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

Chapter 8 - Bending Members

2006, 2007, 2008 T. Bartlett Quimby

Introduction


Flexure


Shear


Deflection


Misc. Limit States


Beam Design

Chapter Summary

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Section 8.5.2

Web Crippling

Last Revised: 06/06/2016

Figure 8.5.2.1
Web Crippling
 

Web crippling is actually local buckling that occurs when the web is slender (i.e. h/tw is large).  Figure 8.5.2.1 is a rough illustration of the behavior being considered.  The behavior is more restrained when the point load is applied away from the ends of the member, consequently there are separate equations for when a concentrated transverse load is locate near or away from the end of the member.

This limit state is to be checked at each location where a concentrated force is applied transverse to the axis of a member.

The Limit State

SCM specification J10.3 covers web crippling due to concentrated point loads applied to the flange.

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:

LRFD ASD
Ru < fRn Ra < Rn/W
Req'd Rn = Ru / f < Rn Req'd Rn = Ra  W < Rn
Ru / (fRn< 1.00 Ra / (Rn/W) < 1.00
f = 0.75 W = 2.00

[2010 Spec note:  The variable 'N' in the 2005 Specification has been replaced with 'lb' in the 2010 Specification.]

The values of Ru and Ra are the LRFD and ASD factored loads, respectively, applied to the beam. 

In this case Rn is the nominal web crippling strength of the member is computed using SCM equations J10-4 and J10-5.

The two equations are needed to account for the difference in available web material between the web at the end of the beam and the web away from the end of the beam.  The same principle was discussed in the section on web yielding.

Equation J10-4 (see SCM specification J10.3) applies when the applied force is not near the ends of the member.  It is a buckling equation and has numerous terms.

Equations J10-5 apply at the ends of the member.  The two equations are slightly different and depend on the ratio of bearing length to overall depth of the beam.

Sample Spreadsheet Calculation

The given spreadsheet example computes the reaction capacity, Rn, as controlled by web crippling for a typical W section. The input values are in the grey shaded cells and the results in the yellow highlighted cells.

Web Crippling      
SCM J10.3      
         
Section W12x65      
Steel: A992      
Fy 50 ksi    
N 5 in    
       
Tabulated Section Properties    
d 12.1 in    
tw 0.39 in     
tf 0.605 in    
       
  Mid End    
Rn 299.6 159.9 k <---- Answer

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