Combinations and strength reduction factor in ACI

The article explain how to create the combinations according to ACI and how is reduced the strength of concrete and reinforcement bars.

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.