Pin-pin-free cantilever unbraced length
Pin-pin-free cantilever unbraced length
(OP)
I am designing a beam to be suspended from two parallel girders. The beam will be attached to the bottom flange of the girders and the free end will cantilever out to support two beams. The suspended beam will be attached to the girders by the top flange. The beams supported by the cantilever will be pinned connections resting on the top flange.
Girder Girder
_____ _____
| |
Load Load | |
| | | |
| | __|__ __|___
__\|/_______\|/_________\/_________\/__
I am having trouble deciding the correct unbraced length to use for designing the cantilever beam. If it were possible, the bottom flange of the cantlevered beam would not be supported along its entire length. Worst case scenario, the unbraced length would be the distance from left load to the right support. Can the unbraced length be considered from the left load to the left support? Any input would be appreciated.
Girder Girder
_____ _____
| |
Load Load | |
| | | |
| | __|__ __|___
__\|/_______\|/_________\/_________\/__
I am having trouble deciding the correct unbraced length to use for designing the cantilever beam. If it were possible, the bottom flange of the cantlevered beam would not be supported along its entire length. Worst case scenario, the unbraced length would be the distance from left load to the right support. Can the unbraced length be considered from the left load to the left support? Any input would be appreciated.






RE: Pin-pin-free cantilever unbraced length
If the bottom flange must be free and clear, say for a monorail hoist or something, then I would say that your full length is the unbraced length to use.
RE: Pin-pin-free cantilever unbraced length
RE: Pin-pin-free cantilever unbraced length
When I design cantilever beams, I assume the unbraced length is equal to the length of the cantilever even if the top flange is braced by a slab or roof deck.
as far as using the stiffeners for lateral bracing, AISC FAQ's has some discussion about lateral bracing and the use of stiffeners to prevent section rotation. here's the link, if it works:
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RE: Pin-pin-free cantilever unbraced length