Sum of Multiple Date Ranges



I am trying to find the sum of Net Work Days between three date ranges. 

Expected Dock Date  &  Dock Date

Available for QC   &   QC Complete

Date Received into Sage  &  Expected Receipt

This formula isn't quite working.  It may be that not every one of these dates has been populated yet, but ideally it would be a + or - number value.

=SUM(([Dock Date]1,[Expected Dock Date]1) + ([Available for QC]1,[QC Complete]1) + ([Expected Sage Receipt Date]1,[Date Received into Sage]1)