Transfer length for pre-tensioned

[Ilight]

Hey everyone:

Let's take 12.7mm low relaxation strand for example, in the PCI code, for effective prestress at transfer, they have adopted 170ksi which roughly equates to (0.75*270)*0.85, assuming the total losses are 15%. However on the second graph, the effective prestress they've taken is 1040 Mpa, which is roughly (0.75*1840)*0.76, assuming 24% total losses. (Sorry for the mix in units)

So my question is that, with different losses being considered in the design, sometimes we may obtain values that are higher than the effective prestress shown on the diagram, does that mean the transfer length should be extended beyond the limit shown on the graph? (I know there's also the development length that comes after, but let's consider only the transfer length).

 

[Ingenuity]

Yes, with an increased effective prestress, the transfer length will increase.

The PCI Figure 4.12.4 that you show is simply a plot of the ACI 318 equations:

 

[rapt]

Yes, you should calculate the losses for each situation rather than use a nominal value as is used in that diagram.