Multi Shell Model for Majumdar-Papapetrau Spacetimes
  Exact solutions to static and non-static Einstein-Maxwell equations in the presence of extremely charged dust embedded on thin shells are constructed. Singularities of multi-black hole Majumdar-Papapetrou and Kastor-Trashen solutions are removed by placing the matter on thin shells. Double spherical thin shell solution is given as an illustration and the matter densitiies on the shells are derived. 
Metin Gurses and Burak Himmetoglu