National Academies Press: OpenBook

Guidelines for Shielding Bridge Piers (2018)

Chapter: Chapter 7 - Conclusion

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Page 92
Suggested Citation:"Chapter 7 - Conclusion." National Academies of Sciences, Engineering, and Medicine. 2018. Guidelines for Shielding Bridge Piers. Washington, DC: The National Academies Press. doi: 10.17226/25313.
Page 92

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92 Conclusion The preceding chapters have presented bridge pier protec- tion guidelines proposed for inclusion in both the AASHTO LRFD Bridge Design Specifications and the RDG. Procedures, background regarding the development of those procedures, example problems, and comparisons to RSAPv3 have been presented. In the LRFD Bridge Design pier protection procedures, the user proceeds by looking up site-specific values in four tables and then inserting these values into a short calculation to determine the annual frequency of bridge collapse. If that value is less than 0.001 for a typical bridge or 0.0001 for a critical bridge, the pier system need not be shielded. These acceptance criteria values can be modified by AASHTO or adopting states should they want to make the criteria either more or less conservative. The proposed LRFD pier protection guidelines describe what types of pier systems need to be evaluated for shielding and also provide lateral capacity suggestions. If a shielding barrier is required, it must be a MASH crash-tested TL-5 rigid concrete barrier positioned on the site according to RDG Section 5.6.4. Additionally, a minimum 60-ft TL-5 rigid con- crete barrier should be provided in advance of the leading pier component. Reference has been made to the RDG to ensure conflict between publications is not created. The 60-ft minimum is suggested to ensure that, regardless of how the length-of-need calculations are presented in the RDG in the future, the LRFD will include the minimum barrier necessary to redirect a heavy vehicle. Similarly, for the passenger-vehicle occupant protection procedures, the user proceeds by looking up site-specific val- ues in three tables, then uses those values in a short calculation to determine the annual number of severe and fatal injury crashes. If that value is less than 0.0001 severe or fatal injury crashes per year, then the pier system need not be shielded for occupant protection. These criteria can be modified by AASHTO or adopting states should they want to make the criteria either more or less conservative. If a shielding bar- rier is required for passenger-vehicle occupant protection, a MASH crash-tested TL-3 w-beam guardrail positioned on the site according to RDG Section 5.6.4 is suggested. Four example problems were presented that illustrate the application of both the LRFD and RDG procedures and com- pare the results to RSAPv3 simulations. The results of the pro- cedures compare closely with the RSAPv3 estimates. C H A P T E R 7

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TRB’s National Cooperative Highway Research Program (NCHRP) Research Report 892: Guidelines for Shielding Bridge Piers provides proposed load and resistance factor design (LRFD) bridge design pier protection specifications and proposed occupant protection guidelines. Bridge piers are generally close to the roadway to minimize bridge lengths. As a consequence, barriers are normally placed around piers to reduce the potential of vehicle crashes damaging the piers. However, the design and placement of the barriers may not have taken into consideration the possibility that vehicles, particularly large trucks, might still impact the pier. The report also includes four examples that illustrate the use of the proposed specifications and guidelines for shielding bridge piers.

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