View Q&A

We're looking at the design for the long span MGS and have a question about the three CRT posts on either side of the span.  These are shown as full depth wood posts, and we are considering an option to use steel foundation tubes and CRT post inserts, similar to post #2 in our attached Highway Standard 631011.  (The tube will be corrected to 6' for this downstream anchor terminal.)

Is the tube and stub post an allowable substitute for the full wood post used in the development of the long span MGS?

We would not recommend a stub and tube post setup for the CRT's used in the long span. The CRT's used in the long span are designed to rotate through the soil to some degree prior to fracture. In addition, it is common for the CRT posts to break at the second hole beneath the groundline when the post rotates in the soil. This behavior absorbs some of the kinetic energy from the vehicle impact and is important to the long span design's ability to transition from unsupported to fully supported guardrail.

The use of foundation tubes would reduce the rotation and energy absorption of the posts and prevent fracture of the lower hole in the post, thus changing the behavior of the system significantly. As such we cannot recommend them.