Hoist beam local flange bending

[tebodm]

I am working on analyzing an existing steel hoist beam (W14x74) that is being re-purposed for a different hoisting configuration. The client is looking to install a pair of adjustable locking-jaw clamps (see attached file, BC-1 clamps) onto the bottom flange of the beam for hoisting 45,000 pounds. The configuration would be similar to a bottom-flange monorail. I have reviewed this forum and am stuck at how to treat the length (and area) of the bottom flange that would contribute to the bending resistance. I have reviewed CMAA and the Dec '99 Modern Steel Construction Interchange (attached). Both of those references assume a concentrated point load from the wheel of the crane/hoist. The clamp that is proposed has a jaw length of approximately 8" so it seems like I should be able to at least distribute this loading along the length of the clamp jaw and use an 8" + 2e length (area) in the calculations outlined in the Steel Construction article.

http://files.engineering.com/getfil...8eb4-1eee4935874b&file=Renfroe_Beam_Clamp.pdf

http://files.engineering.com/getfil...dern_Steel_Dec_1999_bottom_flange_bending.pdf

 

[NOLAENG]

The fact that AISC won't touch this topic with a 10 ft pole annoys me. I have no idea why they won't put a design guide out for bottom flange local bending considering how many times people ask them about it. The catalog pdf lists working load limits. I would be hesitant to use that clamp for a load larger than their listed working load limit. What is their safety/design factor for those clamps? Also, I'm not sure about the 8" + 2e for the distributed length. If you use 8" for the length, is the beam is overstressed? I recommend this article as another reference

http://www.aisc.org/store/p-2288-flange-bending-in-single-curvature.aspx

. Even if you aren't an AISC member it is definitely worth the $10. Sorry if my response isn't the best but I'm a younger engineer who has struggled with similar situations.

 

[Hokie93]

This issue is addressed in the paper "The Performance and Design Checking of Chord-Angle Legs in Joist Girders" by Ted Galambos (AISC Engineering Journal, Third Quarter, 2001). The result presented in the paper is P[sub]p[/sub] = (M[sub]p[/sub]/e*)(g + 5.66d), where:

M[sub]p[/sub] = plastic moment capacity of the outstanding angle leg based on a unit (1") width
e* = distance from k dimension (toe of fillet) at back of leg to centroid of loaded area
g = width of bearing seat
d = distance between toe of the outstanding angle leg and toe of the inside of the fillet (angle leg width minus k dimension)

To apply this equation you, of course, need to include an appropriate factor of safety and combine the transverse bending stresses with the longitudinal flexural stress present in the beam bottom flange. A recommended procedure is provided in the Galambos paper. The paper is available for free on the AISC website for AISC members and is available for a nominal fee for non-members.

 

[tebodm]

Thanks for the responses, I will check out the additional papers on AISC, of which I am a member.

I've talked with the manufacturer, I do not recall what the safety factor is, but I have seen references that list between 3 and 6 for safety factors for hoist/clamp assemblies. Client is proposing to use 2 of the 15T units, spaced 12' apart. The point load analysis results in the flange being overstressed which is why I am looking to distribute the load over the length of the clamp.

 

[BAretired]

Looks like a perfect application for yield line theory.

BA