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Author Topic: Reporting of details for Crippling stress reports  (Read 9000 times)

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Reporting of details for Crippling stress reports
« on: February 15, 2011, 10:21:42 AM »
we found some error in the calculation of crippling allowable for I beam section.
Can you please verify our finding?
If yes, Is it a general error (also implemented in stiffened panels)?
If not, what are the reasons for the different calculation?

Details:
I-Beam
Height = 32 mm
Web, upper and lower flange thickness = 3 mm
Upper and lower flange widths = 90 mm

In the crippling stress reports, the b widths are reported as follows:
Flange Top          90 mm
Web                  26 mm
Flange Bottom     90 mm

The b width of the web is reported as 26 mm, however if the thickness of the flange is taken into account, it should be 29 mm ( = 26 + 3/2 + 3/2)

« Last Edit: February 15, 2011, 10:28:23 AM by Phil »

Phil

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Re: Reporting of details for Crippling stress reports
« Reply #1 on: February 15, 2011, 10:23:53 AM »
This discrepancy is really a reporting issue rather than a calculation issue.

There are two width values that are used in the software in the crippling calculation. The first b value is used to calculate the Fccn allowable crippling stress.

In the example shown, this value will be 29 mm rather than 26 mm and will feed into Eq 50.2 or 51.2 (depending on which crippling method you are using).

The second b value is used to calculate the areas when summing up forces. In other words, to calculate total force on an object, you multiple the stress times the width b and the thickness t. It would be inappropriate to use overlapping widths in this calculation because the total amount of force would be overstated.

This second value of b is what is reported in the tables of the stress report.

If you look at the b value for the upper and lower flanges you will see that they are for the entire flange width (90 mm) and not for the width that goes into the Fcc calculation (45 mm).

Thanks for pointing this out. The proper width used to calculate Fcc will be included in the stress reports in the next update.