I am having a doublt regarding hot sustaind stress check.
Please any body can through a light why it is required?
In general what we do is remove the liftup support and check the stress and clear the system.
If we are doing hot sustaind stress supports are deloaded (means it take the operating loads)this indented for higher sustaind stress

See this overview of the proper way to evaluate Sustained stresses.

Note, this article can be found in the "Technical Articles\CAESAR II" section of this web site.