does the Tappan Zee Bridge float?

Answer 1

The bridge is "floating" in the sense that the supporting caissons are not in direct contact with the bedrock (located about 300 feet below the bottom of the river water, under a pile of silt!).

However, the caissons are supported by steel encased concrete piles drive down to and into the bedrock. Therefore, the caissons are not truly "floating" ... and therefore neither is the bridge.

See the write-up and pictorial representations found at the link below.

Answer 2

According to the pic I saw of the bridge, no it is not floating. Check it out at: http://www.nycroads.com/crossings/tappan-zee/
or at: http://www.tzbsite.com/