and was ignored in the force and moment calculation and monotonic loading and
deformation of the section.
The compressive force in each fiber layer was calculated as the product of the area
of the fiber layer and the average stress. The average stress was determined based on the
strain in the fiber layer and the stress-strain curves of concrete. The Hognestad parabola
was used to calculate the stress-strain curve of unconfined concrete. The modified
Hognestad was used to calculate the stress-strain curve of confined concrete. The
parameters of the modified Hognestad were determined based on the available data from
confined concrete cylinder tests.
.^r ~ ^ ....... ---------- ^
.y ------------- -- -------- a_. _--_ _._-
--- 0 ------ ---------- ------ 0 ----
Axis
Void
Figure 6-42. Spun cast cross-sectional fiber model
The tensile force was calculated as the product of the area of carbon reinforcement
and the stress in the carbon reinforcement which was determined based on the strain. The
stress in the carbon reinforcement was calculated based on an assumed elastic stress-
strain curve for the carbon reinforcement as reported by the manufacturer.