This section describes how the maximum jacking forces for prestressing strands is computed.

The jacking force is computed as

where f_pj is the jacking stress and A_ps is the total area of prestressing strand.

Jacking Stress - 1st Edition

The jacking stress is prescribed in Article 5.9.3 of the 1st Edition of the LRFD specification. The jacking stresses are

for Stress Relieved Strands and

for Low Relaxation Strands.

Jacking Stress - 1st Edition with 1996 and 1997 Interim Provisions to 3rd Edition 2004

The 1st Edition with 1996 and 1997 interim provisions change the method by which the allowable jacking stress is to be computed. Article 5.9.3 specifics the strand stress immediately prior to prestress transfer as

for Stress Relieved Strands

for Low Relaxation Strands.

The jacking stress is

Substituting, we get

NOTE: From now on, we will only deal with the stress relieved strands. The formulation for low relaxation strands is similar.

From LRFD Equation 5.9.5.4.4b-1,

Substituting and re-arranging, we get

This equation is solved for f_pj

Jacking Stress - 3rd Edition 2004 with 2005 Interim Provisions and Later

AASHTO removed the computation of relaxation loss prior to prestress transfer with the 2005 interim provisions. The jacking stresses are

for Stress Relieved Strands and

for Low Relaxation Strands.

WSDOT retained the computation of relaxation loss prior to prestress transfer. The method for compute the maximum jacking stress is the same as described above however WSDOT uses the term

in the equations.