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Re: Development Length for Prestressing Strand

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At 12:47 9/11/99 -0800, you wrote:
Does anyone know the development length requirements for an untensioned prestressing strand?  Are there any references that address the topic?

This is a very difficult one. Most codes give values for stressed strands that are then released as in pretensioning.
Unfortunately, when the strand is untensioned at the time of casting the concrete, and then loaded, it reduces significantly in diameter due to the loosness of the stranding, much more than the reduction in diameter of a solid bar under load. Because of this, it is not possible to use the usual bond approach to the calculation.

I have done testing on this and found that a .5" strand will not hold with 3ft of bonded length. The worst part was, after slippage started, only a small fraction of the "bond" remained and the strand slipped out relatively easily. Because of this, I would always recommend the use of a anchorage of some sort to achieve bond such as a bonded swaged deadend type anchorage.

Regards  Gil Brock
Prestressed Concrete Design Consultants Pty. Ltd.
5 Cameron Street Beenleigh Qld 4207 Australia
Ph +61 7 3807 8022              Fax +61 7 3807 8422
email:  gil(--nospam--at)rapt.pcdc.com.au
webpage:        http://www.home.aone.net.au/rapt.pcdc/