A Beginner's Guide to the Steel Construction Manual, 13^th ed. (old)

Chapter 8 - Bending Members

© 2006, 2007, 2008 T. Bartlett Quimby

Section 8.2.3

Flexural Yielding Limit State

Last Revised: 06/16/2011

As described in the section on flexural limit state behavior, the flexural yielding limit state represents that absolute maximum nominal moment that a section can support.  At this condition the section is fully yielded.  The limit state for strong axis bending in I-shaped member is found in SCM F2.1 and for weak axis bending in SCM F6.  Other situations are covered in other sections of SCM Chapter F and are similar to those presented here.

The Limit State

The basic limit state follows the standard form.  The statement of the limit states and the associated reduction factor and factor of safety are given here:

The values of M_u and M_a are the LRFD and ASD factored loads, respectively, applied to the flexural member. 

In this case M_n is the nominal flexural yielding strength of the member.  For doubly symmetric compact I-shaped members and channels bent about their major axis:

M_nx = M_px= F_yZ_x for strong axis bending (SCM equation F2-1)

M_ny = M_py = min(F_yZ_y, 1.6F_yS_y) for weak axis bending (SCM equation F6-1)

Where:

• M_p is the plastic flexural strength of the member.
• F_y is the material yield stress.
• Z is the plastic section modulus for the axis of bending being considered.

The following spreadsheet example computes the flexural capacity, about each principle axis, for a typical W section.  The input values are in the grey shaded cells and the results in the yellow highlighted cells.

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