How does Floor Pro calculate Mcr (cracking moment)?
The default values that Floor Pro uses in determining the cracking moment are:
Beams & One-Way Slabs: S*7.5sqrt(f’c)
Two-Way Slabs: S*6sqrt(f’c)
Note that the user-defined input for allowable tensile stress (Total Service condition) is used in determining Mcr in ADAPT-PT. ADAPT-RC uses S*7.5sqrt(f’c) for beams and slabs.
In calculating cracked deflections for two-way slabs in Floor Pro RC, Ieff will be based on the default value shown above. For the program to calculate Mcr based on 7.5*sqrt(f’c) in lieu of 6*sqrt(f’c) the user can open in Floor Pro PT, save the model and then re-open in Floor Pro RC.
Note: For post-tensioned slab designs carried out in ADAPT-PT or Floor Pro, Mcr also includes the effects of pre-compression such that:
Mcr = S*(P/A + fr); where fr is based on criteria listed above