Thrust Area II – Bridges and Transportation Systems


The Bridges and Transportation Systems research program is directed toward further developing the performance-based earthquake engineering (PBEE) methodology developed by PEER, and demonstrating its utility through application to difficult bridge design problems that integrate structural and geotechnical considerations. Previous proof-of-concept testbed projects (Humboldt Bay and I-880) demonstrated the application of the PBEE methodology to two very complicated large bridge structures. The results were well received by business and industry representatives, but it was noted that the utility of the methodology now depended on further development and implementation in simpler and more transparent procedures. This effort would require further clarification of the procedures and methodologies used to derive the various components of the methodology (e.g., fragility curves, damage measures, decision variables). Accordingly, the goals for the Bridges and Transportation Systems research program are to: (1) further develop the PBEE methodology and package it in ways that are accessible to the engineering community, (2) demonstrate the PBEE methodology by applying it to more common bridge configurations, including cases involving the use of performance-enhanced columns and cases involving liquefaction and lateral spreading hazards, (3) address the knowledge base and enabling technology needs for the above demonstration problems, and (4) advance our capabilities to model seismic risk for transportation and geographically distributed systems.

Strategic Plan

The strategic plan for TA II, as depicted in Figure 2.15, defines a coordinated sequence of research projects over Years 8–10 to achieve the goals described above. The strategic plans for the current Year 9 and the following Year 10 are largely unchanged from the plans that were originally developed in Year 8 except for a few project changes that were made in response to Year 8 findings and progress and a new application study initiative. There are four application testbed projects that are demonstrating the PBEE methodology for variations from a common baseline bridge structure (Stojadinovic´ 2442004, Mahin 2402004, Kramer/Arduino 2412004, Bray 2422004/Martin 2432004). The variations that each testbed project is addressing will exercise the methodology for very different purposes, thereby illustrating its usefulness in different ways. The researchers for these projects are working closely together, sharing components and models, and bringing different technical expertise to the group effort.

This group effort includes a lead project on clarifying, simplifying, and communicating the PEER methodology that included a detailed report in Year 8 that clearly specified recommended procedures for implementation of the PEER methodology for bridge systems (Stojadinovic´ 2442004). The draft of this detailed report provided a synthesis of best practices that the other projects are utilizing and building upon. This lead effort on the methodology is continuing its complete demonstration for a baseline bridge structure (Stojadinovic´ 2442004) that was selected with input from our BIP representatives (Ketchum 2522004). The baseline bridge configuration is a five-span bridge with earthen abutments and typical Caltrans detailing. By focusing on a prototypical baseline bridge, this project is providing a complete demonstration of the PEER methodology in advance of the other parallel testbed projects, and therefore providing the framework for them to utilize and build upon.

The benefits of performance-enhanced piers are being evaluated using PEER methodology (Mahin 2402004), thereby illustrating both the utility of the performance-enhanced piers and the utility of the PEER methodology for evaluating new technologies. This project builds upon the experimental and computation efforts on performance-enhanced piers, as described later. In addition, this project will address the impacts of near-field motions.

Strategic plan: Thrust area II — Bridge and transportation systems

The effects of liquefaction and lateral spreading on bridges are being evaluated through two parallel testbed projects. The first project (Kramer/Arduino 2412004) is utilizing continuum soil modeling capabilities in OpenSees as part of the numerical model of the prototype bridge system. This project is providing additional insights into the physical effects of liquefaction of bridge performance through the numerical modeling, and also demonstrating how to effectively utilize the PEER methodology in making informed decisions as to whether remediation is warranted or not.

The second testbed project regarding liquefaction effects on bridges (Bray 2422004/Martin 2432004) includes the evaluation of simplified design recommendations and procedures, and is expected to evaluate alternative remediation schemes. This project will translate various PEER research findings into forms that are quickly adopted in design practice, and thus fill an urgent need for Caltrans and industry. In addition, this project will demonstrate how the PEER methodology can be effectively used with simpler design-level analysis methods to make informed decisions.

