Precast concrete NU girders have been used in Alberta Transportation bridges since 2001 with
spans ranging from 30 – 65m. These bridges consist of pre-tensioned NU girders which are
typically post-tensioned in the field for longitudinal continuity. It is standard practice in Alberta to
utilize deflected strands as well as debonded strands to minimize stresses at the ends of these
girders during fabrication. The Canadian Highway Bridge Design Code (CHBDC S6-06) limits
the number of debonded strands to a maximum of 25% of the total number of strands in the
girder. Design engineers have found the code clause to be somewhat unclear and have often
questioned whether the limits are applicable to girders which are pre-tensioned and posttensioned.
In Alberta, it has been typical practice for designers to limit the percentage of debonded strands
to between 25% and 40% of the total number of pre-tensioning strands in the girder and to
stagger the strand debonding locations. On a recent project, NU girders were fabricated with
over 50% debonded strands, all of which were debonded concurrently. This paper presents the
engineering rationale that was developed to support the acceptance of these girders.
