Punching shear capacity

[Anonymous]

I'm a student and I'm not really experienced using Robot Structural. During doing a simple small project I realized something that doesn't make sense to me about punching shear. In the same project I tried to use 30x30 cm columns and the slab failed by punching shear, but using 25x25 cm it have the enough capacity for the structural requirements. Why this happens? Isn't having a column with a larger area supposed to increase punching shear capacity? 

I leave attached the results with both sections.

I will appreciate your help and guideline!

[Krzysztof_Wasik · Accepted solution]

Hi @Anonymous 

For column 25x25 program was able to define reinforcement for punching. For column 30x30 critical perimeter is smaller (probably due to column position in edge/corner region) and program cannot define required punching reinforcement. 

[Anonymous]

I understand. Thanks a lot!