* 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.