A 32Æ-0ö wide building. The floor
A 32Æ-0ö wide building. The floor
(OP)
Trying to find a soution for excessive floor deflection.
A 32’-0” wide building. The floor structure is 4”x10” Hemlock joists, 4’-0” on center with a 2x6 tongue and v-groove southern yellow pine decking. There is a center girder, effectively reducing the span to 15’-2 ½ ”.
Originally, the floor system was supposed to be designed to support a 50# per square foot load. After I noticed the excessive deflection, almost 1 inch on some joists, we looked back at the design and determined that we had a communication problem and undersized the joists (probably should have been 8x10’s or 6X12’s)
One thought is a steel strap support on the bottom of each joist. By lagging the strap at each end of the joist, then by using a bolt and threaded tube assembly at the mid-point, force the strap away from the bottom placing the joist in compression and the strap in tension. I expect this to eventually persuade the joists back to level.
I would like to read some expert opinions regarding this method. Then if possible, calculate the loads, appropriate size strap, bolts, and fastening so I can get them fabricated.
Of course I’m open to other ideas.
A 32’-0” wide building. The floor structure is 4”x10” Hemlock joists, 4’-0” on center with a 2x6 tongue and v-groove southern yellow pine decking. There is a center girder, effectively reducing the span to 15’-2 ½ ”.
Originally, the floor system was supposed to be designed to support a 50# per square foot load. After I noticed the excessive deflection, almost 1 inch on some joists, we looked back at the design and determined that we had a communication problem and undersized the joists (probably should have been 8x10’s or 6X12’s)
One thought is a steel strap support on the bottom of each joist. By lagging the strap at each end of the joist, then by using a bolt and threaded tube assembly at the mid-point, force the strap away from the bottom placing the joist in compression and the strap in tension. I expect this to eventually persuade the joists back to level.
I would like to read some expert opinions regarding this method. Then if possible, calculate the loads, appropriate size strap, bolts, and fastening so I can get them fabricated.
Of course I’m open to other ideas.






RE: A 32Æ-0ö wide building. The floor
If at all possible consider breaking the span with another girder. A strap in tension may seem a simple solution, however, the connections may prove to be a major and complex problem.
RE: A 32Æ-0ö wide building. The floor
RE: A 32Æ-0ö wide building. The floor
RE: A 32Æ-0ö wide building. The floor
I'm afraid it may be impossible to remove all the deflection. If possible scab 2x10 or 2x8's to the existing 4x10's then figure what you need in addition. Maybe 2x10 or 2x8 at 16" or 24" o.c. between the existing 4x10's.
The structure you describe sounds like it was meant to be exposed. What I described above is not going to be as nice looking as the beams at 4'-0" o.c. I don't think you are going to get your metal strap/truss idea to work. It's a way out idea and would probably look like hell too.
I suggest reinforcing the joists and adding more and if it is exposed then put some nice bead board on the bottom/ceiling side also.
RE: A 32Æ-0ö wide building. The floor
Boil down the problem by finding out what span your existing joists can safely carry. Then, install supports to cut the span to this length. Obviously, this will clutter the area below this floor but if not a problem, this is your most cost effective way to go.
If it is a problem and you need the space below the floor you will have to scab the joists. I have reversed creep/deflection by jacking the floor system then bolting steel plates/channels to them. 15 foot channels/plates weighing up to 250 pounds each can easily be installed by three men and give you quite a bit of moment capacity. Before installing the steel, I butter the joist with liquid nail, then suck the steel tight (not over tight) to the joist. Let the adhesive cure before jacking down. The floor seldom drops more than a hair.
Another option is to install additional 4 x 10's (or whatever works) in the bays cutting the spacing to 2 feet, 16 inches, etc. However, it is difficult to reverse creep this way and you may not be satisfied with the result.
Sounds like this was done without a structural engineer originally and I would recommend you hire one to design a repair. Let's not spend good money after bad.
RE: A 32Æ-0ö wide building. The floor
I would opt for jacking the existing joists at midspan, inserting intermediate joists (to make the spacing 2'), then releasing the jacks.
I agree...you need a local engineer
RE: A 32Æ-0ö wide building. The floor
The point here is this: as with most floors, deflections and vibrations are the first thing that owners notice and complain about (and rightfully so) as being unacceptable and this point is usually (but not always) reached long before any other structural limits are reached. You seem to be in the same boat but you need to have your engineer do these calcualtions for you and NOT rely on mine. Adding another beam perpendicular to yours at mid-span would seem to be best, but again, you have to have your engineer tell you this. Adding the mid-span beam would effectively mean that your 15 ft beam now spans 7.5 ft. Deflections (for this same load) go down by a factor of 8 to about 0.125 inches and stresses are cut in half. Good luck, and again, this is NOT legal advice....you need to have your engineer check this out.
RE: A 32Æ-0ö wide building. The floor
Ken
RE: A 32Æ-0ö wide building. The floor
If you are out of your area of expertise then you should hire a local structural engineer.
RE: A 32Æ-0ö wide building. The floor
oh snap!