There's a lot of blown bridges on that exterior section of taspir. Exactly which one? If you could be a little bit more specific it would make it easier for us to respond knowledgeably.
If I'm thinking of the same bridge as you are, I think you need to go back indoors. One of the big cubic boxes can be force pushed allowing you to enter the air duct system of the complex and from there you can make it to the next part of the level.
If I am way
off in my assumption and you're in a different part of the base, I hope this walkthrough will be of help: http://db.gamefaqs.com/computer/dosw..._academy_b.txt