cantilevered beam deflection limits vs. simple span beam

[Backcheckrage]

G'day people.

Random question: why is the deflection limit for cantilevered beams typically twice that for a simple spanning beam?

For example, deflection limit for a simple spanning beam would be say L/400 and for a cantilevered condition it would be 2L/400 (L/200). Why would the cantilevered condition be more relaxed? I would think humans would more easily perceive a change in floor elevation over shorter distances, so I would think it would be more stringent for cantilevered case.

I've been using the "2L" rule for setting cantilevered beam deflections, just never understood why -maybe the community can help.

Any insight would be much appreciated!

Cheers

 

[rb1957]

could it be that the cantilever is being considered as 1/2 a SS beam ?

wonder if the convicts will beat out the darkness for this years' bledisoe ?

Quando Omni Flunkus Moritati

 

[Planet3]

How about looking at it as 2 cantilevers, opposite directions, from the same wall support.
Think of that with simple supports at each end and no wall in the middle.
You have slope and deflection at each end. No slope and no deflection in the middle.
Length of the simple span is two times the cantilever length with the same deflection.

Great question.

-MCW
(KY)

 

[dhengr]

Obviously, none of you guys are diving board designers or builders.

 

[msquared48]

Only half-wits jump off cantilevers. That's why the limits are doubled.

Mike McCann
MMC Engineering

 

[wannabeSE]

I think the 2L/xxx limit is for the displacement at the free end of the cantilever ([Δ]) rather than a measurement of deflection (or curvature of the beam; [δ]). Honestly, I think engineering judgment and coordination with other disciplines is more important than the building code requirements when it comes to deflection. I treat the building code limits as a guideline and starting point when considering deflection.