The correct answer is $\boxed{\text{A. }75 t^2/h}$.
The shear force at the connection of intermediate vertical stiffeners to the web is calculated as follows:
$V = 0.75 t^2/h$
where:
- $t$ is the web thickness in mm
- $h$ is the outstand of stiffener in mm
This equation is based on the following assumptions:
- The stiffener is perfectly welded to the web.
- The stiffener is not subjected to any external loads.
- The web is not subjected to any bending moments.
If any of these assumptions are not met, the shear force at the connection of intermediate vertical stiffeners to the web may need to be increased.
Option B is incorrect because it does not account for the outstand of the stiffener.
Option C is incorrect because it does not account for the web thickness.
Option D is incorrect because it is too high.