Above picture is from Eurocode 3: design of steel connections. It gives geometrical requirements for a pin ended member. Looking at situation A, we have the minimum distance $c$ from the edge of the hole to the edge of the connection. I wonder where that term $\frac{d_0}{3}$ comes from?
Neglecting the safety factor $\gamma$ for simplicity, we should have the nominal stress on each side of the hole as: $$\sigma = \frac{F_{Ed}}{A} = \frac{F_{Ed}}{2ct}$$
At the yield limit, the stress equals the yield stress $f_y$:
$$f_y = \frac{F_{Ed}}{2ct}$$
Solving for $c$:
$$c = \frac{F_{Ed}}{2t f_y}$$
Now, there is no extra term $\frac{d_0}{3}$ here. Where does it come from in the Eurocode formula? My guess is that it could have something to do with stress concentrations, which we know to be around 3 times the nominal stress around a hole, but I don't really see how we would incorporate that into the equation, besides maybe multiplying the nominal stress by 3 before solving for $c$:
$$f_y = 3\frac{F_{Ed}}{2ct}$$
$$c = \frac{3F_{Ed}}{2t f_y}$$
But that is not the same result.