Project Title/ID Number Simulation of Enhanced-Performance Post-Tensioned Bridge—5362003
Start/End Dates 10/1/03—9/30/04
Project Leader Sarah Billington (Stanford/F)
Team Members Won Lee (Stanford/GS), J. Matt Rouse (Cornell/O)

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 demonstrate how the PEER PBEE methodology can accelerate the adoption of new bridge design technologies by quantitatively assessing the performance enhancement provided by these technologies. The first detailed objective is to identify damage measures (DMs) of un-bonded post-tensioned (UBPT) bridge piers (an enhanced performance system) that relate to decision variables (DVs) relevant to bridge performance, such as safety, functionality and repair time. The second objective is to identify promising engineering demand parameters (EDPs) that can be used to characterize and quantify the appropriate DMs of un-bonded post-tensioned bridge. To relate the EDPs to the DMs, fragility functions will be developed. Due to the limited amount of experimental data available for UBPT bridge piers, the fragility information will be developed primarily analytically. Therefore, the third major objective of this project is to simulate recent cyclic and seismic experiments on UBPT bridge piers using simple macro-models as well as detailed finite element analyses. With these modeling approaches calibrated to experimental results, we will then predict the performance of alternate UBPT bridge pier designs, and thus develop fragility functions to relate various EDPs and DMs. The developed relationships will be applied to a portfolio of simple overpass structures (typical for Caltrans) to compare this enhanced performance system with traditional reinforced concrete designs.

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

Through this project, the PBEE methodology will be further developed and tested on a new structural system for structural concrete bridges, which employs post-tensioning and new materials. This research will demonstrate how the PBEE methodology can be applied to quantitatively assess the enhanced seismic performance of a new innovative bridge system and will offer a comparison of the enhanced performance system with traditional systems studied by other PEER researchers. The extent to which reductions in post-earthquake residual displacements and concrete spalling contribute to improved performance of the bridge and its role in the highway network (considering bridge functionality and restoration time as the main decision metrics) will be assessed.

This work complements the experimental and analytical work of Dr. Mahin investigating the use of UBPT systems for bridge piers and collaboration between the PI and Dr. Mahin is underway. In addition, a similar approach to developing EDP/DM relationships as that taken by PI Stojadinovic will be followed here. In this way, the enhanced performance system investigated here can be more directly compared with traditional reinforced concrete systems. It is anticipated that IM/EDP relationships for the UBPT systems will also be needed and these will be developed using the tools created by PI Stojadinovic for traditional concrete bridges as well as using analytical studies previously conducted by the PI.

3. Methodology Employed:

The enhanced performance system investigated here is that of UBPT bridge piers. This system is self-centering and provides the advantage of reduced residual displacements after a seismic event. This system can be applied to current cast-in-place construction or can incorporate many innovations for further enhanced performance. Innovations include the use of precast concrete for construction efficiency and improved concrete durability, the use of damage-tolerant fiber-reinforced concrete in hinge regions for added hysteretic energy dissipation and reduced spalling, and the use of fiber-reinforced polymer post-tensioning strand for added durability (corrosion resistance). A combination of standard and innovative versions of the UBPT bridge pier system will be investigated.

There will be two major parts to this study. In the first part, we will develop EDP/DM and begin investigating DM/DV relationships for UBPT bridge piers (full development of DM/DV relationships is proposed for Year 8). More specifically, damage measures will be identified that can be used to assess post-earthquake repair/replacement costs of a bridge using UBPT piers as well as the bridge’s post-earthquake safety and ability to function. UBPT systems are new to seismic regions and little earthquake field experience is available. Therefore these relationships will be assessed through careful study of experimental response of the system and related to damage in other concrete structures in the field, whose DM/DV relationships can be more readily assessed. With appropriate damage measures selected, promising engineering demand parameters (EDPs) that characterize and quantify the performance of UBPT bridge piers will be identified. EDP selection will be based in part on recent cyclic and seismic experiments on UBPT bridge pier systems. For example, the PI recently completed cyclic experiments on fixed-end columns and seismic experiments are underway through PEER (PI: Mahin).

To develop the EDP/DM relationship for the PBEE Methodology, fragility information will be developed analytically (note that experimental results can also be used but there are not enough to rely solely on experimental data for the fragility information). Therefore the second major aspect of this research will be to develop methods to simulate the performance of alternate designs of the UBPT system. These modeling approaches will be calibrated with recent cyclic and seismic experiments on UBPT bridge piers using models of varying complexity from simple macro-models to detailed finite element analyses. The varying levels of complexity in modeling are necessary to understand the global and local performance and to assess the ability of these models to be used as design tools in the future. OpenSees will be the initial computational platform used for the simulations. Where more detailed continuum modeling is deemed necessary (an area that OpenSees is not currently planning to pursue), the program Diana1 will be used.

1Diana is particularly powerful for detailed continuum modeling of structural concrete and includes numerous concrete models as well as embedded reinforcement, bond-slip modeling and pre-stressing. The PI has also implemented two new materials models relevant to this work in the program.

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

Our progress to date includes:

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

The PI has conducted analytical work related to UBPT bridge piers through prior research and has investigated such enhanced performance systems (that included using damage-tolerant fiber-reinforced concrete in hinge regions) through cyclic experiments and limited simulation work through an NSF Career project. While other experimental work related to UBPT bridge piers is or has been conducted in Japan (Ikeda) as well as at The University of California at San Diego (Priestley and Seible), the PI is not aware of other researchers conducting detailed simulation work related to UBPT bridge piers. Macro modeling has been conducted for other self-centering construction practices such as the hybrid frame (PRESSS System – modeling by Cheok for instance). Finally, PEER researchers Eberhard and Stanton are currently working on a project for the Washington DOT related to investigating pre-cast construction bridge decks and substructures to be used in seismic regions. This project is in the beginning stages identifying potentially promising systems for the Washington DOT.

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

We have two major goals for Year 8 project funding; extending the PEER PBEE analysis completed in Year 7 (EDP-DM relationships) to include IM-EDP and develop DM-DV relationships; and validating EDP-DM relationships with data from shake-table experiments (in collaboration with Prof. Mahin). Developing DM-DV relationships for the new systems and materials will be challenging and we will draw upon recent experiences with repair of related un-bonded post-tensioned systems as well as damage costs for bridges resulting from recent earthquakes. Detailed study of repair/replacement of other concrete bridge structures will also be conducted and related to UBPT pier systems. For the second goal, experimental shake-table data is needed in particular for incorporating damage-tolerant fiber-reinforced concrete materials into bridge piers. These materials have never been tested dynamically.

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

The PI is not aware of any direct use of her results related to seismic design in industry. However she have been discussing un-bonded post-tensioned bridge pier systems with companies such as ABAM Engineers, who are considering them in an upcoming project (to be decided in Summer 04). There has also been company interest on applications of the damage-tolerant fiber-reinforced concrete materials (e.g. LaFarge, Kuraray Co., Ltd.).

8. Expected Milestones & Deliverables:

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