Lifting gantry

[fizzy]

I have a nice gantry rated at 3 tons but it is too narrow. Only 8 feet wide. Just too narrow for a flatbed lorry
Easiest fix I suppose is to replace the top beam.
Why are the ends shaped like this and not just a straight RSJ? Does it add strength?

 

[Parm]

Be interested to see what the answer may be?

Never see one like that

 

[Beeezer]

My thinking.. as it’s so narrow it was a tight fit in someone’s workshop and the ends are like that to miss roof trusses…..

 

[fizzy]

Looks professionally done though. It's not a home made jobbie. Got a proper rating plate on it etc. Will have to take another picture tomorrow when it's daylight.

 

[fizzy]

Redirect Notice

This one has tapered ends as well

 

[James1979]

If you follow your link there’s actually a few.
My guess would be stiffness. Ie to stop it twisting along its length.

just thinking about if you lift something that’s not exactly under the beam you’ll impart a twist into it? Dunno really but interested to find out.

 

[Brad93]

In theory you've kind of made a J stiffener there by angling the end but not really done a great deal because you've removed the top flange.

I think it's been done purely for aesthetic or clearance reasons.

 

[frank horton]

brads correct...I've don it a couple of times.....much neater than abrupt end....

 

[Agroshield]

Other than the far more likely aesthetic or space-fitting reasons above, there is a possible (but unlikely) structural explanation.

There is a failure mechanism in I-beams called web buckling. It occurs when the web (vertical part of the I) is in compression. From memory, the buckling resistance goes down with the square of the depth. So something like the gantry, with roughly half-height webs at the ends would have four times the buckling resistance at that point.

If you stand looking along the beam and pull one of the legs towards you to move the gantry, your pulling force, combined with the long lever arm of the leg leads to rotation at the top that puts the web into compression.

An alternative to your design is to plate the ends, but that takes extra material. With yours, you can slice off the top flange, cut a wedge out of the web and weld the flange back on.

 

[8ob]

All the gantries I have had have been the same as the one above, never really gave it much thought other than it stops the chain block trolley flying out of the end when its dismantled.

Bob