VBG Explains Second Moment of Area

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The second moment of area is a measure of the ability of a structure to resist bending/deformation, and is denoted with I and units expressed as cm4, mm4 or m4. The higher the value of I, the more rigid the structure.

Since the requirements for underrun protection are based on a specific maximum deflection, truck frames must correspond to the rigidity levels that components are designed and tested for at VBG.

Simply put, small frames are weaker than large frames, but because the boundary can be difficult to determine, you need to be able to understand and calculate the value for your own structures. Geometry data can usually be downloaded from automakers’ bodybuilder instructions.

What is the Second Moment of Area and How is it calculated?

The calculation bases for beam bending are shown below, where I is an important element in the formula for deflection.


What is the requirement?

I = 5,700 cm4 is a minimum requirement and means that the frame on the truck must equal or exceed this value in order for a potential deflection to remain within certified levels. Owing to the new UNECE R58 Revision 3 regulations, we need to develop products with greater resistance to bending/deformation than before.

If you are interested in knowing more about what the new regulations mean, you can read our summary of regulations UNECE R58 revision 3.

Download summary of new R58 regulation

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