Bridge Railing Design Requirements (2024)
Chapter: Summary
SUMMARY
Bridge Railing Design Requirements
The two main objectives of this research project were to rewrite and update the entirety of Section 13, Railings, of the AASHTO LRFD [Load and Resistance Factor Design] Bridge Design Specifications (AASHTO LRFD BDS) and to provide examples comparing updated railing design loads and analysis procedures with those in the current Section 13 (AASHTO 2020a).
The research approach to the first objective included a literature review and synthesis, followed by recommending changes to loads and analysis procedures for the design of traffic railing crash-test articles, based on the state of knowledge. Loads and load application heights and lengths were updated for each Test Level (TL) in the AASHTO Manual for Assessing Safety Hardware (MASH) (AASHTO 2016), using data from NCHRP Web-Only Document 326: Design Guidelines for Test Level 3 through Test Level 5 Roadside Barrier Systems Placed on Mechanically Stabilized Earth Retaining Walls (Bligh et al. 2017). Loads from MASH Test Levels trend higher when compared to those from NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features (Ross et al. 1993), but when combined with changes to load application heights and lengths, the overall change to load effects is minimal. There is an increased emphasis that the provided loads and load application criteria are for crash-test specimens and not required for railing strength. Treatment-of-strength requirements for traffic railing are unique for bridge elements in that they are performance-based, with criteria established in MASH, which also has criteria for occupant safety crashworthiness. Both strength and occupant safety criteria must be met for railing crashworthiness.
Revisions to the recommended yield-line analysis procedures were made based on the state of knowledge, which trended with less conservatism than the yield-line method in the current Section 13. This applies to concrete barriers; analysis procedures for other railing types remained unchanged due to a lack of significant changes in the state of knowledge. Other content was updated and condensed to complement relevant sections of AASHTO LRFD BDS.
Last, Section 13 incorporates results and recommendations from two other NCHRP research projects. Recommendations are included from NCHRP Research Report 1024: Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance (Williams, Schulz, and Abu-Odeh 2022) addressing and updating traffic railing geometry in the rewritten Section 13. NCHRP Research Report 1078: MASH Railing Load Requirements for Bridge Deck Overhang (Steelman et al. 2023) investigated bridge deck overhang requirements related to MASH crash-test criteria and contributed relevant content to the rewrite of Section 13.
