what is the capacity of my ceiling joists

huangyhg

what is the capacity of my ceiling joists?
i have an 1890 historic building that i have to update the ceiling with 2 layers of 5/8" drywall.  i have 2x12s' spanning 24 feet on 16" centers.  the ceiling is covered with 1/2" toungue and groove pine, the floor above is covered with 3/4" oak flooring.  i estimate the added weight to be about 4.4 lbs/square foot(about 11,000lbs for the entire building).  one end of the joists are nailed to the side of 2x6 studs, the other ends are embedded into a brick wall.  any advice will be greatly appreciated.  
thank you
call a local structural engineer to look at the problem on site.
regards
sc
the nailed end will give you problems.
new info:  i examined the nailed connection and found that a 1x6 is notched into the edge of the stud for the joists to rest on.  i would think this would help prevent any nail slippage.  again any info will help.
thanks
sounds like the building is balloon framed which is a very good way to build a wooden structure. also the compression face of the joists is probably continuously braced by the floor boards. now the details:
1. determine the actual (not nominal) cross-section dimensions of the joists.
2. determine the (approximate) wood species (southern pine?, oak?, redwood?, etc.)
3. make a visual assessment of representative joists' condition (knots?, splits?, holes?, etc.). do certain joist's differ from the typical? take clear photos.
4. do the same for the 1x6 (called a ribbon in balloon framing).
5. per dicksewerrat's advice, try to determine the details (nail size & count, depth of embeddment in the brick wall, etc.) for all connections.
6. compute the joist's moment of inertia & section modulus based on the actual cross-section.
7. compute the dead load per joist by summing the tributary weight of the floor, ceiling, new drywall, and the joist's self-weight.
8. based on joist species, condition, & a wood engineering reference determine the joist's modulus of elasticity, allowable shear & bending stresses. consideration for repetitive members & duration of live load may be appropriate. depending on use, determine an allowable defection (dead load only & dead load + live load).
9. from applicable building code determing required live load (floor & possibly suspended). there may be special consideration for historic structures.
10. perform calculations for shear, bending & deflection. use engineering judgement to gauge the results. again, pay special attention to what is happening at the connections.
11. keep records of all assumptions,calculations, photos, etc. for the time that you will be legally responsible (often 10 to 15 years or more).
sc's advice to call a local structural engineer is worth considering. there as so many variables when working with wood (compared to steel or concrete).