Problem Statement
For roadway Type 2 strong post details across low-fill culverts and small structures or underground obstructions where proper post embedment cannot be achieved, either long span guardrail or steel post over underground structures similar to the details below are desirable.
If deflection tolerance is limited due to existing tight lateral restrictions, the steel post over underground Structures detail can be specified. However, there has been no physical crash testing of this system for the intended NCHRP Report 350 Test Level 3 requirements. Moment slabs can become an expensive alternative to most local municipalities that might use a detail such as the one shown above. Therefore, there is a need for a more cost effective design for this situation.
Background
As part of this pooled fund program, a w-beam guardrail system using W6x9 steel guardrail post was anchored to a simulated concrete box culvert and crash tested. The height of the fill used on top of the box culvert was 9.0 inches. The results of the crash test were successful with respect to NCHRP Report 350 requirements for Test Level 3. For this project, design and crash information obtained from the steel post anchored to the box culvert project will be used for this project. Information from this study as well as design and pendulum testing on a shallow moment slab anchoring an isolated W6x9 guardrail post will be used to develop a steel post supported by a shallow moment slab for use over underground structures.
Objective
Develop a steel post design utilizing a shallow moment slab for Type 2 strong post guiderail that can be placed over low-fill culverts or other buried structures where low deflection limits apply. This system would be crash tested and meet the minimum requirements for NCHRP Report 350 requirements, Test Level 3.
Benefits
This project would develop a practical design that meets the minimum requirements of NCHRP Report 350, Test Level 3. It would be a viable alternative for supporting a guardrail post where shallow underground obstruction(s) exist. It would save cost compared to a larger moment slab supporting several guardrail posts.
Question for Pooled Fund States
Greetings All,
I am working on the pooled fund project “Steel Posts Over Underground Structures.”
I have a few questions that I would like your feedback on.
PennDOT has used the following details, but I understand this design has never been tested:
PennDOT details for steel posts over underground structures
Question: Does your state have any similar details that we can consider for this project? If so, could you send me your state’s details?
Question: Do you have any specific design information you would like to see incorporated into the design we plan to develop for this project?
Please let me know.
Your assistance in this matter is appreciated!
Thanks!
William Williams, P.E.
Asst. Research Engineer
Texas Transportation Institute
Texas A&M University System
979-862-2297 off.
979-845-6107 fax
w-williams@tamu.edu
Final Report
Executive Summary
Videos of Pendulum Testing
Pendulum Test on 60-inch Slab
Pendulum Test on 48-inch Slab
