Q:

unable to truncate a parent table even after disabling a FK constraint in sql server

I am unable to truncate from a parent table by only disabling the FK constraint in the referring table . I had to actually drop the constraint in the referring table to be able to truncate the parent table. 
I did the above step after first truncating the child table.....so I did follow the right order....do i really need to delete the constraint and then bulk insert the data and then re-create the FK constraint?

A:

If you wanna use TRUNCATE then yes, dropping and recreating the constraint is the only way.
Confirmation in doc (with more explanations)

You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY
  constraint; instead, use
  DELETE statement without a WHERE clause. Because TRUNCATE TABLE is not
  logged, it cannot activate a trigger.

