Allowable Loads Suspended From Beam Flanges 3

[MattP]

Does anyone have any info on how to calculate allowable loads hanging from the lower flange of S shape and W shape beams? i.e. underhung crane trolley

Thanks,
Matt

 

[ishvaaag]

A first approximation you may get by the consideration in flexure of the cantilevered flange for an unfavourably eccentrical situation of one wheel. For concentrated loads 18 times the thickness -in this case of the flange- is sometimes considered a width giving safe enough dimensioning.

Once so dimensioned, a more proper check would be the identification of some (maybe dihedral, 2 symmetrical triangles) lines of roture mechanism that gives the plastic solution to the local rupture consistent with the position of the load, and then see if you have enough safety factor.

 

[austim]

Hi, MattP.

If you have any way of getting hold of a copy of the Australian Crane Code AS 1418, you will find the design of monorail beams well covered there. (I would be a little surprised if other crane codes didn't cover the problem just as well).

As well as considering transverse bending in the bottom flange (as ishvaag has indicated), you need to consider the local longitudinal stresses (which must be combined with the main beam bending stresses).

From memory, I think that the Aus Code lets you go very close to full yield stress when combining tensile stresses due to local and global bending (ASD design). Since there is matching local compression on the top surface of the flange, yield at the bottom face is very much a local effect, with no adverse consequence on the global strength of the beam.

You also need to consider the effect of out-of vertical loads, which can produce excessive bending stresses in the web. These may be reduced somewhat by proper design of the supports to the top flange. If they permit some degree of torsional rotation, then the web may deflect to reduce out-
of-plane loading.

 

[ishvaaag]

Certainly I didn't named longitudinal stress and should. Thanks, Austim.

 

[Dennis59]

Does anyone have ordering information for the Australian Crane Code AS 1418?

 

[eureka]

Crane Manufacturers Association of America (CMAA) Specification #74 also addresses the issue of hanging flange loads. Copies are available from the Material Handling Institute. Go to the web site,

http://www.mhia.org

 

[RockEngineer]

If you have access to old copies of the magazine "Modern Steel Construction" put out by AISC the Dec 1999 issue has a good article on calculating lower flange loading for underhung cranes on page 9 in the steel interchange section. The answer was by David T. Ricker who was a premier crane structural engineer for many years. His method gives slightly different answers than the CMAA 74 but you have an idea how you came up with your answer. CMAA 74 just gives you an equation and no background. If you don't have access to the article I can probably fax it to you depending on where you are in the world.