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Section 8.5.2
Web Crippling
Last Revised: 06/06/2016
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Figure 8.5.2.1 |
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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 |
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.
SCM Equation J10-4 (see SCM J10.3) applies when the applied force is not near the ends of the member. It is a buckling equation and has numerous terms.
SCM Equations J10-5 apply at the ends of the member. The two equations are slightly different and which one to use depends 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 | ||
| lb | 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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