Elastic Section Modulus or Plastic Section Modulus?

[ghcaste]

Hello,

What is the difference between using Elastic Section Modulus (S) and Plastic Section Modulus (Z). I am desigining a base plate which happens to work if using Z, but it does not if using S. I am working usin Limit States Dedign (Canadian Code). Thanks for any input..

 

[SteelPE]

The elastic section modulus relates to when the extreme outer fiber of your section has reached yield. The plastic section modulus relates to when the full cross section has reached yield.

 

[ghcaste]

Thanks SteelPE,

That means that when using plastic section modulus, I am using the full capacity of a section; so if using elastic instead of plastic, am I being just conservative? or what other implications may have using one or the other?... Thanks again

 

[BAretired]

The Canadian Code recognizes LSD, Limit States Design (RLFD, Load and Resistance Factor Design in USA). The factored moment resistance, Mr = phi*Z*Fy for Class l and 2 sections. A base plate would be Class l.

The section modulus S would be used for determining stresses within the elastic range. It is also used in determining Mr for Class 3 sections (not applicable to a base plate).

Look at page 1-33, Article 13.5 in your CISC Handbook of Steel Construction.

BA