How to Calculate for Steel I Beams

A beam's dimensions determine its strength.
••• construction worker, image by Greg Pickens from Fotolia.com

Engineers use a structure's area moment of inertia to describe how well it resists load stresses. A beam with a higher area moment of inertia is less likely to bend or deflect when a load applies a force to it. Calculus determines this second moment of inertia for irregularly shaped beams. Rectangular beams, however, offer a simple formula for determining their moments of inertia. Calculate an I-beam's second moment of inertia by dividing it into sections and calculating each one's inertia.

    Raise the length of either of the I-beam's flanges to the power of three. If, for instance, each of the flanges are 6 inches long: 6 ^ 3 = 216.

    Multiply this answer by each flange's width. If each flange is 0.75 inches wide: 216 x 0.75 = 162.

    Multiply this answer by 2 to account for the two flanges: 162 x 2 = 324.

    Raise the distance between the flanges, which is the length of the webbing, to the power of 3. If, for instance, this distance equals 8 inches: 8 ^ 3 = 512.

    Multiply this answer by the width of the webbing. If the webbing is 0.75 inches wide: 512 x 0.75 = 384.

    Add the answers to Steps 3 and 5: 324 + 384 = 708.

    Divide this answer by 12: 708 / 12 = 59. The result is the I-beam's area moment of inertia, measured in inches raised to the power of 4.

Related Articles

How to Size H-Beams
How to Calculate Weight Per Linear Foot
How to Calculate the Length of Cable on a Drum
How to Solve a Hexagon
How to Calculate the Weight of Angle Iron
How to Find the Area & Width of a Rectangle
How to Find Dimensions in Geometric Shapes
How to Calculate Rebar Lengths
How to Find the Long Side Dimension on a Right Triangle
How to Calculate the Lineal Footage of a Circle
How to Size Gravity Drainage Piping
How to Calculate an Area in Square Meters
How to Calculate Photons Per Second
How to Calculate Triangle Dimensions
How to Convert RPM to MPH With a Calculator
How to Convert Square Dimensions to Round
How to Calculate Square Feet in a Triangle
How to Calculate a 3D Perimeter
How to Calculate Volume of a Rectangular Prism
How to Calculate Ramp Length

Dont Go!

We Have More Great Sciencing Articles!