The overall goal of this study is to examine and assess various design concepts for enhancing the seismic performance of new bridge structures of the type being considered by PEER. Promising design details will be assessed though dynamic shaking table tests as well as through more extensive nonlinear dynamic analyses using the OpenSees computational platform. In particular, the potential for reducing residual displacements of bridges following severe earthquakes will be examined through the use of special plastic hinge regions containing combinations of unbonded, prestressed and mild reinforcement. Other design approaches utilizing high performance concrete, foundation details that permit rocking behavior, or other enhancements will be examined in concert with others working within the PEER Center. The PEER PBEE methodology will be utilized to quantify the benefits of these enhanced systems in comparison with conventional bridge construction in use today. The goal of this project would be to demonstrate the value of the PEER methodology for a specific application, and thereby to accelerate the adoption of new bridge design technologies into practice.

Through this project, the PBEE methodology will be further developed and tested. This research will demonstrate how the PBEE methodology can be applied to quantitatively assess the enhanced seismic performance of a new innovative bridge system. In this case the focus will be to evaluate the extent to which reductions in post-earthquake residual displacements and concrete spalling contribute to improved overall performance of the bridge.

An integrated analytical and experimental approach has been adopted. Various PEER PBEE research results related to bridge structures are being examined along with current research by the PI and other investigators worldwide to identify promising methods of enhancing bridge performance. The primary focus of these investigations will be to mitigate the substantial residual displacements that tend to occur in modern bridges when large inelastic deformations occur during severe earthquake shaking. These residual displacements have an important impact on post-earthquake operability of bridge structures, and repair costs. In addition, opportunities to work with others within PEER to explore design solutions for other behavioral aspects that adversely affect overall performance, such as spalling and foundation damage.

The initial thrust of this work will focus on shaking table testing of a lightly reinforced bridge column specimen with unbonded post-tensioning. An identical companion specimen with conventional reinforced concrete construction has already been constructed as part of another PEER project supervised by the PI. Comparison of test results for the conventional and enhanced columns with that predicted by the underlying design methodology and the OpenSees analytical platform will provide valuable data for assessing this approach.

It is planned to work closely with other investigators working on this subject to identify additional test specimens. For example, Dr. Billington is assessing DM/DV and EDP/DM relationships for bridge piers containing unbonded post-tensioned reinforcement and high performance, cement-based, ductile concrete, and Dr. Stojadinovic is carrying our extensive simulations to understand the contribution of various structural and ground motion characteristics to bridge fragilities. Drs. Martin, Kutter and Hutchinson have examined the geotechnical aspects of foundation rocking on shallow foundations. Discussions with these and other PEER investigators will help identify additional specimens. Based on current results, it is expected that two specimens would be constructed: one with a steel jacket providing confinement, and the other with improved details in the plastic hinge region (for example, using high performance concrete, unbonded mild reinforcement, modified spiral reinforcement details, etc.). It is expected that the specimens will be designed and constructed in year 6. Testing and follow-on analyses will be done in year 7.

Analytical studies will be carried out to examine and improve:

1. the ability of OpenSees to simulate observed performance, and
2. methods used for proportioning and detailing enhanced performance columns for a variety of periods and structural configurations.

The PEER PBEE methodology will be employed in these assessments.

Considerable interest has recently emerged worldwide on performance enhanced reinforced concrete bridge systems. Within PEER, this project will interface with complementary work by Drs. Billington, Stojadinovic, Eberhard, Kunnath and others related to bridge columns, Drs. Martin, Kutter, Hutchinson and others related to the effect of foundations on structural response, and Dr. Fenves and others related to OpenSees.

As indicated above, it is anticipated that two additional specimens will be constructed in the remainder of Year 6. These will be tested and analyzed in Year 7. Overall, analytical assessment of various methods to enhance the seismic performance of bridges, and to quantify this enhancement using the PEER PBEE methodology will be primarily undertaken in Year 7.

This work is just beginning. However, there is considerable interest in these techniques for important bridges where it is desired to have a bridge operable following a severe earthquake. Conventional approaches result in bridges being designed to remain essentially elastic. The enhancements considered herein pose an opportunity to improve performance and reduce costs.

Major milestones include:

1. Shaking table testing of a set of conventional and enhanced unbonded, post-tensioned columns, including brief internal summary report.
2. Analytical investigation of various methods for enhancing the performance of bridge piers.
3. Liaison with other investigators involved in the PEER program as described above to identify high-priority design concepts for subsequent assessment.
4. Design and construct two test specimens, including design-related and pretest analyses.

For year 7,

5. Shaking table testing of two specimens, including data reduction and analysis.
6. Analyses to assess ability to confirm the ability of OpenSees to predict observed response.
7. Analyses of various structural configurations and design concepts to assess the performance of these enhanced systems in terms of the PEER methodology.

Overall assessment of the enhanced bridges and conclusions related the appropriateness of these systems for implementation in practices.

In addition to a number of intermediate progress reports and documented data on the test results, a detailed report on the findings of the project will be prepared.