February 19, 2018
Masonry Cover Flexibility in RISA-3D
In RISA-3D we now have the ability to:
- Define a cover other than the minimum from the ACI 530 code provisions
- Define a single reinforcing bar that is non-centered in a grouted masonry cell
From the Wall Design Rules in RISA-3D:
We can see here that a new option is available in the Bar Placement column called Non-Center that allows you to place a single non-centered bar in a cell.
The Cover then allows you to specify the distance from the exterior of the masonry block to the extreme fiber of the reinforcement. The default cover value is defined as Min. The Min input will use whichever governs between these two sections of the specification (ACI 530-13):
- Section 126.96.36.199 states a minimum distance between the inside of the face shell and the reinforcement is required. RISA is conservative and always assumes this to be 1/2″. Thus, the cover calculated in this fashion = t_faceshell + 1/2″
- Section 6.1.4 requires a cover dimension = 1-1/2″ or 2″ depending on bar size and whether the masonry is exposed to weather. In the program this is always assumed to be 1-1/2″.
Thus, the Min term will create a cover equal to the maximum of t_faceshell + 1/2″ OR 1-1/2″.
For any other cover you wish to impose simply overwrite the Min value with your value. If you’re using the Non-Center option then the cover will always be from the +z local axis face of the wall.
For example, let’s assume the wall shown below is using the “Non-Centered” reinforcement and the cover is set to 2.5″. The image below shows exactly where this bar is then located in the wall (d = 7.625″ – 2.5″ – 3/8″ = 4.75″).
In this case the actual “d” used in design will depend on the governing direction of loading. If load is applied in both out-of-plane directions to the wall then it is possible that a lower level of loading can produce a higher code check because the “d” is smaller in one direction than the other.