Hello Elson
According to a brief comment by Jeff Wilson in his book Bridges, Trestles & Tunnels, Kalmbach Publishing, 2005, "Trestles with ballasted decks have floors with the track (laid on standard ties) resting on top of the ballast on the deck."
For plate girder bridges, photos on page 33 also suggest standard tie spacing on the ballasted deck.
Like most everything else in the prototype world, however, it's entirely possible different railroads used different practices.
Warmest regards
Bill Rice-johnston
