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Developing of Fragility Curves for Multi-Span Precast Girder Concrete Bridges in Seismic Regions


There are significant number of multi-span precast girder concrete bridges in high seismic regions and long duration earthquakes that have been designed and constructed at a time when seismic resiliency requirements were nonexistent or inadequate by today's standards. To avoid bridge collapses, reduce the risk of extensive damage in future earthquakes, and most effectively allocate the financial resources, the vulnerability of bridges to earthquakes must be identified by developing appropriate fragility curves with consideration to bridge superstructure, substructure and foundation complexity. The fragility curves are required to relate the hazard to the likelihood of bridge closure as the expansion joints open and to collapse when the opening becomes too large. These curves should relate spectral acceleration and spectral displacement to the likelihood of collapse for different structural periods and for different structure types.

Fragility curve is one of the widespread methods used in seismic evaluations of existing bridges. The fragility curves provide conditional statements of probability of a bridge reaching or exceeding a particular damage level for a given intensity level. The fragility analysis generally includes simulation of bridge, simulation of ground motions, and generation of fragility curves from the seismic response data of the bridge models. The seismic response data can be obtained from elastic spectral analysis, or nonlinear static analysis, or nonlinear time history analysis. There is a need to determine fragility curves to capture the seismic vulnerability of multi-span precast girder concrete bridges per SGS and for long duration earthquakes specific to the Pacific Northwest.


The objective of this research is to develop fragility curves to capture the vulnerability of multi-span precast girder concrete bridges in long duration earthquake regions and associated seismic hazards. The first step in this effort would be to address the collapse vulnerability of multi-span precast girder concrete bridges. The support length is required, but the relative stiffness of adjacent frames, pier skews, and abutment types effects cannot be readily captured for each bridge. The following steps will be considered in this proposed research project:

  1. Domestic and international literature study to determine current state of knowledge on fragility curves of multi-span precast girder concrete bridges in long duration earthquake regions.

  2. Identify parameters that need to be considered to accurately predict the seismic hazards due to end and in-span support unseating, pier skews, and abutment types.

  3. Develop a range of fragility curves that relate ground motion to increased probability of collapse for different periods and different bridge types as more states transition to displacement-based design. Test fragility curves using database of bridge inventories and bridge damage from previous earthquakes.

  4. Submit a final report including design guidelines and design examples demonstrating that fragility curves can be used for multi-span precast girder concrete bridges in mega and long duration earthquake regions.


Currently there is little work on calculating the probability and risk of multi-span precast girder concrete bridges in long duration and mega earthquakes despite it being the most common cause of bridge collapse. Therefore, this research can be seen as addressing three topics in the AASHTO Highway Subcommittee on Bridges and Structures “Grand Challenges: A Strategic Plan for Bridge Engineering”:

· Grand Challenge 1: Extending Service Life

· Grand Challenge 2: Optimizing Structural Systems

· Grand Challenge 4: Advancing the AASHTO Specifications

This project should be implemented through NCHRP.

Related Research:

Literature Search Summary

The proposed research differs from the existing body of research found in a review of relevant literature. None of the available literature match the title or address the objectives of the proposed research statement in the suggested websites:

TRID (http://trid.trb.org)

  1. PROJECT: Performance of Existing ABC Projects – Inspection Case Studies (University of Washington), Accelerated Bridge Construction University Transportation Center (ABC-UTC), $70000, 2019, Active2019-01-01

Comparison of Curved Prestressed Concrete Bridge Population Response Between Area and Spine Modeling Approaches Toward Efficient Seismic Vulnerability Analysis Engineering Structures, Volume 150, Issue 0, 2017, pp 176-1892017-11-01

  1. Vulnerability Sensitivity of Curved Precast-Concrete I-Girder Bridges with Various Configurations Subjected to Multiple Ground Motions, Journal of Bridge Engineering, Volume 22, Issue 2, 2017, Content ID 040161182017-02



  1. PROJECT: Performance of Existing ABC Projects – Inspection Case Studies (University of Washington), Accelerated Bridge Construction University Transportation Center (ABC-UTC), 2019

Implementation Considerations

State DOTs and transportation agencies Bridge engineers, and asset managers and planners will be using the research results.

State DOTs can implement the research within their own organization through asset management identifying bridges in immediate need for retrofit.

Categorizing bridges per their type, size and location seismicity could be used to support implementation.

Additional products such as presentations, training workshops, peer exchanges, and webinars will help create awareness and facilitate implementation of the research results.

AASHTO Committee(s) T-3 seismic and T-9, and T-18 – and precast concrete organization might be interested in the research results and could help support implementation.

Bijan Khaleghi, (360) 705-7181, Bijan.Khaleghi@wsdot.wa.gov; Amy Leland, Amy.Leland@wsdot.wa.gov; Jerry Shen, jia-dzwan.shen@dot.gov; and Anthony Mizumori, Anthony.Mizumori@wsdot.wa.gov



Sponsoring Committee:AKB50, Seismic Design and Performance of Bridges
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Bijan Khaleghi, PhD, PE, SE (WSDOT); Amy Leland, PE, SE (WSDOT); Anthony Mizumori, PE, SE (WSDOT)
Source Info:Problem Statement Author(s):

Bijan Khaleghi, PhD, PE, SE
State Bridge Design Engineer
WSDOT, Bridge & Structures Office
Olympia, WA 98504-7340

Amy Leland, PE, SE
State Bridge Seismic and Foundation Specialist
WSDOT, Bridge & Structures Office
Olympia, WA 98504-7340

Anthony Mizumori, PE, SE
State Bridge Concrete Specialist
WSDOT, Bridge & Structures Office
Olympia, WA 98504-7340

Potential Panel Members:
State DOTs seismic specialists, bridge designers, universities and consultants specialized in seismic performance of bridges
Date Posted:11/02/2021
Date Modified:11/16/2021
Index Terms:Girder bridges, Precast concrete, Concrete bridges, Fragility curves, Bridge design, Seismicity, Earthquake resistant design,
Cosponsoring Committees: 
Bridges and other structures

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