Bounce

Started by Squirl, August 09, 2011, 01:56:07 PM

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Squirl

The building inspector made a few comments to my design.  For the floor I had 2x12's SPF No. 2 spaced 12" O/C spanning 18'8".  I was told "you will need to place some support in the center because you will have bounce."  I looked it up and 2x12's SPF No.2 12" O/C have a deflection of L/480 for 19'-1".  I have agreed with all other changes and recommendations he has made, but I am thinking of sticking to my guns here.  It is not a question of cost. Both 2x12's 12" O/C and 24" O/C options cost the same.  The center beam option simply takes much more labor.

By code does anyone know how "bounce" is calculated?  Will I have "bounce"?  If so will it be excessive? 

archimedes

Was it a suggestion on his part or a demand?
Give me a place to stand and a lever long enough,  and I will move the world.


Squirl

I can't tell.  It started out as a suggestion to go with smaller lumber for the joists.  The side note was I was going to need a center beam because of to much bounce.  I am going with 2x12's for labor savings and cavity insulation, not cost.

Don_P

Deflection is the only "bounce" that is code regulated, if you're within the span tables you have the option of sticking to your guns... choose your battles.

The other bounce is vibration frequency, I've got a calc from VA Tech for checking it, unfortunately my online calcs got hacked but if it is of interest I can check it, this is non code. As we've been going long, especially with low mass floor systems like TJI's, annoying vibration has become an issue. A joist on a girder is subject to the combination of vibrations of the girder and joist.

Squirl