Applies To
	Product(s):	STAAD Foundation Advanced
	Version(s):	ALL
	Environment:	ALL
	Area:	General
	Subarea:	Rigid Foundation
	Original Author:	Sye Chakraborty Bentley Technical Support Group

In an isolated footing design, STAAD Foundation Advanced reports the minimum reinforcement ratio to be less than the values specified by ACI 318 code. For example I am using the ACI 318 code and for 60 ksi steel, I would expect a minimum ratio of 0.0018 as per clause 7.12.2.1 but STAAD Foundation Advanced shows the min reinforcement ratio to be 0.0016. Why is that ?

 

STAAD Foundation Advanced does check the minimum reinforcement as per the ACI clause 7.12.2.1 but depending on a global setting, it can provide the minimum reinforcement such that

 

1. The minimum reinforcement requirement is satisfied considering both top and bottom reinforcements or in other words the summation of the reinforcement required at the top and bottom should equal the minimum reinforcement required.

2. The minimum reinforcement requirement is satisfied for each face individually in which case, at each face the min reinforcement ratio would be 0.0018.

    

If you go to Global Settings > Rigid foundation Settings > check the box which reads “Check Minimum Reinforcement based on top and bottom combined”, the software calculates the min reinforcement as per the point 1 above. So if there is a certain amount of reinforcement already provided at the top face, it would provide the remaining amount of steel ( for satisfying the minimum reinforcement requirement ) at the bottom face. In such cases you may see the min reinforcement ratio reported to be lesser than 0.0018 as this is for that particular face only and not for the entire cross section.

 

If the box is unchecked, the software calculates the min reinforcement as per the point 2 above. If you design with this setting, you would see 0.0018 being reported as minimum reinforcement required at a single face.