Section 27-567. Contributory floor areas

For purposes of computing live load
  reduction, contributory floor areas shall be determined as follows:
    (a)  For  the  design of one-way and two-way slabs: the product of the
  shorter span length and a width  equal  to  one-half  the  shorter  span
  length. Ribbed slabs shall be considered as though the slabs were solid.
    (b)  For  the design of slabs in flat plate or flat slab construction:
  one-half the area of the panel.
    (c) For the design of columns and  girders  or  trusses  framing  into
  columns:  the  loaded  area directly supported by the column, girder, or
  truss. For columns supporting more than one floor, the loaded area shall
  be the cumulative total area of all the floors that are supported.
    (d) For the design of joists and similar multiple members framing into
  girders or trusses, or minor framing around openings: twice  the  loaded
  area directly supported but not more than the area of the panel in which
  the framing occurs.