# Maximum deflection in a timber beam

1. Oct 1, 2009

### nick.w

1. The problem statement, all variables and given/known data
Particle board flooring (dead load 8 kg/m2 including joist self-weight) is supported by a series
of Radiata pine VSG8, of call size 150 x 50, timber joists running parallel to one other at 450
mm centers and spanning L=3.8 m between supports. The floor supports an imposed load
of 3.5 kPa.
http://img14.imageshack.us/img14/7767/timbertable.png [Broken]

Assuming strength requirements are OK (they may or may not be), what would be the
maximum deflection (in mm) of the joist?
Assume allowable deflection for the joist is L/350. Is the calculated deflection
acceptable?

NOTE: for this calculation use w = 1.0 * Dead + 1.0 * Live
(use gauged, kiln dried section size for timber section)

2. Relevant equations

Max Deflection = 5wL4 / (384EI)

For the above formulae:
L is the length of the beam,
E is Young’s Modulus (Units Pa, MPa, GPa)
I is the Second Moment of Area of the cross-sectional shape of the beam (units m4 or mm4)

3. The attempt at a solution

I think this is the correct formula but need to be certain. Also how do I find "I" if this is the correct forumla.

I also get thrown off by. "use w = 1.0 * Dead + 1.0 * Live" as I have already calculated the UDL in an earlier part of the question using w= 1.2*dead + 1.5*live.

If you guy could point me in the right pirection of which formula to use I would appreciate it.

Regards,
Nick

Last edited by a moderator: May 4, 2017
2. Oct 1, 2009

### nick.w

edit: Just been having a flick through the forums and wondering if I might of put this in the wrong place. Please move if so. Cheers

3. Oct 2, 2009

### nick.w

bump? More info needed?

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