the easiest way is to change your working calendars ot reflect the shutdown. for each calendar used (shouldn't be too many as a rule) just add non working tome to cover the period. You dont have to split anything, as project will automatically span it.
If you want to how the shutdown as an activity, enter it as a task with a "must start on" start date, and put in in as edays. this will then cover the period with an actual activity that will not affect anything else.