Section-cut forces for moving-load analysis represent the actual forces which occur at any given section cut. For various configurations of live-load application, extreme resultant forces which occur within a section cut are not combined as this would overestimate section-cut forces. This concept is demonstrated in the attached model, where lanes and section cuts are defined as shown in Figure 1:
Figure 1 - Lane and section-cut definition
A vehicle of unit load is applied to the structure such that it travels along the lane, producing the moment diagram shown in Figure 2:
Figure 2 - Moment diagram
Since each girder is 10m long, maximum midspan moment under unit loading is calculated as 0.5kN (reaction) * 5m (length) = 2.5kN-m.
Two section cuts, one using groups and one using a quadrilateral cutting plane, are defined through each midspan location. As expected, the section-cut moments reported are also 2.5kN-m (Figure 3), indicating consistency between theoretical and software-generated results.
Figure 3 - Section-cut moments reported