Dead player ragdolls just fly through props

Whenever I’m noclipping and used the kill command, my ragdoll can just fly through any props. How do I fix this?

Also I can’t use L4D stuff.

You don’t. That’s just part of how the source engine works.

You can’t use L4D stuff because L4D runs on a newer engine that Gmod

There are add-ons that add L4D and L4D 2 models to Garry’s Mod