Fragility curves that relate damage measures to engineering demand parameters and decision metrics are being further developed for a broader range of structural components, as needed for the bridge testbed projects (Eberhard 2452004). Fragility curves for implementation in transportation systems analyses will also be further developed (Stojadinovic´ 2442004, Brandenberg 2572005).

Research on cumulative damage associated with low-cycle fatigue buckling and fracture of longitudinal reinforcement will continue (Lehman 2472004). This cumulative damage research includes testing and model development (Lehman 2472004) and computational implementations in TA IV (Kunnath 4232004).

The innovative idea of enhancing the performance of bridge piers by applying vertical post- tensioning is being further developed through experimental and analytical studies (Mahin 2402004, Billington 2462004). These studies are motivated by the observation that post- earthquake residual displacements are one of the primary contributors to bridge closure and replacement. The objective of the investigations is to show how post-tensioning, combined with mild steel reinforcement, can reduce residual drifts. The results of these studies will be fed into the testbed project, wherein the utility of PEER methodology to evaluate new technologies will be demonstrated.

Experimental and computational studies of soil-foundation-structure interaction will continue for pile foundations in liquefying and laterally spreading ground (Boulanger 2392004, Kramer/Arduino 2412004). Dynamic centrifuge model tests are being performed for pile supported abutments embedded in a laterally spreading soil profile (Boulanger 3F03 in TA III). These centrifuge tests are focused on evaluating the restraining effect of piles on abutment deformations, which is an important mechanism upon which designers are increasingly beginning to rely. Numerical analyses of these and other centrifuge data are contributing to calibration of OpenSees models and simpler design analysis models. These studies continue PEER efforts in advancing this field through parallel experimental, computational, and performance-based design projects.

The modeling of earthen abutments in seismic analyses of bridges is being evaluated (Ashford 2552005) in conjunction with some large-scale testing funded separately by Caltrans. This project is providing essential support for the testbed application studies.

Continuing advances in OpenSees capabilities will also support the bridge systems thrust area. Specifically, the advances in computational capabilities will be exercised by performing three dimensional modeling of soil-pile interaction in liquefied ground (Elgamal 4242004), for which the ability to do coupled modeling in OpenSees is essential (Jeremic´ 4262004).

Research on transportation systems is progressing in several ways. Decision variables for individual bridges are being developed that account for the influence that the bridge has on the transportation network (Kiremidjian 2562005). A companion project (Fan 2502004) is addressing two related problems: (1) from a transportation operational viewpoint, how to route traffic through damaged transportation networks so that emergency response tasks can be carried out effectively; and (2) from a disaster management and mitigation viewpoint, how to develop and support effective strategies for recovering and retrofitting transportation systems to ensure reliable movement of emergency vehicles and to minimize the total societal disruption. A third project was initialized to provide improved fragility relations for bridges founded in liquefiable deposits (Brandenberg 2572005) for use in the transportation network analyses (Kiremidjian 2562005). The above projects have required close collaboration and exchanges of data, algorithms, and findings, and have involved collaborations across centers and industry (Stu Werner; Caltrans). These efforts all contribute directly to Tri-Center collaborations (Moehle 2532004).

Critical Mass and Level of Effort

The strategic plan brings together PEER researchers with the appropriate critical mass and expertise to achieve the goals for the Bridge and Transportation Systems thrust area. The four bridge application (testbed) projects bring together six researchers (Stojadinovic´ 24492004, Mahin 24022004, Kramer/Arduino 2412004, Bray 2422004, Martin 2432004) with complementary skills, such that their close coordination and collaboration provide opportunities for more rapid advancements in the PBEE methodology and its packaging for the engineering community. The other projects provide support for the testbed projects by addressing key knowledge base needs and by enabling technology needs. For performance-enhanced columns, the supporting projects include experimental and computational efforts by Mahin (2402004), Billington (2462004), and Lehman (2472004). The role of the earthen abutments is being addressed by Ashford (2552005), while the effects of liquefaction are being supported by Boulanger (2382004). In addition, the bridge testbed project involving liquefaction effects will leverage past accomplishments by PEER researchers and their close connections with major efforts at MCEER and in Japan. Several OpenSees efforts will address needs for this thrust area (e.g., Elgamal 4242004, Jeremic´ 4262004, Kunnath 4232004). The work on EDP-DM-DVs by Eberhard (2452004), bridge fragilities (Stojadinovic´ 2442004), and abutment modeling (Ashford 2552005) provide support across all bridge testbed projects, and the work by Fan (2502004), Kiremidjian (2562005), Brandenberg (2572005), and Moehle (2532004) contribute to transportation systems and the Tri-Center initiative. All projects will benefit from close communications with practitioners and Caltrans.

