Project Title/ID Number Test of Enhanced Performance Post Tensioned Columns—5342003
Start/End Dates 10/1/03—9/30/04
Project Leader Stephen Mahin (UCB/F)
Team Members Junichi Sakai (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 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 un-bonded, pre-stressed 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.

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

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.

3. Methodology Employed:

figure 1
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.

figure 2

The initial thrust of this work has been focused on shaking table testing of a lightly reinforced bridge column specimen with un-bonded post-tensioning. The supervising PI has constructed an identical companion specimen with conventional reinforced concrete construction as part of YR 6 PEER project. 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 un-bonded 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, un-bonded mild reinforcement, modified spiral reinforcement details, etc.). It is expected that the specimens will be designed and constructed in year 7. Testing and follow-on analyses will be done in year 7 and 8.

Analytical studies have been 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.

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

An extensive parametric analytical investigation has been completed. Several papers and a report have been published on this work. The test specimen noted above has been constructed and is awaiting testing. Several designs have been completed for possible tests in the next phase of testing.

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

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.

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

More complex systems will be tested and analyzed, such as a multiple column specimen with plastic hinging at the top and bottom of the columns. Particular focus will be on improving the detailing (steel jacketing, high performance concrete, de-bonding of mild reinforcement in the plastic hinge regions) and the impact of this on damage measures.

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

There is considerable interest in Caltrans and elsewhere in the concepts being introduced here. More research needs to be done to validate the approach prior to implementation.

8. Expected Milestones & Deliverables:

Testing of first specimen, construction of second specimen, analysis of experimental results. Several presentations are planned and a report on the experimental and analytical results will be prepared.

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