Calculating the Elastic Section Modulus, Sx, and Plastic Section Modulus, Zx, for a Plate Girder Bent About its Strong Axis

June 8, 2017 Abdul Siraj, P.E.

In this post, I will discuss the first example in our steel design course covering the analysis and design of beam members. The goal of this steel design example is to calculate the elastic section modulus, Sx, and plastic section modulus, Zx, for a plate girder bent about its strong axis. We are using the 13th edition of the AISC Steel Construction Manual.


The problem statement states,


For the plate girder shown below, calculate the:


  1. Elastic section modulus S and the yield moment My
  2. Plastic section modulus Z and the plastic moment Mp


Bending is about the strong axis

Material: A572 Grade 50