MDX Software - FAQ #28
What is the meaning of the table
heading 'Lateral Bending Moment (x girder ht)' in the system analysis output?
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Nonuniform torsion (warping torsion) is distributed along a curved girder.
The intensity of this distributed torque is M/R, where M is the longitudinal
moment, and R is the radius of curvature. This distributed torsion is
converted to a distributed force couple by dividing it by the depth of the
girder, producing a nonuniform line load in a horizontal plane on the side of
each flange. The accepted lateral bending moment at a brace in either flange
caused by this line load is 'qL**2/12,' where q is the intensity of the line
load at the brace, and L is the distance to an adjacent brace. Because the
depth of the girder may not be known at the time system analysis is processed,
the table has been 'nondimensionalized' with respect to girder depth d. That
is, since q = M/(Rd) and lateral bending moment (LBM) at a node is LBM =
qL**2/12 = M/(Rd)(L**2/12), then (LBM)(d) = (M/R)(L**2/12), producing values
tabulated in the table. Lateral bending in the flange at any node (brace) is
obtained by dividing the tabulated value by the girder depth.