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Second Moment of Area

This article explains the cross arm parameters Second Moment of Area vs Horizontal/Vertical which is found in the components library. The Second Moment of Area is a measure of the stiffness of a object due to its geometric shape.

The following diagrams show where the Neutral Axis axis is for the Second Moment of Area vs Horizontal and Second Moment of Area vs Vertical.

Example

The formula for the second moment of area for a rectangle around the centroid (neutral axis) is:

Consider a cross arm that is 100mm wind and 150mm deep as shown below.

The second moment of area for a vertical and horizontal force would be calculated as:

Note this example ignores the the impact of the kingbolt hole.

Note that these two values above match what Neara calculates using the button Derive assuming rectangular cross section as can be seen below.