Analysis of Bolts: Modified Visual Basic Code for Calculating Bolt Coefficient Using a Method Developed by Donald Brandt

Written by Redeemer
Posted Monday, March 14, 2011 at 4:11:00 AM

Another blog post for Structural Engineers and Designers…

When I wrote and posted the VBA (Visual Basic for Application) Code for the analysis of eccentrically loaded bolt group in my blogpost, “Eccentrically Loaded Bolt Group: Analysis and Design using 'INSTANTANEOUS CENTER of ROTATION METHOD' with VBA for Excel Implementation”, I was aware of the difference between the values returned by the program and that of the table of C coefficients provided by AISC Steel Construction Manual. I never believed, however, that the values returned by the program are wrong. How could it be when the VBA code is based on the work by Crawford & Kulak as presented in AISC Steel Construction Manual 13th Edition, pages 7-6 to 7-8? Despite the differences, though, I still decided to post the VBA Code.

Not long afterwards, engineers who happened to follow my blog shared and expressed the same observations and 'demanded' an explanation. Here are some of their comments:

Blog comment from Josh Gionfriddo, EIT, Structural Engineer, Structures Workshop, Inc. on November 19, 2010:

Thanks for this great code. One thing though... The values in the AISC manual seem to hover around 98% of the values I get from your code. Any Idea why the differences?
Comment from Gregory Vidgop via AISC SteelTOOLS on October 11, 2010:

Hello Redem,

Thank you so much for your effort in developing the very nice and useful program as "SteelPro". Just would like to ask you a simple question: why is the C coefficient for the bolt group analysis slightly different from the book value and C' coefficient is exactly right?

Please let me know when your program will be finally issued or any revisions are planned in the future.

Thank you again, Gregory
Blog comment from Steven Vicha, P.E., Jacobs Engineering Group, Inc. on February 9, 2011:

Great code, but I have a couple of questions. In the code line "Rn = 74 * (1 - Exp(-10 * 0.34)) ^ 0.55" what is the 74? Also the answers are a little off from the tables, any idea why?

I need to study it some more.