I'm wondering how to best go about analyzing this chord progression from the Billy Joel classic, "Vienna".
The song is in Bb-Major.
The first chord is an augmented I chord (I+), which seems strange. Maybe the #5^ is meant to create more brightness, or maybe it's borrowed from the relative minor's leading tone.
The second chord appears to be a German augmented sixth chord of scale degree 6, though it doesn't resolve the way this chord would.
The third chord is a D# fully diminished seventh chord in second inversion, though I don't know where this chord comes from.
Next is the Eb-major chord in second inversion.
Finally, there appears to be a C half diminished seventh chord in second inversion, then the dominant F7 chord, and finally the tonic Bb chord.
I'm trying to figure out how to explain all the strange chords and determine ways they can be analyzed. Any insights would be much appreciated!