Struts has nothing to do with regulating sessions. It's just a framework that runs within a J2EE Web Container.
It is the application server's job to regulate sessions and each individual server does it a little differently. In order to answer this question, you will need to consult the documentation for the application server that you're using.
A session facade has nothing to do with HttpSessions. A session facade is a J2EE pattern that has to do with EJB session beans, which is an entirely different topic.