Welcome to the forum.
Here is what The Columbia Guide to Standard American English (1993) has to say:
There are two main classifications of sentences, one based on grammar (i.e., on the number and kinds of clauses they contain), the other based on rhetorical purpose or meaning. The grammatical sentence types are four: simple, compound, complex, and compound-complex. The meaning-based types are three: statement, question, and command (also called declarative, interrogative, and imperative).[/i]
What I have to say is that imperative sentences can end with either a period OR an exclamation mark. If an imperative sentence ends with an exclamation mark, then the sentence is both imperative and exclamatory.
But the sentence type (according to my the above quote) would be only imperative.