Franconia/Springfield station will become Yellow Line trains & go from the Pentagon Station across the Potomac to L'Enfant Plaza and continue to Mt. Vernon Square.  There will be special trains from National Airport Station to Arlington Cemetery, and shuttle bus service between the Pentagon & Rosslyn.  In the city, all stations normally served by the Blue Line will be served by Silver line trains all the way to Largo.  The Smithsonian Station on the Mall will be closed because it is inside the security perimeter; it will re-open after the concert ends.
With a good weather forecast, free holiday parking at all Metro parking facilities, and all the big name stars involved, a crowd of at least 800,000 is expected.  My advice is, unless you are going to the concert, stay the H out of the city Tuesday!