Benchmarking Enhanced Performance of Post-Tensioned RC Piers with Ductile Materials - 2462005

Project Title—ID Number	Benchmarking Enhanced Performance of Post-Tensioned RC Piers with Ductile Materials - 2462005
Start/End Dates	10/1/05 – 9/30/06
Funding Source	PEER-NSF
Project Leader (boldface) and Other Team Members	Sarah Billington (Stanford/F), Won Lee (Stanford /GS), PEER Summer Intern (Stanford /US)

Project goals and 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. We will be demonstrating the application of the PBEE methodology while also identifying where in the process the uncertainties have the most impact on the final assessment. The demonstration will be performed on a baseline bridge also studied by other researchers in PEER's Thrust 2 area, to facilitate comparisons of performance assessment. The technologies investigated here apply to the design of bridge piers and will focus on unbonded vertical post-tensioning for self-centering, segmentally precast concrete, and high performance fiber-reinforced concrete materials for localized regions of a structure. IM-EDP and EDP-DM relationships will be developed analytically using a combination of OpenSees modeling and where necessary, more advanced finite element (continuum) modeling. All models have been or are being calibrated again recent cyclic and seismic experiments on reinforced concrete and enhanced-performance bridge piers.

Role of this project in supporting PEER's mission (vision)

Through this project, we are demonstrating how the PEER PBEE methodology can be applied to assess quantitatively new structural systems for structural concrete bridges, which employ post- tensioning, jacketing techniques and the application of new high-performance materials in localized regions. This research will offer a comparison of enhanced performance systems with traditional systems studied by our group as well as other PEER researchers who are using different techniques for various steps in the PBEE framework. The extent to which reductions in post-earthquake residual displacements, concrete spalling, and bar buckling contribute to improved performance of the bridge and its role in the highway network (considering for example bridge functionality, repair cost and restoration time as decision metrics) are being assessed

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Methodology employed

The enhanced performance system investigated here is that of unbonded post-tensioned (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 steel jackets for added confinement, damage-tolerant fiber- reinforced concrete in hinge regions for added hysteretic energy dissipation and reduced spalling. The use UPBT in bridge piers is being conducted first and compared with traditional systems. Innovative versions of the UBPT bridge pier system will then be investigated.

To demonstrate the application of the PEER PBEE Methodology to the assessment of new technologies, we are developing IM-EDP-DM-DV relationships for a baseline bridge that is being studied by several researchers in Thrust Area 2. For the systems utilizing the ductile fiber- reinforced concrete materials, the EDP-DM relationships are being developed analytically, as there is not enough experimental data on the enhanced performance systems to create experimentally-based fragility relationships. The experimentally-based fragility relationships developed by PI Eberhard are being used for the EDP-DM relationships for the traditional concrete and the UBPT piers that do not incorporate ductile fiber-reinforced concrete. All analytical models being developed to complete these analyses are being calibrated with available cyclic and seismic data for UBPT bridge pier experiments. In some cases, modifications to models for traditional bridge piers are being made (e.g. modification of a concrete model to capture residual displacements). Additional or more detailed model development from other Thrust 2 researchers is underway and will be incorporated into our analyses as recommendations are available. The IM-EDP relationships are being developed using incremental dynamic analyses. Modeling uncertainty will be incorporated using the FOSM method. Fragility curves representing the EDP-DM relationships are being developed using finite element analyses in conjunction with reliability methods.

DM-DV relationships have estimated using HAZUS for a relative comparison between traditional reinforced concrete piers and UBPT piers. Consultation with maintenance engineers at Caltrans and cost estimators being carried out by PEER collaborators will be used to improve the accuracy of absolute values used in the DM-DV relationships.

With a heavy reliance on simulation to assess enhanced performance bridge piers, model calibration and validation against experiments is essential. As stated above, the modeling approaches used here continue to be calibrated with recent cyclic and seismic experiments on UBPT bridge piers, structural elements using damage-tolerant fiber-reinforced concrete and traditional reinforced concrete (for capturing residual displacements). Models for of varying complexity from simple macro-models to detailed finite element analyses are being used. 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. Furthermore, several simple experiments are being designed in collaboration with PI Mahin to investigate design details, materials and construction methods for enhanced performance piers using ductile fiber reinforced concrete. The purpose of the experiments is to serve as pilot studies for a larger- scale shake table test in the future.

Brief Description of previous year's achievements, with emphasis on accomplishments during last year (Year 8)

We developed a model of a UBPT bridge pier for the baseline bridge and used it to analyze the bridge in comparison with a traditional bridge. We completed a demonstration of the framing equation (the four steps from IM to DV) for traditional bridge piers and UBPT using several simplified models (e.g. HAZUS data for DM-DV). It was found that at hazard levels above a 2% in 50 year hazard, the UBPT columns displayed excellent behavior, with peak drifts similar to those of the RC columns but with significantly reduced residual displacements (roughly 35% of those of RC columns). Furthermore the anticipated downtime for a bridge with a UBPT pier was less than 1 day whereas for the bridge with an RC column, the downtime would be 29 days. At hazard levels of 2%, 10% and 50% in 50 years, the UBPT and traditional RC piers are expected to behave similarly according to the PBEE analyses.

During the summer, PI Mahin and PI Billington each had a PEER REU student and together they worked on setting up experiments to record the stress-strain response of confined ductile fiber- reinforced concrete.

Other similar work being conducted within and outside PEER and how this project differs

Within PEER, a similar step-by-step approach for demonstrating the PBEE methodology has been carried out by PI Stojadinovic for a traditional reinforced concrete highway bridge. We will compare our results for a traditional bridge with theirs as we performed some of the steps using different methods (e.g. IDA for the IM-EDP step vs. the “cloud” approach). PI Mahin is also investigating enhanced performance bridge piers with an emphasis on experimental studies, offering further opportunities for collaboration. We collaborated on simple material tests of ductile fiber-reinforced concrete over the summer (see section 4) and collaboration on the application of this material to enhanced-performance bridge piers is continuing in Year 9.

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 some 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) and the University of Nevada at Reno (Saiidi and Sanders), 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 precast construction for bridge decks and substructures to be used in seismic regions. A goal of this project is to identify potentially promising precast systems for the Washington DOT.

Describe any instances where you are aware that 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 Caltrans has recently called for proposals to investigate the development of a segmentally precast bridge pier system that could be a direct competitor to traditional reinforced concrete in seismic regions. This is the exact topic of the PIs previous research for non-seismic regions as well as more recent research on segmentally precast bridge piers for seismic regions using UBPT. Additionally, there has also been company interest on applications of the damage- tolerant fiber-reinforced concrete materials (e.g. LaFarge, Kuraray Co., Ltd.).

Expected milestones & deliverables

A comparison of a variety of enhanced-performance systems to a traditional system using the baseline bridge adopted by Thrust Area 2 will be conducted. This will include several refinements to the analyses performed in Year 8. This comparison will cover the entire PEER PBEE Methodology. Analysis will also be conducted on the effect of using differing approaches in the various steps of the PBEE Methodology. Finally, a constitutive model to capture residual displacements in concrete (currently not possible in OpenSees) and one to capture the tensile strain-hardening and unique reversed cyclic loading response of ductile fiber-reinforced concrete will be created and validated for use in OpenSees.

Member company benefits

A complete demonstration of the application of PEER-PBEE for the systematic assessment of a new technology and new materials for highway bridge design.