9.3.2 Strength Reduction Factors in ACI Code

9.3.2 Strength Reduction Factors

To be conservative, ACI code gives us a reduction factors to use it when we are designing concrete members. This reduction factors reduce the capacity of the member which make our design be safer. In section 9.3.2 we have two types of members; Tension-controlled sections and compression-controlled sections. If we have a tension-controlled sections (which most likely in beams) we will reduce the capacity of this section by 10%, so we will multiply the capacity by 0.90. And if we have a compression-controlled member (which is columns most likely) we will reduce the capacity by 30% if we are using spiral reinforcement or 35% if we are using other reinforcement. So we will multiply the compression-controlled capacity by 0.70 or 0.65 respectively.

If we have a member which is placed in Transition area the reduction factor will be taken like this:

Let’s discuss why the reduction factor in the tension-controlled members is less than the compression-controlled member?