National Academies Press: OpenBook
« Previous: Front Matter
Page 1
Suggested Citation:"Summary ." National Academies of Sciences, Engineering, and Medicine. 2017. Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads. Washington, DC: The National Academies Press. doi: 10.17226/24840.
×
Page 1

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.

1 S u m m a r y This report presents a comprehensive research program dedicated to bridges carrying light rail transit loading, including those subjected to both light rail and highway traffic loadings. The research is composed of two phases: a state of the art review and technical investigations. Of interest are the behavior of light rail bridges, live loads and associated forces, rail–train–structure interaction, and load factor calibration to implement the Load and Resistance Factor Design (LRFD) method. Technical findings are used to develop guide specifications, which complement the contents of the AASHTO LRFD Bridge Design Specifications (BDS). Light rail bridges are designed to accommodate the AW4 design category, consisting of train weight and fully occupied passengers, in conjunction with embedded, ballasted, and direct fixation tracks. A number of research projects have been conducted to examine the behavior of rail bridges, whereas most of them are concerned with conventional heavy-haul and high-speed trains. Limited information is available on the response of bridges subjected to light rail transit. Existing design guidelines for light rail bridges are developed with agency- specific live loads or based on the provisions of AASHTO LRFD BDS and the American Railway Engineering and Maintenance of Way Association (AREMA). Technical discrepancy exists, because AASHTO LRFD BDS and AREMA are not related to light rail transit loadings. Although the existing guidelines are useful and provide valuable sources for the design of light rail bridges, there is no consensus in many occasions [e.g., dynamic load allowance (DLA) or impact varies from 10% to 40% of a static load]. Two design philosophies are currently implemented in the light rail bridge community, namely, the LRFD and Allow- able Stress Design (ASD) methods. In the case of agencies adopting the LRFD approach, load factors are directly taken or modified from AASHTO LRFD BDS. Refined calibration is required for light rail bridges, since the characteristics of light rail transit are different from those of highway traffic. The behavior of five constructed bridges is monitored when subjected to light rail trains, with an emphasis on in situ train loadings, girder strains, displacements, dynamic charac- teristics, live load distributions, and multiple presence events. Finite element models are formulated to study various aspects associated with light rail bridges, such as flexural and shear responses, DLA, live load distributions, deflections along with user comfort, centrifu- gal and longitudinal forces, thermal loading, rail break, and the effect of combined light rail and highway traffic loadings. A standard live load model is developed to generate uniform design outcomes, regardless of transit agency. Load factors are calibrated, particularly for the strength and fatigue limit states of light rail bridges. Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads

Next: Chapter 1 - Introduction »
Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB's National Cooperative Highway Research Program (NCHRP) Research Report 851: Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads provides proposed specifications for bridges carrying light rail transit loading, including those subjected to both light rail and highway traffic loading. The proposed specifications and design examples are based on comprehensive response monitoring of five bridges carrying light rail transit vehicles in Denver, Colorado, and analytical programs for investigating the behavior of light rail bridges, live loads and associated forces, rail–train–structure interaction, and load factor calibration to implement the Load and Resistance Factor Design (LRFD) method. A standard live load model generates uniform design outcomes for any transit agency. Load factors are calibrated, particularly for the strength and fatigue limit states of light rail bridges.

  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!