Values of f2,, and a can be calculated
by the formulas in ACI 318-71. Eq. (1)
is the same formula that appears in
the Commentary to ACI 318-71 with
cp (capacity reduction factor) equal to
one. When the temperature of the steel
is increased to some temperature 0,
values of f,8 and a must be reduced to
reflect the new temperature. M
the moment capacity with the steel at
temperature 0, and is termed the "retained" or "residual" moment capacity.
Theoretically, during a fire test, a
structural end point will occur when
the residual moment capacity is reduced to that of the applied moment.