Mike, when pouring the concrete for our clubroom/double obs, there is a strip of styrofoam between the clubroom floor and the obs floors.
The concrete is one long strip 14 metres long with the clubroom sitting on the centre 6m.
The 4m each out end is for the obs.
This way the obs floors, even though joined, are actually isolated by 10mm of styrofoam.
People can jump around in the clubroom, but not affect the obs at either end.
Point of the story: Yes, isolate the pier
