can i neglect deflection?

[delagina]

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,

 

[structuresguy]

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.

 

[MiketheEngineer]

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.

 

[msquared48]

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

 

[delagina]

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.

 

[structuresguy]

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?

 

[msquared48]

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

 

[structuresguy]

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

 

[csd72]

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