National Academies Press: OpenBook

MASH Railing Load Requirements for Bridge Deck Overhang (2023)

Chapter: Chapter 1 - Introduction

« Previous: Summary
Page 3
Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 3
Page 4
Suggested Citation:"Chapter 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 4

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

3   Introduction Background As of January 1, 2020, all new and replacement bridge rails installed on the National High- way System are required to conform to the crash testing criteria in the Manual for Assessing Safety Hardware, 2nd Edition (MASH) (1). Currently, however, the bridge rail guidance provided in AASHTO LRFD [Load and Resistance Factor Design] Bridge Design Specifications (AASHTO LRFD BDS) (2) reflects the requirements of the preceding crash testing standard, NCHRP Report 350 (3). The conversion from NCHRP Report 350 to MASH 2016 criteria is accompanied by increases in expected vehicle impact severities for test levels 1 through 4. From the designer’s perspective, these increases manifest as increased lateral and vertical design loads imposed on bridge rail systems. The integrity of any bridge rail system is heavily dependent upon the deck structure to which it is secured. The design of the deck structure is ultimately of equal importance to that of the bridge rail as either can limit the strength of the overall system in the event of a vehicle impact. Further, repairs to bridge deck overhangs are considerably more costly than those of bridge railings. The bridge deck overhang is the cantilevered portion of the bridge deck protruding from the outermost girder and, for some railing types, is particularly sensitive to railing impacts. As such, increased design impact loads affect not only the design of the bridge rail system but also the bridge deck overhang as well. Objectives The primary objective of this research effort was to propose modifications to the deck over- hang evaluation methodology of AASHTO LRFD BDS (2). Individual objectives included: • Characterizing the pattern by which impact loads distribute longitudinally with downward transmission through the railing and with inward transmission through the overhang. • Identifying slab failure mechanisms and refining capacity evaluation methods for overhangs supporting posts. • Developing design methodologies for overhangs supporting various railing types. • Developing examples demonstrating the application of the proposed modifications. Methodology For each railing type, the general methodology used to develop proposed modifications to the AASHTO LRFD BDS included: 1. Surveying state agencies and conducting a literature review to identify designs and damage types. C H A P T E R 1

4 MASH Railing Load Requirements for Bridge Deck Overhang 2. Performing preliminary analytical modeling to plan test specimens. 3. Conducting physical tests of instrumented test specimens. 4. Using results of instrumented test specimens to calibrate analytical models. 5. Expanding analytical models to evaluate the behavior of design variations. 6. Developing a design methodology based on a data pool created in Steps 3 and 5 (2). Scope Cast-in-place concrete overhangs supporting concrete barriers as well as open concrete top- mounted and curb-mounted steel railings were considered in this research effort. As barriers compose the majority of railings in the U.S. inventory, emphasis was placed on overhangs supporting that railing type. Skewed and curved bridges were not considered.

Next: Chapter 2 - Overview of LS-DYNA Modeling Practices »
MASH Railing Load Requirements for Bridge Deck Overhang Get This Book
×
 MASH Railing Load Requirements for Bridge Deck Overhang
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

State highway agencies across the country are upgrading standards, policies, and processes to satisfy the 2016 AASHTO/FHWA Joint Implementation Agreement for MASH.

NCHRP Research Report 1078: MASH Railing Load Requirements for Bridge Deck Overhang, from TRB's National Cooperative Highway Research Program, presents an evaluation of the structural demand and load distribution in concrete bridge deck overhangs supporting barriers subjected to vehicle impact loads.

Supplemental to the report are Appendices B through E, which provide design examples for concrete barriers, open concrete railing post on deck, deck-mounted steel-post, and curb-mounted steel-post.

READ FREE ONLINE

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!