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In our current specifications we do not permit the mixing of wood and steel post within a run of beam guard.  I have not found published guidance indicating that the mixing of steel and wood post is a problem.  Is there an issue in mixing wood and steel post within a run of beam guard?  My first guess is that the wood and steel post react differently during an impact and mixing them could cause a potential pocketing situation, but I don't know for sure.

We require the EATs and the Thrie Beam Structure Approaches to use only wood post.  This can lead to wood being installed at the ends of a beam guard run that uses steel posts.  If we shouldn't allow the intermixing of wood and steel within a beam guard run, switching back to wood for the EAT and the Thrie Beam Structure Approach appears to be problematic.

For the EAT, I could see that we need the post to fail during a head on impact with the EAT and therefore break a way post would be needed.  I just don't know if there is a similar argument for the Thrie Beam Structure Approach.

Any insight that MwRSF could provide would be greatly appreciated.

Generally speaking, W-beam guardrail systems have been crash tested with one post type placed throughout the major length of the barrier system. For each test, either wood posts or steel posts were likely used and not the combined or alternating use of wood and steel posts within the impact region. Many of these W-beam barrier systems have been found to have similar dynamic performance. If barrier performances were found to be similar when using the steel and wood posts, then I would not be too concerned with allowing the replacement of damaged posts with a post of an alternative material type, wood for steel and steel for wood assuming the post performances were found to be similar. For approach guardrail transitions, the same general philosophy would be used, but it is important to try to match the post-soil behavior to that used in the original system. For guardrail end treatments, the use of alternative post materials should be addressed by the manufacturer since most of these systems are proprietary.