I'm modeling/designing a 2-way transfer slab for a concrete podium building in RAM Concept and the program is adding one-way shear reinforcement around the columns. I was reviewing an audit of the cross section and noticed the following:
Why is the program adding shear reinforcement if the audit indicates they are unnecessary? Is there a setting I can check/update to avoid having the unnecessary shear stirrups added to the slab?
Thanks!
Just uploaded, please note that out workflow is through RAM SS but we have not been updating loads from RAM SS because we have custom load cases and load history calcs that get wiped out with bringing those in.
Thank you
Ground Floor or Second? Any strip in particular?
Let's consider Second floor, strip 2C. A plot of the shear density is useful to establish which sections require the shear reinforcement.
Here's the audit for the controlling section on the left.
Auditing 2C-3, section 1.html
If you are comparing Vu to Vc remember to incorporate phi (0.75) and recognize the requirement of 9.6.3.1 (* only for beams in ACI 318-14 *):
In this specific case, the phiVc limit is exceeded, so minimum shear reinforcement is required. At the next section it is OK and the next section is 1.45' away which is approximately "d", so I think you would be justified in ignoring this bar set. Adjusting the strip support width is another way to account for this, but since "d" is a moving target and since the sections are also critical for checking flexure, proceed with caution.
Seth,
Thank you this was helpful but it's brought up a couple more questions.
1. Why is the slab shear being designed with the Chapter 9 BEAMS code provisions? We would assume that 8.5.1.1 (c) governs for two-way slabs. Even table 9.6.3.1 you refernced provides exceptions for beams that behave more like slabs.
2. The bw used for the shear sections in the 2C audit seems to be the column strip width, but the shear load appears to be higher than we would expect for just that section. Does CONCEPT redistribute the shear for the design strip or is this just a function of the finite element design? Would modelling the design strip as "Full Width" instead of "Code Slab" alleviate this distribution? In either case, the shear is averaged over the cross section, but full-width design strips would seem to be more in-step with 8.5.3.1.1.
1. My error. I confess to still being more familiar with the older code layout. For two-ways slabs we are following the chapter 8 sections. In the case above the max shear demand was more than phi Vc.
2. The demand is a result of the finite element analysis. A full width strip would certainly give you a much larger capacity with only a bit larger demand.