For lanes defined from frame elements, the moving load is applied directly to the frame elements that were used to define the lane. This true for zero-width lanes as well as nonzero-width lanes.

To obtain more realistic load distribution to all girders, you may need to define the lane from Layout line (this requires the [bridge modeler license]), specify lane width to match the width of the structure, and make sure that the group loaded by lane (on the lane definition form) contains all frame element representing the girders.

Eccentric load applied to lanes defined from frames

When an eccentric vertical load is applied to a lane defined from frame elements, SAP2000 will apply this eccentric load directly to the frame element that was used to defined the lane using the vertical load and torsional moment (to account for the eccentricity) as follows:

• The vertical load is applied at the centerline of the frame element at the location that corresponds to the intersection of the frame centerline and a line perpendicular to this centerline and passing through the location of the eccentric load.
• Torsional moment is calculated as a product of the vertical load magnitude and its transverse eccentricity from the centerline of the frame. This torsional load is applied at the same location as the vertical load described above.