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MARC1-2013 Module Z2/A and B stiffness coefficients
Ralph Aronberg of Aronberg and Associates pointed out an error in MARC1-Z2. I had simply calculated the average crush depth by dividing the summation of all crush depth measurements (2,4 or 6)by the total the number of crush measurements. While that is correct for two crush depth measurements, it may not be correct for 4 or 6 measurements. The average crush depth should be calculated by dividing the total crush area by the total crush width. In other words, the actual crush area (say a trapezoid) must be equal to the average crush depth multiplied by the total crush width. This change has been made and the latest MARC1 - 205 can now be downloaded from the website.
The average crush depth is used to calculate the b1 slope required foe the A and B-stiffness coefficients. See Equs. (21-28) and (21-29) in the 7th edition.