l/360 for dummies

[mbyrne]

Re: l/360 for dummies

L/360

30-foot span, divided by 360 = 1-inch of uniform deflection.

or 360-inch span, divided by 360 = 1-inch of uniform deflection.



Joist spacing:

24-inch spacing:
22.5-inches divided by 360 = .0625-inches of concentrated deflection.

16-inch spacing
14.5-inches divided by 360 = .040-inches of concentrated deflection

Use 300-lbs. for weight

[robc-airww]

Re: l/360 for dummies

Careful Magna, loads are usually psf, not psi. The equation you are after is here: http://www.engineersedge.com/beam_be...m_bending1.htm

If you play around with this, you can also figure out the depth of the member needed for a given deflection limit.

also, the best span calculator I have seen is http://www.awc.org/calculators/span/...rcalcstyle.asp

[frenchie]

Re: l/360 for dummies

Hate plug Mike's rival, but... there's a handy calculator over at Bridge's:

http://www.johnbridge.com/vbulletin/deflecto.pl

[magna111]

Re: l/360 for dummies

In reading one of the links provided by Scuttlebuttrp, the author recommended using a laser in the center of the span to mark the wall, then load the center of the span (about 300 lbs) and measure the deflection and compare the results to the allowed L/360.

Well even though I did most of the work myself, I now have a much better understanding of deflection, how to find it and apply it.

Hopefully others more experienced and who have a greater understanding can pitch in and confirm or expand on what I've learned already.

[magna111]

Re: l/360 for dummies

Ok, did a little more research and I think I have most of what I need.

http://www.southernpine.com/spantables.shtml

From that link you can view tables which tell you how much span is allowed to meet L/360 by different variations of grade size and spacing at different loads.

So given the above example and 30psf live load 10psf dead load grade 2 2x6 spaced 16oc exceeds L/360.

I guess at this point all I need to know is how do I determine what my live load and dead loads are for a 1st floor kitchen vs a 2nd floor bathroom in Maine vs in Texas?

*** I will try to answer this myself, but if anyone else beats me to it thank you, and also please correct me if Im wrong with anything above or if you have better links or suggestions on books/charts to purchase vs what I can find free online. As a note I didnt get too much sleep last night so confirmation that all my research thus far will make me feel a bit better about its accuracy. ***

[scuttlebuttrp]

Re: l/360 for dummies

Article from FCI. No formula yet though.
http://www.fcimag.com/Articles/Featu...00f932a8c0____
http://www.fcimag.com/Articles/Colum...00f932a8c0____
http://www.fcimag.com/Articles/Featu...00000000189599 last one. Halfway down next to the pic of the guy using 9235.

[magna111]

Re: l/360 for dummies

Alright, did a little looking and I think I understand the 1st half of my question, which I think I new before but still am unsure how to apply it so feel free to advise me on that, and also let me know if my understanding so far is correct.

L/360 is the length of the unsupported span in inches divided by 360, so for a 10 foot span, L= (10feet x 12inches per foot) so L is 120, 120/360 is 1/3 so the max deflection is 1/3" for that span.

Now to the second part of my question, how do I apply that to my joist size and spacing, or where can I find a chart or calculator that tells me how much deflection a particular species of a certain size joist will have over any given unsupported span.

[scuttlebuttrp]

Re: l/360 for dummies

I know I've seen a formula a long time ago but since 99% of my work is on grade I didn't pay attention at the time. Now I'm seeing more older remodels and simply use the Deflecto calculater.