Inertia of I Beam: Calculating Based on Dimensions W360 x 44

[Precursor]

I need to find the inertia of an I beam given its dimensions W360 X 44.

I know that the formula is I = \frac{bh^{3}}{12}, but what do I plug in for b and h? I believe that I have to cut the I beam into 3 sections, the two flanges and the web. And 44 must be the width of the flange and web, but I don't know what 360 means.

 

[Precursor]

All I want to know is what does W360 X 44 mean?

 

[dav2008]

See Page 29: http://www.nucoryamato.com/StaticData/catalog.pdf?currdate=7/7/2009+6:24:14+PM (PDF)

This is a metric beam. The W designates the beam as a wide beam; the 360 refers to the nominal depth of the beam in mm, and the 44 refers to the mass/length of the beam. You can use that .pdf file to find out all of the geometric parameters of the beam, and it also provides you with a moment of inertia to which you can compare your answer.

Also you're right that you have to consider the flanges and the web, but make sure to use the parallel axis theorem when considering the different sections.

The formula you listed is strictly valid for a rectangular cross-section about the horizontal axis so make sure you understand what b and h refer to (See: http://en.wikipedia.org/wiki/Second_moment_of_area#Rectangular_cross_section )

The wikipedia page also has a walk-through of calculating the moment of inertia in case you have difficulties.