public void SetMapFrame( 
   MapFrame mapFrame
)

{
  //Update a map surround.
  //Note: Must be on QueuedTask.Run
  // Reference and load the layout associated with the layout item

  // Reference a scale bar element by name
  MapSurround scaleBar = layout.FindElement("MyScaleBar") as MapSurround;

  // Reference a map frame element by name
  MapFrame mf = layout.FindElement("MyMapFrame") as MapFrame;

  if ((scaleBar != null) && (mf != null))
    //Set the scale bar to the newly referenced map frame
    scaleBar.SetMapFrame(mf);
}