Research Advances and Deliverables

The four testbed application projects have made significant advances toward demonstrating the application of the PBEE methodology in the various ways intended. The methodology has been advanced and the expected performance of the prototypical Caltrans five-span bridge has been benchmarked. The two projects involving liquefaction effects have advanced the utilization of OpenSees as a modeling tool, while simultaneously advancing our ability to effectively apply the PBEE methodology with either advanced or simplified analysis procedures to bridges in areas of liquefaction.

Significant advances continue to be made regarding the seismic performance of pile foundations in liquefied ground, with contributions coming from researchers across thrust areas II, III, and IV (TA II testbed teams, Boulanger, Ashford, Conte, Elgamal, Jeremic´). Contributions have included original experimental data, identification of fundamental mechanisms of interaction, development of computational modeling tools, and guidance on simplified design methodologies. Many of these contributions are included in the proceedings of the March 2005 workshop held at UC Davis (Boulanger 2372003). This workshop brought together engineering practitioners and researchers from across the U.S. and internationally to summarize the most current understanding of fundamental mechanisms, numerical modeling abilities, and design recommendations for practice. The proceedings were published as an ASCE Geotechnical Special Publication.

Advances have been made experimentally and computationally in performance-enhanced columns (Mahin and Billington) and cumulative damage in reinforcing bars (Lehman). Damage models and decision models have been advanced, including an electronic online database of column tests and fragility relationships between EDPs (such as column ductility ratios, plastic hinge rotations, and strains) and damage states (Eberhard) and the translation of field damage observations into decision making for bridges (Porter).

The Tri-Center initiative has advanced the network modeling of transportation and distributed network systems (Kiremidjian, Fan, Moehle) and identified key areas where improved fragility relations and inventory knowledge is needed.

Future Plans

The future plans for the Bridges and Transportation Systems Thrust Area follow from the previously established plan for Years 8–10. The project by Fan was expanded to cover the issues that were important to the collaboration with Kiremidjian. The project by Brandenberg was recently added to ensure the timely provision of fragility relations to Kiremidjian's and Fan's network models. Ashford's project was re-directed toward providing more support regarding the behavior of earthen embankments, which had become an urgent need in the testbed projects. A couple of other projects may warrant redirection based upon progress in Year 9, but for the most part it is expected that the testbed and supporting projects will require extensions through Year 10 (as tailored to specific project needs). The success of these testbed studies will show that the PBEE methodology can be used to assess existing bridge design procedures, assess new performance enhancing technologies, and assess challenging geotechnical hazards like liquefaction.

Funds have been allocated for a new Year 10 initiative (2582006) that will further explore PBEE applications to bridges and lifeline systems. A major portion of this effort will be directed toward a study to evaluate the implications of a large earthquake on the Hayward fault in the San Francisco Bay Area. This scenario study will leverage ongoing efforts of the transportation network study to examine damage to buildings, bridges, lifeline systems, and their inter- connections. The value of an earthquake scenario in attracting the interest of government agencies, facility owners, and the public was demonstrated with a recently completed scenario study of a repeat of the 1906 earthquake on the San Andreas fault. The proposed study will be an effective vehicle for integrating PEER’s research projects in ground motions, simulation of geotechnical and structural systems, and loss modeling. This, along with the other bridge testbed application studies, will exercise the PBEE methodology in ways that are accessible to the engineering community and will provide opportunities for post–Year 10 efforts on utilizing the PBEE methodology for other classes of bridge structures, other technologies, and other hazards.


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For additional details, see the PEER Annual Report - Volume 2 (PDF file - 7.6 MB).