There are better workarounds in this thread, but if you get stuck with a EXP/IMP .dmp file that won't import do to a virtual column, it is possible to tweak the file to reimport as a physical column if you really need the data in there.
If you text search for the "CREATE TABLE" statement, there should be alters that try to make the column virtual (bolded). Deleting those lines will allow you to IMP the table data, though you will still need to deal with the structure of the virtual column afterwards:
CREATE TABLE "mytable" (
"column1" VARCHAR2(30) NOT NULL ENABLE,
<storage parameters here> ALTER TABLE "TABLESPACE_MIGRATIONS" MODIFY DEFAULT
*<special characters>ALTER TABLE "TABLESPACE_MIGRATIONS" MODIFY ("VIRTUALCOLUMN" DEFAULT <expression/function for virtual column>)*
INSERT INTO "mytable" ...