p.t. concrete 1

[ajk1]

Given:
Existing 2 span post-tensioned (p.t.) garage floor beams with corroding unbonded tendons in the old push-thru sheaths, about 35 years old.
Can not reliably replace the tendons because of various reasons (such as the "pinching effect" where transvers p.t. girders cross, criss-crossing of tendons in the beam, etc. We tried over the years!

Required:

Assume all the existing p.t. eventually fails.

Question:

Can externally installed Dywidg straight bars, 2 near the top of each 2-span beam (just below the slab soffit) and 2 near the bottom of each beam (just above the beam soffit) that are then prestressed to apply the same magnitude of exial force as the existing p.t. in the tendons, be acceptable, if calculations show that the new Dywidag bars apply enough force to keep the entire T-beam section (slab and beam) in compression?

 

[Ingenuity]

Here is another reference for a external PT project in downtown Indianapolis. It was presented at the 2013 PTI Convention in Scottsdale.

It has some similarities to your project: 40+ years old, parking garage, severe corrosion to existing PT (button-head system), and the beam spans are 2 @ 52'. The solution used 8 x 0.6" dia 7-wire strand.

External Post-tensioning Repair of a Parking Structure with Limited Access by Moser and Stanish: ==> Link​

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[KootK]

I suspect that somebody may have already passed this on to you in a previous post but, in case not, here's an excellent VSL guide on external post-tensioning: [link Link

http://freeit.free.fr/VSL Technical Report/VSL Technical Report - PT External .pdf

]Link[/url]. It's a little dated. They cover the Pier 39, San Francisco case study which is where my mind always goes first on this. As a younger and less dignified individual, local SF authorities reprimanded me for public urination in that structure. In my stupor, I looked up at the overhead structure and thought "Cooool!". I think it's the handiwork of Bijan Aalami's firm.

 

[Ingenuity]

...Pier 39, San Francisco case study which is where my mind always goes first on this...

Mine too.

Here is a brief technical and construction wrap-up from Concrete International from 1988 of what they did back in the late 80's on this project.

2 span, 36" deep beams with 65.5' spans, original PT with corrosion damage:

Innovative Rehabilitation of a Parking Structure by Bijan O. Aalami and David T. Swanson ==> Link​

I do recall VSL stating at the time, that if they did this project over again they would NOT use PRECAST tube/shells to provide fire protection to the tendons.


ajk1: So if you 'dig' around a bit I think you will find many, many examples of where external PT has been done on building structures in North America.