The slab thickness is sufficient as I see, and shear r/f is not needed for slabs usually. Reinforcement net is top and bottom so, it’s also sufficient for a test run. Why these errors appear then?
Project file
Concrete 1.rf6 (7.3 MB)
Hi BigBoss,
Shear Reinforcement Settings in Concrete Design
The messages you're seeing are related to the design code requirements.
To clarify this further:
In the Concrete Design settings for members, you can define whether shear reinforcement should be determined—and if so, which type.
This setting plays a key role in complying with structural safety checks. 
You can find the relevant option here in the online manual:
Concrete Design Manual – Shear Reinforcement Settings
Best regards
Stefan Hoffmann
But usually for the slabs, shear r/f is not required. The reinforcement net provided is also more than the usual r/f and slab thickness also above average. Still shear errors occur why?
You’re providing such broad answers. Almost feel like I just clicked a search button and found some vague documentation.
Hi BigBoss,
Follow-up on Shear Reinforcement Checks
Hi and thanks for your follow-up question! 
In general, you can control whether the structural detailing requirements for shear reinforcement are checked, even if no shear reinforcement is required based on the calculations.
Customization Options
If you do not want these detailing checks to be performed in such cases, you can simply disable this option in the global settings.
Best regards,
Stefan Hoffmann
May be I’m not getting what you suggested me to do properly. As I understand from that screenshot, you’re just asking the software to “Do not check all reinforcements”. Then why we need a software if we do not check anything?
Does the software even have something more specific like “Do not check shear reinforcement”? So we check all other reinforcement and specifically disable shear checks?
I don’t see your suggestion as a solution, that’s just running away from the problem isn’t it?
I feel like software is not capable of disabling only the shear reinforcement, or software is incorrectly calculating reinforcement checks, as I have provided more than enough thickness for the slab, there can’t be any shear failures and shear reinforcements are not required for the slab of that size.
Hi BigBoss,
Tip: Controlling Shear Reinforcement in Design
You can control whether shear reinforcement should be avoided if the longitudinal reinforcement is sufficient.
However, if the longitudinal reinforcement is not sufficient—often the case near areas prone to punching shear—you may receive a high utilization ratio, as shown in your screenshot. 
What You Can Do:
-
Refine the FE mesh in the critical area
-
Check for punching shear at that location
This often helps improve the accuracy of the results and can reduce unrealistic stress concentrations.
Want to learn more?
Check out our webinar on the relevant add-on here:
Dlubal Webinar – Punching Shear Check
Best regards,
Stefan Hoffmann