[floorman41041]

Am pouring a 7.25"x30'x48' 4500psi foot suspended floor. Perimeter is 4000psi @8" wide concrete with an 8" wide concrete dividing wall Centered at 24' on the 48' splitting the 48' into two pads spanning effectively 28.625'x23'. Concrete is re-enforced with #4 rebar at 4 foot intervals around perimeter and across middle wall welded to vertical rebar in walls and at every junction within the rebar "mesh". Wire mesh panels 5'x10' were also included. Underneath floor is supported by double 2x12s capped with 2x4 on top and bottom on 16" centers with 3/4" advantec on top of the joists. The joist span the ~23' side. The wooden floor joists and advantec sits on double 2x12s on all four sides of each pad which is anchored into the concrete walls with 3/4"x8" anchor bolts every 3'. I have cross braces under each joist which are triple 2x6s supported by 20,000 lb screw jacks spaced every 6 ft. The pour went OK and nothing came down. Will I need to leave any jacks supporting the basement floor or with it stand unsupported and what weight load will it hold in the center of the 28.625x23' pad?

[ma0641]

Love to help but, was the floor pan formed? Designed for post tensioning? Although there are a lot of competent people on this sight, I believe you are well into the structural engineering domain. Was this job permitted? Who did the design? It seems a bit late to be asking these questions.

[smearcase]

The weight of the load to be supported is the first step of this type design calculation in my experience. I agree with ma0641.

[floorman41041]

Using formula FBd^2 / 9L The pad will stand disregarding strength of concrete.
F 1440
max load n lbs = FBd^2/9L
L 22.625
F=strength of wood
B 3
B=breadth of joist (thickness 2x12=1.5, doubled = 3)
d 11.5 (std is 11.25 but used 11.5 considered capped 2x4)
d=depth of floor joist (actual width 2x12 = 11.25) joists 22
571320 FBd^2 2x12+capped with 2x4 use .3 of thickness of 1.5 due to orientation of forces
203.625 9L
2805.745856 lb wt per joist
1.333 joist spacing in feet (16" = 1.333ft)
22.625 span length in feet
30.159125 joist area
93.03140779 wt per joist sf 22 #joists
61726.40884
644.8125 sf of unsupported area
0.604166667 150 per cf*7.25/12
90.625 .604167*150
58436.13281 wt of concrete floor@150 cf
61726.40884 wt rating of floor joists
3290.276027 margin
5.102686482 wt rating in center of pad So if concrete turns to chalk the floor will hold it
"barely"

[ma0641]

I guess then, what more could we add if you have all the design data?

[floorman41041]

I agree! Then the purpose is to communicate one needs to know all the design data of the perimeter, the weight load, one needs to get permitted, one needs to get competent structural engineering for design of complex questions. This 1st pass by a novice was improved by adding cross beam supports to each end of each "pad" and one in the middle to reduce spans to ~11ft and still allow max unstricted "open" areas rather than centered on "wants" alone. If build, it would now support the proverbal "mack" truck. By the way the F is based on beam strength tables for Southern yellow pine joists...