722.214.171.124.1 Reentrant Space Filled
For wide-flange structural steel columns completely encased in concrete with all reentrant spaces filled [Figure 722.5.1(6)(c)], the thermal capacity of the concrete within the reentrant spaces shall be permitted to be added to the thermal capacity of the steel column, as follows:
bf = Flange width of the structural steel column (inches).
d = Depth of the structural steel column (inches).
As = Cross-sectional area of the steel column (square inches).