In SP-16, Design charts for combined axial compression and bending are given in the form of interaction diagrams in which curves for Pu/fckbD versus Mu/fckbD² are plotted for different values of p/fck, where p is the reinforcement percentage.
Charts for rectangular sections have been given for reinforcement equally distributed on two sides (charts 27 to 38) & for reinforcement equally distributed on four sides (charts 39 to 50).
In STAAD Pro, during design of a concrete column member using IS456 code, user can specify the face of the column for longitudinal bar arrangement using the RFACE parameter.
There are three options,
- RFACE 2 – reinforcement shall be placed along the 2 edges parallel to local Z axis
- RFACE 3 – reinforcement shall be placed along the 2 edges parallel to local Y axis
- RFACE 4 – reinforcement shall be placed on four sides
Now, let us under stand the local Y and Z axis of member.
In STAAD Pro Property window is being seen as below:
As you can see, YD is depth and ZD is width of member as per property window. Let us see the isometric view of member with local axis.
Red – Y axis
Green – Z axis.
The input syntax of property will be 1 PRIS YD 0.23 ZD 0.45
From the above image and syntax, we can see that Yd < Zd in this case. If you want to put reinforcement in two sides (longer sides), you shall have to provide along ZD in this case. Hence, you shall have to provide RFACE 2.
Hence, you can remember it this way,
If ZD > YD, then specify RFACE 2 parameter.
If YD > ZD, then specify RFACE 3 parameter.
Let us remember it with image,
 |
| RFACE 2 |
 |
| RFACE 3 |
RFACE needs to be provided to instruct the program to use more accurate interaction diagram and provide reinforcement as per actual condition.
To understand it better, you can watch this video.
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