When your portal session expires, by defalut you get a message saying that
Your portal session has timed out because of no activity. Please start a new session at your portal Home.
In scenarios where you want user to redirect to login screen or custom page after session expires, there you will need to add custom property to WP Configservice.
Here yo go....
1) Login to WAS as admin
2) Navigate to Resources - >Resource environment - > Resource environment providers
3) Click on WP ConfigService
4) Click on Custom properties
5) click on New
6) provide redirect.logout to name field
7) provide true to value field
8) click Ok
9) cick new again to add another property
10) provide redirect.logout.url to name field
11) provide /wps/portal to value field (this will bring up login portlet after session time out. You can also provide custom url to redirect users to custom screen after session time out)
12) click ok and
13) Save configuration