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RE: post-tensioning

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Jojo,

-Typical P/T Construction Span Depth Ratios:

Continuous		Simple Span
Roof	Floor		Roof	Floor
One-Way Slab	50	45		45	40
Two-Way Plate	45-48	40-45		---	---

Note that these are merely suggested typical ratios, and not mandated by Code. They do usually provide satisfactory deflection performance 

-There is no Code required percentage of DL to balance. However, 75% is typically a good starting point. The only requirement is that the service level stresses resulting from the axial compression, primary and secondary loads due to prestress and applied dead and live load moments remain below allowable stress limits. Stresses are checked at application of prestress and under design loads. Usually, we design the level of prestress and slab thickness based upon achieving desirable stress and deflection requirements and then verify adequate ultimate strength. Any required additional strength is achieved by adding mild steel. Shear typically doesn't  influence the design for one-way slab systems, but of course MUST be checked.

- If you would like to forward your design criteria (no. of spans, span lengths, loading, etc.) I'd be happy to offer suggestions.


-Also, FYI, the PCI (Precast/Prestressed Concrete Institute) does not write any Code and is primarily concerned with the design, manufacture, and application of structural and architectural precast concrete and GFRC, glass fiber reinforced concrete. The PTI (Post-Tensioning Institute) spun off from the PCI in the 1970's and is a separate organization. It doesn't author any Code either. Both organizations publish design recommendations, design examples and guide specifications.  For the PCI, it's the PCI Design Handbook (MNL120-92, 4th Edition). For the PTI, it's the Post-Tensioning Manual (5th Edition).  These materials are copywritten, so I can't forward (and they're hundreds of pages long). You can order directly from PCI or PTI.

PCI has a website:    http://www.pci.org/

PTI
1717 West Northern Avenue
Phoenix, AZ 85021
(602) 870-7540

-The applicable design provisions for prestressed concrete are found in ACI318-95 which is essentially regurgitated as chapter 19 of the Uniform Building Code.


Hope this is a start of answers to your questions.

Regards,

Brent Koch, P.E.
Livermore, CA


-----Original Message-----
From:	jojo see [SMTP:jsee98(--nospam--at)yahoo.com]
Sent:	Sunday, February 22, 1998 5:20 PM
To:	seaoc(--nospam--at)seaoc.org
Subject:	post-tensioning


hello there !

A. is there anybody who could  help me check latest
span / depth ratio limits of one-way flat plate floor slab? ( for
simple and continuous spans)

B.is it true that 75% DL of post -tension (unbonded) must be
considered for the above mentioned data.
was there any changes based on latest PCI codes?

C. pls. attached PCI codes if possible.

ty in advance

jojo see

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