ACI Definition [1]

ACI 318-05 defines a drop panel as a "projection below the slab at least one quarter of the slab thickness beyond the drop."

Criterion [1]:

  • A drop panel must have a minimum thickness of at least that provided in the table here.
  • ACI 13.2.5 mentions that "when used to reduce the amount of negative reinforcement over a column or minimum required slab thickness, a drop panel shall project below the slab at least one-quarter of the slab thickness beyond the drop and extend in each direction from the centerline of support a distance not less than one-sixth the span length measured from center-to-center of supports in that direction."
    • To shorten this statement, if you're using a drop panel to reduce the amount of negative enforcement necessary you must: project the panel 1/4 of the slab thickness and extend the panel at least 1/6 the distance between supports.
  • ACI 13.3.7 mentions that "in computing the required slab reinforcement, the thickness of the drop panel below the slab shall not be assumed to be greater than one-quarter the distance from the edge of drop panel to the face of column or column capital."


To be inserted...


  1. American Concrete Institute, "Building Code Requirements for Structural Concrete (ACI 318-05) and Commentary (ACI 318R-05)", 2005



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