Prestressed Double Tee Floor

[sandorfla]

I am trying to evaluate (for proposed loading) 14” double tee floor sections on an existing laboratory built in 1965. A Louisville,KY local firm, Dolt & Dew (which is out of business) fabricated them. I have searched the load tables in the 1971 PCI handbook but cannot seem to find any double tees that match the dimensions that we have. I have the shop drawings but the design loading/strand details etc. are not specified. The width is 5'-8",the center to center of the webs is 34" and the end to center of webs is 17". Can anyone suggest where I might find these very old load tables? Thank you.

 

[JAE]

Even if you find load tables for that section, you won't know the amount of tendon reinforcement anyway, correct?

The only thing you can do is either so some sort of exposure of the tendons (which I wouldn't recommend for fear of damaging them), or some type of X-ray system (which I'm not familiar with) or a load test.

I once did a load test for some double tees used on a grandstand using water barrels and following ACI 318 and the IBC.

You would need to create some shoring system to alleviate the danger of the load test over-loading the tees to avoid a collapse. Deflection monitoring would be required to determine the elastic spring-back per ACI.

 

[Ron]

I agree with JAE...a load test would be indicated in this case. You cannot likely replicate the design without a lot of expense and effort. You can use radiography to show the tendons in the web and flange, but would take multiple shots with the radiographer knowing something about concrete (for instance, radiography with concrete results in an object to film distance greater than what most industrial radiographers typically deal with. For weld radiography, the object to film distance will be typically less than an inch; whereas, for concrete, it might be several inches....this can lead to erroneous assumptions of strand or rebar size)

Load testing would be the proper way to go for evaluation. I would not recommend using barrels as they do not allow sudden release of the load in the event of impending failure. I would construct a baffled pool with a plywood frame and a membrane to hold the water (6-mil poly works fine). You can build a safety feature into this that allows you to suddenly drop the load on the system in just a few seconds....critical for failure prevention.

 

[JAE]

Ron,

When you say "baffled pool" you are indicating a pool that is divided up into smaller pools so that when the framing members deflect, the water doesn't rush to midspan - correct?

 

[Ron]

JAE...that's correct. It is to keep the water level relatively constant over the span. It make the sudden "ditch out" a little more difficult, but prevents progressive overloading.

I have used this on relatively large load tests (40x40 bay in parking garage)...it works fine.