We just completed the construction of our new house (did all work
ourselves).

All floors are constructed with 2x10 joists at 16" OC, with 3/4" OSB
subfloor, and solid blocking every 8' of the span.

The floors feel quite solid throughout the house, except in our living room
where the floor is a bit bouncy. The span there is about 15' from sill to
sill, just about the max for 2x10 Doug Fir joists.

We have the same 15' span in our master bedroom and the floor there is
quite solid, so I suspect the problem is due to our large entertainment
center (a few hundred pounds I'm sure) that sits about mid-span in the
living room.

Since the house is single story over a crawlspace, I decided to add a beam
mid-span to stiffen up the living room floor under the entertainment
center.

I used two 2x8 x 10' boards screwed together for the built-up beam. I
supported the beam on three posts, spaced about 4' apart, which rest on top
of concrete deck piers. I would have preferred a poured footing, but
getting the materials back to where I need them in the crawlspace was
rather difficult. The deck blocks seemed like the easiest approach, and I
spaced the piers four feet apart to minimize the load on each pier.

The floor had sagged about 1/2" where we have the entertainment center, so
I used an automotive floor jack to jack the beam up level and tight against
the floor joists.

Everything went rather smoothly, and should have effectively reduced the
span to about 8' on each side of the beam.

Unfortunately, when I climbed out from under the house and came in
expecting the bounce to be gone, I discovered the floor still bounces...
Not as bad, but it is still significant.

So, now I'm wondering what went wrong and what I do now.

The beam should have made the floor quite solid, and yet it still bounces?
The ground in the crawlspace is quite firm, so I don't think there is any
"give" to the piers.

This weekend I'll probably have my wife bounce the floor from above while I
climb underneath to see if I can discover anything. But, I'm interested in
hearing comments from others with similar experiences.

Thanks,

Anthony