Combinations, according to ACI
The combinations are created in a similar way for every design code. ACI has several specific combination rules that differ from Eurocode, for example:
ULS combinations: 1,40*Permanent load
1,20*Permanent load + 1,60*Variable load
SLS combinations are defined separately for Deflections and Crack width.
Strength reduction factor
According to the code ACI you should consider a Strength reduction factor based on the type of structure you are about to analyze. In IDEA StatiCa Detail, you have a Material factor, which reduces the characteristic strength of concrete and reinforcement. While the Strength reduction factor is considered as a multiplier (numerator) of the material strength, the Material factor is used as a divisor (denominator); because of that, the Material factor is γ=1/Ф.