Flange lateral bending stresses for design requests involving bridge object I-girders are evaluated only for models in which the bridge girders are modeled either by shell elements for both the webs and the flanges or by shell elements for webs and frame elements for the flanges; the latter is referred to as mixed modeling.

For static load cases and the mono symmetric I section, the lateral bending stress can be obtained using one of the following formulas:

(stress at edge) - (stress at web flange juncture)
[ (stress at left edge) - (stress at right edge) ] / 2

As illustrated in Figure 1, this correctly approach captures lateral bending stresses due to minor moment and due to warping. CSI Software creates a section cut containing only the top or bottom flange area objects, then omits flange axial force (which is due to the moment about the beam major axis) to calculate flange lateral bending.

Figure 1: I-Girder flange stresses due to major moment, minor moment and torsional (warping) moment

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