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- For each girder (web), the tributary slab area is determined from a section polygon that is constructed as follows:
- For top slab in the vertical direction, all concrete area above the Top Slab Cut Line is included.
- For bottom slab in the vertical direction, all concrete area below the Bottom Slab Cut Line is included.
- For interior girders in the horizontal direction, all concrete area between half distance to adjacent girders is included.
- For exterior girders, the entire outside cantilever is included.
- Once the tributary slab area, A slab , is determined, the equivalent slab thickness is evaluated, assuming a rectangular shape, based on slab area and width (as t slabarea = A slab / b slab).
Please refer to the Bridge Superstructure Design Manual for additional details.