Low-Lax vs Stress Relieved Prestressing Strands

[Lion06]

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.

 

[jheidt2543]

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.

 

[rapt]

StructuralEIT,

I first got involved in Prestressing in 1976 and Low Relaxation strand was still not available in Australia then if I remember correctly. It was introduced over the next few years but both were available for a while.

I do not know if it was earleir in USA.

 

[Teguci]

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.