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The "Top slab cut distance" and "Bottom slab cut distance" are user-defined distances that specify what depth of the box girder will be considered as top or bottom slab for the purpose of design. The "Top slab  cut distance" is measured downwards from the top of deck and the "Bottom slab cut distance" is measured upwards from the bottom of the box girder - please see the figure below

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!Slab_cut_distance.png!

h1. Use in design

The slab cut distances are used in design as follows (refer to the bridge superstructure design manual for additional details):

* The equivalent slab thickness used for design is evaluated based on the slab area and slab  width, assuming a rectangular shape, as  t_slabarea =  A_slab/b_slab.
* The slab tributary area for each girder (web) is determined from the sectional polygon. For the top slab height-wise it includes everything above the top cut line. Width-wise it includes half distance between girders, for exterior girder the entire outside cantilever is included.

The values of ThSlabTop and ThSlabBot can be different for interior and exterior girders, because the exterior girder may include the entire cantilever slab (top slab) or no slab on the outside face of the web for bottom slab.

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