beam deflection L/360
beam deflection L/360
(OP)
thread507-37706: Allowable Beam Deflection
Hello Everybody after reading the reference thread i just want to figure out the meaning of 360 on the deflection parameter, where this number came from? it has any units? if my deflection calculations are in metric units i use the same value? what are the conditions to compare this parameters... i undestand that in imperial system the value of L must be in inches, what about in metric?
thanks a lot for any comments.
Hello Everybody after reading the reference thread i just want to figure out the meaning of 360 on the deflection parameter, where this number came from? it has any units? if my deflection calculations are in metric units i use the same value? what are the conditions to compare this parameters... i undestand that in imperial system the value of L must be in inches, what about in metric?
thanks a lot for any comments.






RE: beam deflection L/360
Some of the other deflection limits are also set by the type of finish applied to the member. Brittle finishes need tighter deflection limits to prevent cracking etc.
RE: beam deflection L/360
All it means is that you are limiting the vertical deflection to 1/360th of the span of the beam, a common limitation for sheetrock and plaster ceilings to limit cracking of the joints.
Mike McCann
MMC Engineering
RE: beam deflection L/360
RE: beam deflection L/360
Recently, a senior colleague told me that he feels that L/XXX is intended to limit the maximum slope occurring along a member for occupant comfort. I'm not sure that I buy it but it's a novel take on it.
At roofs, of course, there is ponding to consider.
When I've been aggressive with deflection limits, I sometimes wonder about the impact of movement on my connections. Is a single plate shear tab still a moment free thing with end rotations commensurate with, say, L/90 deflection? I'm not sure.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: beam deflection L/360
If you are working to a specific figure, you need to establish whether it is just under imposed load, or imposed plus dead load
RE: beam deflection L/360
It is probably more rate of change in slope that is being limited, so curvature as you first suggested.
RE: beam deflection L/360
Some of us in metric countries have adopted L/250 and L/500...
RE: beam deflection L/360
... but it will resonate around 4Hz, which they will describe as 'a little bouncy' when they dance on it.
Mike Halloran
Pembroke Pines, FL, USA
RE: beam deflection L/360
Yep, I always assumed the same. With the span measured in feet and the deflection measured in inches L/360, 240, 180 become L/30, 20, 15 respectively.
It's similar to the reason concrete compressive strength is measured at 28 days: that's divisible by 7 so the testing cylinder break won't have to occur over a weekend.
RE: beam deflection L/360
Keep in mind these are minimum and there are many reasons to have stricter deflection limitations.
RE: beam deflection L/360
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