internal unbonded tendons are used widely in prestressing
concrete building structures. In the last decade, external
prestressing tendons have also found use in the rehabilitation
of structures, where they function primarily as unbonded
tendons. In addition to the conventional application
of unbonded tendons in post-tensioned construction, they
are used in precast concrete framing systems, particularly in
relation to forming con nections for precast structures in
sei smic zones.'-2
Flexural deformation of an unbonded prestressed member
subjected to load leads to an increase in the stress level in
the tendon. Fig. I shows a simply supported, unbonded pre-
PCI JOURNAL
stressed concrete beam subjected to a
concentrated load