Anchorage set losses

Anchorage set losses are caused by the movement of the tendon prior to seating of the wedges or the anchorage gripping device. A common value of these losses is about 10mm (AASHTO LRFD 2007).

If \Delta_a is the anchorage slip and L_a is the length along the tendon affected by the anchorage slip (Choudry 1986), then:

\Delta_a = \int_0^{L_a} \Delta_{\epsilon} dx

where \Delta_{\epsilon} is the decrease in the tendon strain due to anchorage slip.

Uniform distribution of anchorage losses
Assuming that the anchorage slip losses are uniformly distributed over the entire length of the tendon (in other words \Delta_{\epsilon} is constant), then the following equations can be written:

\Delta_a = \Delta_{\epsilon} L

\Delta_{\epsilon} = \frac{\Delta_a}{L}

Noting that

\Delta_{\sigma} = E_p \Delta_{\epsilon} and \Delta F = A_p \Delta \sigma

we can write the final equation for the loss of prestress force:

\Delta F = A_p E_p \frac{\Delta_a}{L}

where:


 * A_p ... area of the prestressing tendon
 * E_p ... Young's modulus of the prestressing tendon
 * \Delta F ... loss of prestressing force
 * L ... length of the tendon