Tyra's Fire bomb is unaffected by Heaven or Blast shields. Be sure to avoid it at all costs unless absolutely necessary; Some healers such as Ying or Mal'Damba can prolong a frontlines' life in unavoidable situations.
As a frontline, Viktor's Barrage will be blocked by your shield if the center of the blast is outside your shield. The missiles are just a visual effect, and the explosions actually spawn at ground level.
Viktor's Barrage actually spawns explosions on the ground instead of dropping them from above. Moving backwards while he is locked on to you will make them hit your shield if you get the center of the blast off you and in front of your shield.