low-lax vs stress relieved prestressing strands

huangyhg

low-lax vs stress relieved prestressing strands
does anyone have an idea when low relaxation prestressing strands became available?
i have to determine the strength of some old hollow core plank that were made in 1971, but the precaster is now out of business and i would like to get an idea of what was done back then.  
i know the difference between the two is pretty big in terms of losses so i definitely feel this is pretty critical.   
i think your best bet might be, if you are in the u.s., to contact a local "flexicore" or "spancrete" manufacturer.  while they may not have a competitors load tables, they may have the code and design data from way back then.
structuraleit,
i first got involved in prestressing in 1976 and low relaxation strand was still not available in australia then if i re  
if this is critical, do a load test on one of the planks against deflection.  the type, size and quantity of tendons will only give you a small part of the picture.  additional losses due to relax vs relieved after 37 years will have little effect (less than 1% stress loss on tendon).
pick the longest plank, cut its side connections and fill a large bag full of water at the center of the span (you will need to know the final weight - 15 psf over the middle third should give you a decent result).  monitor the deflection change and extrapolate the plank properties.
final step - write a report for publication with lots of pictures.