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1970 Prestressed Single Tees

1970 Prestressed Single Tees

1970 Prestressed Single Tees

(OP)
I'm working on an existing building in New Mexico dating to 1970 which has precast prestressed single tees (8ST28) for a roof structure. We are planning some new roof penetrations. How likely is it that the flanges would contain prestressing strands?

RE: 1970 Prestressed Single Tees

very unlikely... precast tees of that era were likely Lin-T's. The geometry of these can be checked against historic information... this should be easily available. Stressing for these was done in a steel bed/form with high strength strand tensioned from the ends. The strand may have been 'depressed' by means of a patterned 'pull down' device that may have created different profiles for the strand. These 'harping' devices would be used to establish the strand profile, but, the strand would be confined to the web portion of the T.

Dik

RE: 1970 Prestressed Single Tees

(OP)
Thank you, dik. That's what I was hoping to hear.

RE: 1970 Prestressed Single Tees

If there is a slab over the Lin Tees, there could be strand in the slab and often non bonded... you might consider using a low energy chipping hammer to cut through any significant topping (ie. 5 or 6 inch thick or more).

Dik

RE: 1970 Prestressed Single Tees

You could also get someone to scan them for reinforcement which will allow you to locate the penetrations to miss the majority of the reinforcement and let you to locate the reinforcement so that you can carefully demo down to them to determine whether they are prestressed or not.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/

RE: 1970 Prestressed Single Tees

(OP)
Our topping is only 2" thick so I don't anticipate any strands there. We may very well do some x-raying.

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