The "core" of the cross section is used in various calculations.
Refer to "About shear core" in Chapter 22, "Defining Design Strips" for explanation of the core calculation.
Tendon ducts in this core are investigated.
Ducts are assumed to have the same heights as their widths and are assumed to be rectangular in shape. For all standard ducts, these assumptions give a conservative approximation of overlapping.
Ducts are assumed to be centered on the prestressing steel that they contain (this is not true in the real structure, but this assumption rarely has any impact on the calculation result).
Any horizontal line across the core is investigated to determine the maximum total width of duct across the shear area. Bonded duct widths and unbonded duct widths are multiplied by factors that differ for each code. For example, in BS 8110, 2/3 of bonded duct widths are considered, and full unbonded duct widths are considered. For ACI, the factors are zero, so the duct width is never excluded.
The web width is equal to the core width minus the maximum total width of duct across the shear area.
