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can i neglect deflection?

can i neglect deflection?

can i neglect deflection?

(OP)
if my monorail on the cantilever is failing in deflection which i know wouldnt affect the serviceability of the monorail in the field, deflection is 0.5 in for 6 feet cantilever.

can i neglect it?

all other check beam passed including bottom flange bending.

thanks,

RE: can i neglect deflection?

No Codes mandate absolute deflection limits, they only recommend relative limits to prevent serviceability isses, like cracked plaster.  I would say you can use your engineering judgement to come up with a reasonable deflection limit in this case.  However, deflection of the beam may not be the only issue.  Though you say you have checked everything else, I would be careful to be sure the beam is stable at the cantilever.

I am assuming this is a crane beam.  Will the customer be happy with his load bouncing up/down a fairly large amount?  I could definitely see getting fine vertical positioning to be difficult, if the beam is too bouncy, as they start/stop the winch.  I have experienced this personally, on an overhead crane that had somewhat jerky on/off control.  The load could easily bounce +/- 1/4", which made setting it down accurately very difficult.

RE: can i neglect deflection?

Agree w/Sguy above.  

I am in an area where we are allowed designs that go to L/60!!  While it sure gives us some design leeway - walking on such structures really heights the "pucker" factor.  So we try to avoid it or at least dampen it.

RE: can i neglect deflection?

This is effectively L/72.  

Personally, I would try to limit it to around L/300 (About 1/8"), but that's just me.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: can i neglect deflection?

(OP)
thanks.

i dont think it would be a problem in my monorail. it's just a few feet high and they will just use it once every year or few years for equipment maintenance.

RE: can i neglect deflection?

For a cantilever, I calculate deflection based on the cantilever span * 2.  My argument here would be a beam cantilevering 15 feet should have the same allowable deflection at the tip, as a 30 foot long beam, supported at both ends, would have at mid-span.  So by my argument, his deflection would only be L/288, not quite so scary as L/72.  And besides, wouldn't his deflection (1/2" in 6 feet) be L/144, not L/72, just based on the cantilever span?

RE: can i neglect deflection?

Structuresguy:

Yea, you're right.  I do the same thing.  It's Monday, what can I say?

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: can i neglect deflection?

Ahh, another attach of the Mondays.  I never want to buy anything that was built first thing Monday morning, or last thing Friday afternoon.  :)

RE: can i neglect deflection?

Also, if this is the end of the crane run then would the actual track go all the way to the end?

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