The language of "Section 13: Railing" of the AASHTO LRFD Bridge Design Specifications has not had a major revision since the load and resistance factor design (LRFD) specifications were adopted. Some of the text date back to the 1989 AASHTO Guide Specifications for Bridge Railings. Since that time, the Manual for Assessing Safety Hardware (MASH) has replaced NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features for evaluating safety hardware devices. A joint AASHTO/FHWA implementation agreement for MASH was signed on January 7, 2016 requiring all new permanent installation and full replacement of bridge rails on the national highway system in contracts letting after December 31, 2019 to be compliant to MASH.
Therefore, there is an immediate need to update the Section 13 of the AASHTO LRFD Bridge Design Specifications in order to incorporate the MASH requirements and address outdated language and areas of ambiguity particularly related to: loads, load distribution to bridge barriers and deck overhangs, and analysis methods for determining the demand and capacity of bridge barriers.
The objectives of this research are to (1) rewrite the entire "Section 13: Railing" of the AASHTO LRFD Bridge Design Specifications and (2) develop examples to demonstrate the application of the proposed rewritten section. At the minimum, the rewrite of Section 13 shall focus on new developments related to loading requirements of the AASHTO MASH and analysis methods for designing bridges to meet the MASH requirements.
Accomplishment of the project objectives will require at least the following tasks.
Task 1. Conduct a literature review of relevant domestic research considered to be the state-of-the-practice in testing, evaluating, and designing of bridge railing. The review shall include published and unpublished research conducted through the NCHRP; FHWA; and other national, state, and pooled-fund sponsored research.
Task 2. Synthesize the literature review to identify the knowledge gaps for bridge railing design. These gaps should be addressed in the proposed rewritten section or in the recommended future research as budget permits.
Task 3. Propose methodology including evaluation criteria to select the loading requirements and analysis methods that will be implemented in the rewrite of Section 13 as there are currently different loading requirements and analysis methods based on existing research. The research shall consider the application of barrier on mechanically stabilized earth (MSE) walls and other wall types.
Task 4. Propose an annotated outline for the rewrite of Section 13 and identify other sections of the AASHTO LRFD Bridge Design Specifications that require modifications. The rewrite shall include the existing appendix of Section 13 and adding NCHRP Report 350 as an appendix.
Task 5. Prepare Interim Report No. 1 that documents Tasks 1 through 4 and provides an updated work plan for the remainder of the research. This report must be submitted no later than 4 months after contract execution. The updated plan must describe the process and rationale for the work proposed for Phases II and III.
PHASE II—Rewrite of Section 13 and Examples
Task 6. Execute the approved work plan related to Task 3 and select the loading requirements and methods of analysis to be implemented in the rewrite of Section 13. Develop examples for design of bridge railing with consideration of the following:
- Concrete and metal railing;
- Interior and exterior regions of railing; and
- Deck overhangs.
The examples shall include a comparison between the current and newly proposed loading requirements and methods of analysis. Submit a letter report at the end of Task 6 for NCHRP review no later than 6 months after approval of Phase I.
Task 7. Rewrite Section 13 according to the approved Interim Report No.1 including proposed modifications to related sections of the AASHTO LRFD Bridge Design Specifications. The draft section should be publication-ready (i.e., AASHTO-style) format with appropriate level of detail.
Task 8. Prepare Interim Report No. 2 that documents Tasks 6 and 7 and provides an updated work plan for the remainder of the project. This report must be submitted no later than 12 months after approval of Phase I.
PHASE III—Final Products
Task 9. Revise the proposed Section 13 taking into account feedback from the NCHRP project panel and prepare a ballot item for the AASHTO Committee on Bridges and Structures.
Task 10. Prepare final deliverables including: (a) a final report that documents the entire research effort and (b) the proposed Section 13, examples, and implementation plan.
STATUS: Research in progress
The research team is awaiting the completion of NCHRP 12-119. Findings from NCHRP 12-119 and 22-35 will be incorporated into the recommendations for the re-write of Section 13 of the AASHTO LRFD BDS.