Project Title/ID Number Performance Assessment of Highway Overpasses—5392003
Start/End Dates 10/1/03—9/30/04
Project Leader Bozidar Stojadinovic (UCB/F)
Team Members Kevin Mackie (UCB/GS), Kyungkoo Lee (UCB/GS), Meghann Rand (UCB/GS)

F=faculty; GS=graduate student; US=undergraduate student; PD=post-doc; I=industrial collaborator; O=other

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1. Project Goals/Objectives:

The goal of this project is to provide the tools for performance assessment of highway overpass bridges. Such tools enable assessment of bridge performance in terms of the potential for bridge collapse in an earthquake, cost of repair of such a bridge after an earthquake, and the ability of the bridge to carry a given level of traffic load after an earthquake. The intended users of such tools are bridge engineers and highway system maintenance and emergency management professionals. Using these tools, the engineers can assess the effect of different design decision on performance of the overpass, while emergency management personnel can investigate potential earthquake scenarios to plan for highway system emergencies before an earthquake and obtain a quick estimate of potential bridge performance bottlenecks immediately after an earthquake.

2. Role of this project in supporting PEER’s mission (vision):

The result of this project will benefit PEER industry partners involved in bridge design and highway network maintenance and risk assessment because it will give them a tool to estimate performance of highway overpass bridges. This tool may be integrated into high-level applications that assess the performance of highway networks enabling emergency scenario planning and decision making at the level of an urban region.

3. Methodology Employed:

The tool for performance assessment of highway overpass bridges is base directly on the PEER probabilistic performance-based design methodology epitomized in the PEER total probability integral. The bridge performance-based assessment tool is based on bridge fragility curves providing a total probability of exceeding a chosen Damage Measure or Decision Variable level.

4. Brief Description of past year’s accomplishments (Year 6) & more detail on expected Year 7 accomplishments:

During Year 6 of this project we completed work on choosing optimal earthquake Intensity Measures for highway overpass bridges. We also completed the probabilistic demand models for typical highway overpass bridges (the IM-EDP relations) with respect to a large number of bridge parameters, such as number of spans, bridge aspect ratio, amount or reinforcement and abutment modeling. We also incorporated the probabilistic damage models (EDP-DM) relations developed by Professor Eberhardt for PEER

During Year 7 we are developing direct and indirect loss models for bridges. Direct loss models estimate the cost or repair of bridge components with respect to the bridge replacement cost. Indirect loss models estimate the ability of a bridge to function after an earthquake in terms of its ability to carry traffic and in terms of its remaining lateral and gravity load strength. Sample direct and indirect loss model and resulting bridge fragility curves are shown below.

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Fig 1 Sample component loss model Fig 2 Component level decision fragility
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Fig 3 Sample bridge loss model Fig 4 Bridge level decision fragility

5. Other Similar Work Being Conducted Within and Outside PEER and How This Project Differs:

A major project on the development of a risk-based methodology for assessing seismic performance of highway systems, conducted in cooperation between MCEER and USC, is similar to this project. The differences are:

  1. The fragility curves developed in this project will be based on PEER probabilistic performance-based methodology and developed using sophisticated non-linear bridge computer models, while the USC/MCEER project uses simplified bridge models or empirical fragility curves;
  2. USC/MCEER project has a significantly wider aim; while this project is focused on rational evaluation of bridge post-earthquake operational state, repair time and cost, and aftershock collapse risk.

This project is vertically linked to PEER bridge test-bed projects: Humboldt Bay Bridge, I-880 Bridge, and Bay Area Highway Network. Work on this project depends on the results of several PEER projects. In particular, it is horizontally linked to bridge component database projects (Eberhardt), OpenSees deteriorating element development and validation projects (Mahin, Moehle, Lehman), and fragility research (Project 304).

6. Plans for Year 8 if project is expected to be continued:

During Year 8 we plan to continue the project in two directions. First, we plan to interact with PEER BIP to refine the assumptions on bridge direct damage (repair costs) and indirect damage (traffic closures) related to damage to bridge components including abutments and expansion joints. Second, we plant to use a bridge testbed project to demonstrate the methodology, and allow Caltrans engineers to evaluate how realistic the results really are. Finally, we intend to put the produced DV fragility curves in a HAZUS-like setting to prepare for data exchanges within the Tri-Center Project on Geographically Distributed Systems.

7. Describe any actual instances where you are aware your results have been used in industry:

At this time, the results of this project have not been used in practice. Caltrans is continuously kept informed about the progress of this project and is providing very useful feedback.

8. Expected Milestones & Deliverables:

The milestones for this project are:

  1. Prepare a user interface enabling users who are not experts in OpenSees to create a family of script files to represent an array of typical overpass bridges and subject them to a series of earthquake time-history analyses to obtain the desired IM-EDP relations.
  2. Enable users to vary bridge parameters, such as bridge type, geometry, reinforcement and material, as well as expansion joint and abutment models.
  3. Identify already computed IM-EDP relations from a stored database and use those instead of running new analyses.
  4. Link the IM-EDP relations to IM risk information provided by other PEER projects.
  5. Link the IM-EDP relations to EDP-DM performance database provided by PEER.
  6. Provide a tool for obtaining DM fragility functions.
  7. Link DM fragility functions to direct and indirect DM-DV relations. Enable the user to specify parameters in DM-DV relations, such as the estimated cost of repair or estimated cost of traffic volume reduction.
  8. Provide a tool for obtaining data on the probability of exceeding a given level of DV value.

The deliverables of this project are:

  1. User interface software that integrates the IM-EDP-DM-DV chain for performance assessment of overpass bridges into one application.
  2. Quarterly and annual repots.
  3. Final project report.
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