The first step in Girder System Projects is defining the framing plan and basic slab dimensions. There are two distinct approaches to defining layout: (1) Parallel/Concentric layout, and (2) General layout.
Parallel/Concentric layout can be used when girder spacing does not vary along the bridge. Girder spacing can be different among the various girders. This approach involves geometry generation from a minimum amount of data: number of girders, girder spacing, span lengths of the rightmost girder (Girder 1), support skew angles measured at Girder 1, intermediate bracing locations along Girder 1 (and along other girders if bracing is not radial throughout the bridge), and horizontal radius of curvature along Girder 1. Skewed layouts require additional information to place bracing on radial lines that do not intersect Girder 1.
General layout must be used when girder spacing does vary along the bridge, such as in splayed and flared framing plans. This approach involves defining the framing plan by specifying global coordinates for nodes where bracing is attached to girders. This approach can be used for almost any framing plan, but is less convenient than the Parallel/Concentric approach.