60 Hz seems like a very high resonant frequency for a concrete pile cap. Have you verified all your inputs into DYNA? You would need a very low mass for this to be possible.
EDIT: Just did a quick check because I am sick and bored. Definitely need to add thickness, if you can't go up, go down...
The commentary in ACI 318-19 R.22.7.6 Torsional strength, states that the nominal shear strength Vc provided by the concrete is assumed to be unchanged by the presence of torsion. Seeing as your shear load than Vc, I would think you would be ok to design the main reinforcement with interaction...
