Example

Determine the nominal moment for lateral-torsional buckling strength for the I-beam used in Example 6.2. Assume that the beam is braced laterally at both ends and midspan. Use Fy = 50 ksi.

Solution

Calculation of sectional properties

Based on the dimensions given in Example 6.2 (Figure 6.19 and Figure 6.20), the moment of inertia, Ix, and the section modulus, Sf, of the full-section can be computed as shown in the following table:

calculate Fe:

Element

Distance from mid-depth, y (in.)

Flanges Corners Webs

Total

4(1.6775)(0.135) = 0.9059 4(0.05407) = 0.2163 2(7.355)(0.135) = 1.9859

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