02-24-2009 07:20

Calculation of section properties for user-defined shapes


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03-28-2014 08:51

In the "SECTPROP.xls" spreadsheet workbook in the "Stress" worksheet, I added/expanded the comment boxes pertaining to the original general stress equation used to better clarify the equation's use and how the sign convention used in the worksheet relates to the original equation.
Also, in the "Points" worksheet where a plot of the cross section is created, I revised the procedure for obtaining/maintaining a more correct aspect ratio for the plot. Off of the calculation page and to the upper right, the user now inputs a value which is termed as "Axes Lengths Ratio"......the ratio of the actual on-screen measured lengths of the X and Y axes. This should keep the plot looking more to correct scale than has been in the past.
The current version of this workbook is now version 2.6.

05-01-2013 09:13

Due to technical difficulties, the author has been unable to post the following response to inquiries below:
"My uploaded, updated version 2.5 of this workbook addresses your earlier comment pertaining to the "bug" involving adding cylinder shapes in the "Shapes" worksheet.
Now, in regards to your other comment with your hypothetical case of an L8x4x1 unsymmetrical member with Mx = 200 ft.-kips (yikes!), what you are failing to account for is the member being unsymmetrical, thus, with rotated principal axes, X' and Y'. That does make a difference.
Please note that if you change the value of the property, Ixy = 0, thus assuming a symmetric shape, then the calculated stress would be -170.69 ksi, as you stated. Calculated by hand, f = Mx*(12)*(cy)/Ix = 200*(12)*(4.95)/69.6 = 170.69 ksi, matching what the spreadsheet gives you. "

04-30-2013 16:17

Regarding the 2013 update to Version 2.5, the author states:
It was brought to my attention that in the "Shapes" worksheet of the "SECTPROP.xls" spreadsheet workbook, if the user was adding multiple cylinders the program was inadvertently only referencing the values for the first cylinder that was input when determining the composite section properties. I have made the necessary cell referencing corrections pertaining to only the cylinders. The other shapes were fine.
While I was at it, I decided to expand the capability of the "Stress" worksheet in this workbook. Before, the worksheet only allowed the user to determine the combined stress at one point within the cross section at a time. I have expanded that now so that the worksheet can calculate and display the stress results for up to six (6) points at one time. I also added a cautionary note to remind the user to make sure that the points to be investigated are actually within the given cross section.

12-13-2012 08:25

I couldn't get an expected answer in the "Stress" tab for a simple scenario.
Using an L8x4x1 (unsymmetrical) with an Mx=200 k-ft, i expected a stress of 171 ksi at location x=-1.05, y=4.95. But the program gives -307.08 ksi.
Properties used: A=11, Ix=69.6, Iy=11.6, Ixy=-15.27.
Coordinates: x=-1.05, y=4.95
So I am suspecting there may be an error somewhere in the calculation for unsymmetric sections.
I don't know enough about the theory behind the formulas so I can't offer a solution.

12-13-2012 08:19

I noticed an error in the calculation of properties for cylinders in the "Shapes" tab. The As, Ixs and Iys values (hidden cells) only reference cylinder #1.