definitation of do (C1.7) and 0.8D for prestressed concrete members

[sanji02]

Hi,

the definition of do:

distance from the extreme compressive fibre of the concrete to the centroid of
the outermost layer of tensile reinforcement or tendons (not less than 0.8D for
prestressed concrete members)

Does anyone know where (and/or how) the 0.8D for prestressed concrete members come from?

Regards
sj

 

[rapt]

Initially ACI318.

It is also in Compression Field Theory in the Canadian Code/AASHTO/AS3600-2018 for RC and PT members.