RAM Concept rebar mysteries

[D.N.F.]

Has anyone noticed shear rebar determined by RAM Concept can vary depending on whether the longitudinal rebar is Program or User defined? On a recent podium slab project, the program determined that 6 #7 bottom bars were needed for a particular beam and that the stirrups at the right end needed to be #5 (2-leg) @ 4.55 inches (10 spaces). When the 6 #7 bottom bars were changed to User defined with no other changes to the length or location, Concept then determined that the stirrups at the right end needed to be #5 (2-leg) @ 7.98 inches (6 spaces). In both cases Concept showed that the shear at the right end of the beam is 184 kips. Manual calculations showed that the 7.98 inch spacing was correct. The attached file shows screen pictures of this odd behavior. Why Concept showed the 4.55 inch spacing when the program designed the bottom bars is a mystery.

Concept has also on occasion shown another odd behavior. After changing longitudinal rebar from Program to User defined, Concept sometimes then shows that more longitudinal rebar is needed. After deleting the rebar that had been changed to User defined and letting Concept once again design the rebar, it again shows the original lesser amount is required.

This behavior is not confidence building.

 

[SethGuthrie]

If you are not using the latest version 8.2, updating is a good idea.
If you want to send me your model I can also check it in the latest version.
Sometimes when you freeze one set of rebar (top or bottom) it will impact the rebar designed on the opposite face, and that might affect the final d value used thus impacting the shear bar spacing. See also:

https://communities.bentley.com/products/ram-staad/f/ram-staad-forum/104901/rc-slabs-in-ram-concept