# To Which distance Punching Shear Reinforcement is placed in Mat Foundation?

As I know, a thinner mat may be possible by providing a nominal amount of vertical reinforcement as compared to a mat without vertical reinforcement, the vertical reinforcement is used to resist punching shear at d/2 from columns or shear walls at foundation level.

Now my question is to what distance (or offset) from the column to stop placing these vertical reinforcement is it at a distance d/2 ?

Please if possible provide reference in ACI Code. What i need is the critical section outside slab shear reinforcement from which distance from the column ?

You need to check at $d/2$ from the column face to determine if shear reinforcement is required. If it is then you need to continue to check perimeters at a distance of $\alpha d$ from the column face until you find that (in SI units) $$\frac{\nu_u}{\phi} \leq \frac{0.17\lambda\sqrt{{f'}_c}}{2}$$
Then the outermost perimeter of shear reinforcement must be at least $\alpha d - \frac{d}{2}$ from the column face.
$\nu_u$ is maximum shear stress due to factored forces. $\phi$ is the strength reduction factor = 0.75. ${f'}_c$ is the specified concrete compressive strength. $\lambda$ is the modification factor for the reduced mechanical properties of lightweight concrete (=1 for normal weight concrete). $d$ is the effective depth of slab.