National Academies Press: OpenBook

Updating the AASHTO LRFD Movable Highway Bridge Design Specifications (2021)

Chapter: Chapter 4 Conclusions and Suggested Research

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Suggested Citation:"Chapter 4 Conclusions and Suggested Research." 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 49
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Suggested Citation:"Chapter 4 Conclusions and Suggested Research." 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 50

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49 C H A P T E R 4 Conclusions and Suggested Research Conclusions The preceding chapters detailed the proposed updates to the AASHTO LRFD MHBDS. A comprehensive literature review and survey of industry professionals were performed that guided this work. The primary objective was to develop a RBM that is consistent with LRFD design and apply where practicable. A proposed methodology was successfully developed that built upon the LRFD construct developed for the last major rewrite performed in 2000. Unfortunately, RBM application remains limited. Other controlling specifications such as the NEC and NFPA dictate design of substantial portions of the MHBDS (electrical and hydraulic design, respectively). Owner interviews provided mining data on approximately ¼ of the US movable highway bridge population. This data has been included herein and reveals that owners are generally satisfied with the historical performance of their movable bridges. With this knowledge, we were able to calibrate our RBM to existing design outcomes. Case studies were developed that illustrate excellent correlation between the existing design and proposed RBM design. Suggested Research A framework for future refinement and/or expansion of the design provisions has been successfully employed. Future work includes research into additional design components that could possibly incorporate the RBM. During the Phase I Literature Review, there were standards reviewed that contained topics beyond the current scope but were identified as candidates for future research. Those standards topics are: • DIN 19704-1:2014, Hydraulic Steel Structures, Part 1. German Standard, 2014: o This specification included design service life for several elements that are used in movable bridges. Investigate whether element-level service life values could be effectively applied to the MHBDS. Because the RBM was calibrated to provide similar outcomes to existing, incorporating design life for elements may be applicable as a reference table in commentary. However, additional owner feedback might indicate modified outcomes for various elements, which could be addressed with load or resistance modifiers. o Article 10:14 addressed factors for using manufacturer ratings for spherical plain bearings, an element not defined in the current AASHTO LRFD Movable. This item could be considered for addition to the MHBDS in Section 6 (similar to Article 6.7.7.2 - Rolling Element Bearings). Research would need to be performed to calibrate the factors to achieve desired outcomes.

50 • European Material Handling Federation (FEM) 1.001, Rules for the Design of Hoisting Appliances: o The document contained a detailed discussion of the factor of safety for wire ropes. Included was the “class of utilization and load spectrum” method of evaluation. This methodology is quite different than the RBM ultimately used. However, because wire rope selection remains mostly isolated and remains based upon factors of safety, it may be useful to further consider this approach to refine the MHBDS. Other suggested research includes review of limit state loading (Section 5) to account for new motors and electrical drives. This could also consider different loading for span operating prime movers versus prime movers for ancillary devices (i.e., span locks, end lifts, etc.).

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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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