Thank you for the response and feedback,
I repeated the simulation with double the time period of the impulsive force, and the results are the same. I'm summarizing my thoughts here for brevity:
The model has a high first fundamental mode ~ 700 Hz so it is less likely to have a strong response. Usually, I've seen models with low first natural modes of vibration (~ 10-20 Hz) generate a strong response to an impulsive load.
The pressure curve is actually a short spike and is being approximated as a sawtooth function for simplicity
Lowering or absence of damping should yield a stronger response for a conservative estimate, which is not resulting in any change in my case
Increasing or decreasing the time duration of the pressure impulse has no effect on the model