The section properties are reported with respect to the section local axes (2-3), not the Section Designer X and Y axes. Furthermore the section properties are reported assuming that the entire section is transformed into an equivalent area of the specified base material. In other words, each infinitesimal area of the section, dA, is multiplied by the ratio Eshape/Ebase when computing the section properties where Eshape and Ebase are defined below. Using this transformation the following relationship holds true.
where,
Asection = Area reported for the section, length2.
Ashape = Area of a geometric shape (not reinforcing shape) included in the section, length2.
Ebase = Modulus of elasticity of the base material, force/length2.
Eshape = Modulus of elasticity of the material specified for the shape, force/length2.
n = Number of geometric shapes included in the section, unitless.
Important note: The reinforcing steel is not considered when calculating the section properties. This includes the reinforcing steel defined as a reinforcing shape and the reinforcing steel that is associated with a geometric shape. The section properties are based on the gross area of all geometric shapes transformed to an equivalent area of the base material.
The following section properties are reported:
A: Area of the section, length2.
J: Torsional constant, length4.
I33: Moment of inertia about the 3-axis, length4.
I22: Moment of inertia about the 2-axis, length4.
I23: Moment of inertia, length4. The figure below illustrates the derivation of I23, I22, and I33.
The I23 moment of inertia is equal to zero when the local 2 and 3 axes are the principal axes of the section. If the local 2 and 3 axes are not the principal axes of the section then I23 is nonzero.
As2: Shear area for shear parallel to the 2-axis, length2.
As3: Shear area for shear parallel to the 3-axis, length2.
S33(+face): Section modulus about the 3-axis at extreme fiber of the section in the positive 2-axis direction, length3.
S22(+face): Section modulus about the 2-axis at extreme fiber of the section in the positive 3-axis direction, length3.
S33(-face): Section modulus about the 3-axis at extreme fiber of the section in the negative 2-axis direction, length3.
S22(-face): Section modulus about the 2-axis at extreme fiber of the section in the negative 3-axis direction, length3.
r33: Radius of gyration about the 3-axis, length.
r22: Radius of gyration about the 2-axis, length.
Xcg: The Section Designer X-axis coordinate of the center of gravity of the section, length.
Ycg: The Section Designer Y-axis coordinate of the center of gravity of the section, length.