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Question:

How do I calculate the moment of inertia of an I-beam?

I know it could be broken down into rectangles and the formula (1/12)bh^3 could be used but.what values do i put in for h and b respectively when it is rotated about the both the x-axis and y-axis? I can't seem to find a website for this information.

Answer:

Two ways to determine moment of inertia for a structural shape: 1calculate individual component inertias and sum them using parallel axis theorem 2look up the value for the section in a steel or aluminum structural shape handbook If the section is rotated, find the inertia in a coordinate system aligned with the I-beam (find Ixx, Iyy, Iyy) and populate a 2x2 matrix with these valuesThen, develop the transformation matrix for the rotation that you need to perform to get the inertias in the original coordinate system.

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