* Perfect bond between the reinforcement and the concrete (strain compatibility)
* Monotonic loading and deformations of the section
* Ignore confining effect on concrete
The internal section forces of the cross-section are generated for a specified section
curvature and a specified axis location. The elastic centroid of the cross-section is
choose as an arbitrary reference centroid. The flexural moments of the section are
computed with reference to axes that pass through the reference centroid.
The contribution to the axial force and moment of the compression zone of the
concrete is determined by first meshing the geometry into trapezoids and then applying
numeric integration procedures. By numerically integrating the concrete stress surface
over each trapezoid in the meshed section the contributing force from each trapezoid is
found. The sum of all the trapezoid forces is the contribution of the concrete to the
internal axial force. The moment contributions are computed by multiplying the force
from each trapezoid with the distance between the reference centroid and the force.
The strain in the reinforcing bars is assumed to be uniform and is used in
conjunction with the reinforcement stress-strain diagram to compute the stress. The force
in the bar is the area of the bar times the stress taking into account concrete displaced by
the reinforcement bars. The sum of all bar forces is the contribution of the reinforcement
to the internal axial force. The moment contributions of the reinforcement are computed
in the same manner as for concrete using the distance from the reference centroid.
The total internal axial force is the summation of all the concrete and reinforcement
axial forces with their respective signs. The total moment of the section is the summation
of the moment contributions of concrete and reinforcement.