot different than a static load. Thus why most are 5:1 for safety.

 

[MichiganIron]

Wait...has anybody checked any of these solutions for Euler Buckling ??? The unbraced length of the top flange is critical in determining the allowable stress in a member induced to bending. Many beam tables only calculate the allowable load based on a braced top flange. Make sure the beam design accounts for the allowable stress reduction due to the total unbraced length of the top flange, including Euler Buckling. I can guess from experience (Registered Structural Engineer for 35 years) that a 6" flange will have a very low allowable bending stress at spans over 12'.

 

[Mace Canute]

Assuming A36 steel

5:1 max load 3300# and would deflect 0.288"
2:1 max load 8250# and would deflect 0.720"

Static Load Failure would occur at 1.44" of deflection and 16,500# hanging on it.

If it were mine, id personally feel comfortable hoisting ~5k on it. Dynamic conditions hoisting and bouncing something are alot different than a static load. Thus why most are 5:1 for safety.

Thank you! That is a lot more than I thought it would be. He'll be happy!

I'll wait to hear what people have to say about Euler Buckling before I pass any information on.

 

[mikefromnh]

Wait...has anybody checked any of these solutions for Euler Buckling ??? The unbraced length of the top flange is critical in determining the allowable stress in a member induced to bending. Many beam tables only calculate the allowable load based on a braced top flange. Make sure the beam design accounts for the allowable stress reduction due to the total unbraced length of the top flange, including Euler Buckling. I can guess from experience (Registered Structural Engineer for 35 years) that a 6" flange will have a very low allowable bending stress at spans over 12'.

NO you mean that a bunch of forum math shouldn't be relied upon for designing gantry cranes?

 

[LD1]

Thank you! That is a lot more than I thought it would be. He'll be happy!

I'll wait to hear what people have to say about Euler Buckling before I pass any information on.

With a wide flange 8x8 beam, no worries.

 

[Mace Canute]

With a wide flange 8x8 beam, no worries.

Thats going to make my friend's day! Thanks again!

 

[Streetcar]

With a wide flange 8x8 beam, no worries.

Ld
A structural engineer has said that unbraced length will control beam capacity. Why do you think the unbraced length is not important?
I assume you are designing using a beam table . The beam tables I have used are for braced flanges only