I strengthened a floor by adding a 2 x 4 to the bottom of some floor joists
in a manner similar to the bottom flange of an "I" beam. I glued it with
construction adhesive and screwed it about every 6-8 inches. I ran the
stiffener from support beam to support beam. Wish I had done the entire
house rather than just the kitchen.

There was a study done several years ago concerning the use of solid vs "X"
brace blocking, and several alternatives. The researchers determined that
the best way to stiffen a floor was to use solid blocking between the
joists, nailed tight, and then to install a very strong continuous strap
pulled tightly across the bottom of the joists directly under the blocking
and nailed in place. The effect is to distribute the load between joists.
The problem found with normal X brace blocking or even solid blocking is
that the tension in the bottom chord of the blocking causes it to pull away
from the joist so that the blocking depends upon the compressive strength of
the blocking installation only. The metal strap pulls everything together
and transfers the tension across the joists. While I know that you indicated
that your abode uses trusses, I'm sure that you could make the idea work.

I think this research came from the Canadian Building Code council (or a
similar Canadian organization), but couldn't seem to Google up anything. I
have probably filed the article away, and will see if I can resurrect it
from the archives later today.

Jim Ray, President
McFeely's Square Drive Screws
www.mcfeelys.com

"Dan Oelke" wrote in message
...

In my current abode they used floor trusses for both the first and
second floor. From the basement I have easy access (for now) to the
first floor trusses. They are great in that they allow for such a long
span and a very open floor plan. However - there is a fair amount of
bounce in the floors, especially when two kids get a little excited
running around the house. This is especially true in the kitchen area
which has cabinets all around, heavy appliances, island, etc. so I
suspect that this added "normal" load makes them a little more flexible.

Does anyone have any suggestions for how to stiffen or strengthen these
trusses? There is currently one strongback going across the trusses
about mid-span between the supported ends. This isn't something that I
am afraid has been under-engineered to start with. From my reading of
some span tables, etc the spans are well within what they can be for
that size of truss. I'm just looking to reduce the rattling of
glasses/light fixtures, etc when the kids go jumping.

Some ideas I have had a

1) Add additional strongbacks. How big is useful? Would a 2x6 do much
or do I need a 2x10 or 2x12 before it does any good? Going around
heating ducts and drain lines could prove somewhat a challenge to get
bigger sized material in place.

2) Put in some kinds of cross-bracing between the trusses - like you
normally see for normal joists. Allows for easier maneuvering around
utilities. This of course begs the question - wood or metal.

3) Add plywood gussets on the truss sides where I can. Because of
heating ducts, plumbing, etc, there are some places that I couldn't, but
most places I could. Does it help/hurt to only do this on one side? Do
the extra fasteners into the 2x4's hurt their strength?

4) Do some/any of the above after jacking up the center of the truss by
a small amount (1/4" ??) so that the re-enforcing is taking the load
right away.

Any other brainstorms?

Thanks - Dan