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Bridge over a road

Service Limit State Design for Bridges.

Service Limit State Design for Bridges (R19B)


Bridge components deteriorate at different rates, which can lead to unanticipated bridge closings. Under the current system, bridge components are planned based on "ultimate limit state performance," which does not take into account service limit states focused on longevity-driven and durable design.


SHRP2's Service Limit State Design for Bridges toolkit offers a quantitative framework to assess service limit states more accurately. The toolkit provides actual performance data, component-based distress models, and specific guidance for common bridge elements, as well as:

  • A framework for calibrating service limit state specifications.
  • Service limit state load and resistance factors.
  • Bridge design procedures and model specifications for service limit states.
  • Tools required for future service limit state improvements.
  • Model specification changes that include designing for durability.

The toolkit contains databases, software tools used in the calibration (such as Monte Carlo spreadsheets), and instructions for developing new or revised spreadsheets and deterioration models.

The framework will calibrate the following AASHTO service limit state design elements:

  • Live load deflections
  • Bearing movements
  • Settlement of foundations and retaining structures
  • Permanent deformations of compact steel components
  • Fatigue of structural steel and the steel reinforcement in concrete (complementary research being conducted through the National Cooperative Highway Research Program [NCHRP] 12-83)
  • Slip-critical bolted connections
  • Concrete approaches


Improved service limit state design can increase the service life of bridge components and give designers the option to select bridge components based on expected maintenance time and difficulty of replacement.

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