Development Length Prestressed Concrete

[jreit]

I'm trying to find if there's a design formula to calculate the development length of reinforcement in prestressed concrete.
ACI 318 wasn't very useful but it seems geared towards CIP. I don't have access to the PCI manual, but would it have information regarding this topic?

 

[KootK]

From ACI 318-11:

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[rapt]

Are you talking about development length or prestressing steel or reinforcing steel? KootK has given the clause for pretensioned strands, but I read your question as being for normal reinforcing bars.

 

[asixth]

Development length of reo should be the same whether the slab is prestressed or not.

 

[jreit]

Thanks for your replies regarding the development length.
I haven't much experience with prestressed concrete but the terms transfer length and development length are almost used interchangeably.
Are they the same? They seem to both refer to the length needed for the steel to achieve full yield stress when bonded to concrete.

 

[rapt]

No, they are different for prestressing strand.

Transmission length is the length the force is transmitted over at transfer when the pre-tensioning strand is released to transfer force to the concrete through bond. Normally the stress in the strand over this length is not assumed to increase under strain.

Development length is the total development length under strain.

This is shown diagrammatically in the Commentary in R12.9.2.

 

[wijgeng]

I am also curious which reinforcement you are talking about developing. KootK described the development of prestressing strand. I am not sure what effect prestressing would have on longitudinal strand. I expect that prestress does improve anchorage of shear reinforcement though (because the prestress acts to "pinch" the anchored stirrups. My master's research was on this topic at the University of Minnesota.