It's the so-called "Angerschlucht bridge" aka "Angertal bridge". As far as I have seen, there is no dedicated Wikipedia page about it, but you can find some information on Wikipedia:
http://en.wikipedia.org/wiki/Tauern_Railway A photo showing the old and the new bridge is also available:
http://de.wikipedia.org/wiki/Datei:Tauernbahn-Angerschluchtbr%C..e.jpg