Wood Floor Joists Reinforcement
Wood Floor Joists Reinforcement
(OP)
Been reviewing an existing building second floor structural system to accommodate new (increased) occupancy loading. Present floor framing is 2 bye wood joists, which are, by the numbers, incredibly overstressed for the current occupancy. Thinking of "Sistering" each joist with cold form metal joists designed to handle the total imposed loading (anticipated + existing dead load plus new occupancy live loading) to simplify things. Anyone have any thoughts or words of wisdom?
My rational is to: 1)Keep connections simple between the wood & steel (only that required to transfer shear and provide stability), 2) Design the new metal joists one size smaller in depth than the existing wood joist - to not have to worry about floor squeeking and facilitate installation, 3) Not clutter up the first floor by installing new footings, columns and girders and, 4) Give a warm fuzzy feeling knowing the system will work no matter what.
My rational is to: 1)Keep connections simple between the wood & steel (only that required to transfer shear and provide stability), 2) Design the new metal joists one size smaller in depth than the existing wood joist - to not have to worry about floor squeeking and facilitate installation, 3) Not clutter up the first floor by installing new footings, columns and girders and, 4) Give a warm fuzzy feeling knowing the system will work no matter what.






RE: Wood Floor Joists Reinforcement
RE: Wood Floor Joists Reinforcement
RE: Wood Floor Joists Reinforcement
If new cfs are not tight to the underside of deck, you have kind of a flitch plate situation.
If no circumstances preventing you from using cfs between existing joists, why not?
Consider reviewing install procedure with contractor.
RE: Wood Floor Joists Reinforcement
You can design the floor as a 'stressed skin panel', assuming that the decking material to the top surface of the floor acts compositely with the timber joists. Is this possible for your application?
Another approach would be to reduce the span of the existing joists by introcucing a beam support towards mid span.
VB
RE: Wood Floor Joists Reinforcement
RareBug
RE: Wood Floor Joists Reinforcement
I like your idea and see no problem with it how it works.
If you can get bearing at each end of new cold formed sections then the wood joists are nominally redundant and only provide restraint. All is well - simply fix the cold formed to the timber at reasonable centres such that the load transfer can occur through the fixings rather than by bearing. Make sure the bearings are well shimmed to transfer the loads onto the walls. The existing floor will probably have also deflected so you may need your reduced section just to get the new (straight) members into the space.
If you can't get proper bearing at each end then the forces can usually be transferred back into the timber by multiple fixings at the ends of the steels. This is the alternative to the flitched beam described elsewhere - here there are two steel plates with the timber in the middle. - It's still a flitched beam and the design process is the same.
RE: Wood Floor Joists Reinforcement
RE: Wood Floor Joists Reinforcement
I think the idea is that the new cold formed joists take the full load. The timber joists are thus not required as joists in the final solution but are simply packing.