1950s bldg - precast double tee capacity

huangyhg

1950's bldg - precast double tee capacity
i'm looking at a precast double-tee roof structure for a bldg constructed in the 1950's.  the owner wants to add additional load on the roof and does not have plans for the bldg nor could i find any markings in the field that would distinguish a manufacturer.  what kind of procedures if any could i follow to determine the members capacity?
tia
i think, this is really tricky.  depending on design requirements, a same size dt may may different number of strands.
to find out the exact quanty of strands, try to perform non destructive testing like gpr, etc.  to find out actual concrete strength, take some cores from the actual   
add small increments of load at midspan and measure deflection.  by assuming e, calculate i.
civilperson-
how would this tell you anything about capacity?
check out aci chapter 20, section 20.3 for in place load testing.  this may take some effort but may be way more reliable than cutting, chipping, or x-raying the dt to "sorta" know what it is made of.  it also may actually be less expensive than ndt and structural analysis.