Our client is really questioning the design of our purlins and want to make sure I am applying a section of the code correctly as I can not utilize the R-value method that pre-engineered metal building suppliers utilize in their designs.
I have calculated the z-purlin capacity connected to a standing seam roof system for Lateral torsional buckling (C3.1.2.1) and Distortional buckling (C3.1.4) based on AISI 2012 which is applicable to our current adopted code. I am using the commentary to get the distortional buckling stress, Fd, but have questions on the difference between Sf (elastic section modulus at extreme fiber in first yielding) and Sfy (elastic section modulus at at extreme compression fiber) in section C3.1.4. I used the effective section modulus of the top flange in positive moment for both these values as presented in the properties tables of the members I am using. Is this the correct approach?
I have calculated the z-purlin capacity connected to a standing seam roof system for Lateral torsional buckling (C3.1.2.1) and Distortional buckling (C3.1.4) based on AISI 2012 which is applicable to our current adopted code. I am using the commentary to get the distortional buckling stress, Fd, but have questions on the difference between Sf (elastic section modulus at extreme fiber in first yielding) and Sfy (elastic section modulus at at extreme compression fiber) in section C3.1.4. I used the effective section modulus of the top flange in positive moment for both these values as presented in the properties tables of the members I am using. Is this the correct approach?