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Suggested Citation:"Chapter 1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2021. Updating the AASHTO LRFD Movable Highway Bridge Design Specifications. Washington, DC: The National Academies Press. doi: 10.17226/26395.
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Page 2
Page 3
Suggested Citation:"Chapter 1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2021. Updating the AASHTO LRFD Movable Highway Bridge Design Specifications. Washington, DC: The National Academies Press. doi: 10.17226/26395.
×
Page 3
Page 4
Suggested Citation:"Chapter 1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2021. Updating the AASHTO LRFD Movable Highway Bridge Design Specifications. Washington, DC: The National Academies Press. doi: 10.17226/26395.
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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.

2 C H A P T E R 1 Introduction Background Design of movable highway bridges has traditionally utilized ASD methodology. In 2000, there was a major update to the AASHTO LRFD Movable Bridge Highway Design Specifications (MHBDS) that included reformatting many design equations into the LRFD format. However, due to lack of available data at the time, the factors utilized were essentially a rearrangement of the ASD formerly implemented. This effort has built on the work performed in 2000 and implemented a reliability-based methodology where possible to develop factors based on research including historical outcomes as reported from a wide range of movable bridge owners. Implementation of the LRFD approach is not practical for components that are controlled by other governing standards, including the National Electrical Code (NEC) and National Fluid Power Association (NFPA). In such cases, only general updates could be implemented for the electrical and hydraulic (Sections 8 and 7, respectively). Therefore, the research team focused on areas that could effectively implement the reliability-based methodology (RBM), which was Section 6 (Machinery Design). Load and resistance factors were updated in this section based on data collected from a wide variety of bridge owners. The data was statistically analyzed by Auburn University to develop new load and resistance factors. In addition, Section 5 (Mechanical Design Loads and Power Requirements) was updated to allow owners the option of applying the traditional wind loading or a site-specific wind loading. Research Objective The objectives of this research included: 1. Develop and incorporate a consistent RBM into the existing AASHTO LRFD MHBDS concentrating on design of: mechanical, electrical, hydraulic and traffic/navigation safety systems. 2. Propose revisions to the AASHTO LRFD MHBDS, including all sections. The vision of the research team was to provide AASHTO with an updated specification that applies RBM where feasible. The specification was updated with the understanding and intent that the document would be revised and improved periodically in concurrence with the future state of practice.

3 Research Approach The aforementioned research objectives were executed over a period of four phases made up of a total of 13 tasks. The main aspects of the project included • A review and synthesis of literature; • A survey of current industry practice in relation to movable bridge design (including other foreign standards); • The survey and interview of diverse movable bridge owners and analysis of data collected: • The proposal, development, and execution of a reliability-based design methodology; • The integration of RBM and general updating of the specification, and • The development of the case study. The information gained from both the literature review and surveys were used to develop a proposed RBM concentrating on mechanical design. The RBM included calibrating outcomes according to historical performance as obtained through the owner surveys and interviews. It was determined that the RBM could not effectively be applied to electrical, hydraulic and traffic/marine safety devices, as they are all subject to other governing design guidelines such as the NEC, NFPA, and MUTCD. Even for mechanical design, there were specific components that were similarly governed by other standards such as gearing (AGMA), anti-friction bearings (ABMA), and wire ropes (various federal and industry standards). Contents of the Updated Specification The updated specification maintained its existing organization. General updates were made to the entire specification. Substantial changes were made to Section 5 where the owner now has the option to utilize site-specific wind loading. Wind loading is a major contributor to sizing of the operating machinery, especially for bascule and swing bridges. Section 6 includes implementation of the RBM with updated and calibrated load and resistance factors. A new appendix is included that provides a framework for applying a system-wide methodology to evaluate relative reliability for a particular bridge (i.e., these are not considered absolute reliability evaluations but are intended to provide the owner/designer a methodology to evaluate options for a particular bridge site). The contents of the updated Specification are organized as follows: • Section 1—General Provisions • Section 2—Structural Design • Section 3—Seismic Design • Section 4—Vessel Collision Considerations • Section 5—Mechanical Design Loads and Power Requirements • Section 6—Mechanical Design • Section 7—Hydraulic Design • Section 8—Electrical Design

4 • Appendix A: SI Versions of Equations, Tables, and Figures • Appendix B: System Reliability Considerations

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Updating the AASHTO LRFD Movable Highway Bridge Design Specifications Get This Book
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There are approximately 1,000 movable highway bridges in the U.S. inventory.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 314: Updating the AASHTO LRFD Movable Highway Bridge Design Specifications allows bridge owners the option of employing site-specific conditions to develop the design wind speed and provides other general updates to previous research from 2000 that reflects changes in design practice and other standards.

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