K. CHO ET AL. 855
strain of the core wire. At the exception of the zones in
contact with the helical wires, the stress of the core wire
appeared to be nearly constant over the cross section and,
except the extremities, the stress of the core wire re-
mained also constant in the longitudinal direction. These
observations made it possible to presume that the mean
stress of the core wire could be directly obtained from
the strain measured at the mid-length center of the core
wire. On the other hand, since the stress varied inside the
section of the helical wire, the corresponding mean stress
was calculated indirectly. In addition, the relation be-
tween the mean stresses of the core and helical wires was
formulated using the helical angle. Based upon this rela-
tion, a formula computing the prestress of the strand di-
rectly from the strain measured on the core wire was
suggested. The proposed formula in combination with
the recently developed method measuring the strain of
the core wire can be exploited to determine the prestress
of the strand.
6. Acknowledgements
This research was supported by a grant from a Strategic
Research Project (Development of Smart Prestressing
and Monitoring Technologies for Prestressed Concrete
Bridges) funded by the Korea Institute of Construction
Technology.
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