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 the damage measures (DMs) of unbonded 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. Promising engineering demand parameters (EDPs) that characterize and quantify the appropriate DMs of unbonded post-tensioned bridge piers will then be identified. The second objective is to simulate recent cyclic and seismic experiments on UBPT bridge piers using detailed finite element analyses as well as simple macro-models with the goal of modeling and predicting accurately various EDPs.
This project provides a new structural system using new materials with which to test the PEER PBEE methodology. The ability of the PEER PBEE methodology to accelerate the adoption of new technologies will be assessed in general. This project also supports the bridge testbed activities (in particular the I-880 testbed) as well as the development and assessment of computational models in OpenSees.
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 highly ductile 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 are two major parts to this study. In the first part, we are identifying damage measures for UBPT bridge piers that can be used to assess post-earthquake repair/replacement costs of a bridge using this system 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 are more easily determined. Detailed study of repair/replacement of bridge structures will also be conducted and related to UBPT pier systems. With appropriate damage measures selected, promising engineering demand parameters (EDPs) that characterize and quantify the performance of unbonded post-tensioned bridge piers will then be identified. EDP selection will be based on recent cyclic and seismic experiments on UBPT bridge pier systems. For example, cyclic experiments on fixed-end columns were recently completed by the PI (Fig. 1) and seismic experiments are underway through PEER (PI: Mahin).
In the second part of this study we will develop methods to simulate recent cyclic and seismic experiments on UBPT bridge piers using models of varying complexity from simple macro-models to detailed finite element analyses. The goal of the simulation work is to develop methods of modeling and predicting accurately various EDPs. 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 main computational platform. Where more detailed continuum modeling is deemed necessary (an area that OpenSees is not currently planning to pursue), the commercial program DIANA* will be used.
* DIANA is particularly powerful for detailed continuum modeling of structural concrete and the PI has implemented in it two new materials models relevant to this work.
In related work, the PI recently completed a series of large-scale cyclic tests at Cornell University on precast segmental concrete bridge piers using unbonded post-tensioning and in some cases highly ductile fiber-reinforced concrete. These columns are, to the PI’s knowledge, the first of this system using high-performance materials to be tested in reverse curvature. In Year 6, detailed study of the performance of these columns at various stages of loading and deformation will be assessed along with other experiments on similar systems currently underway. Detailed assessment of experimental results will aid in the identification of DM/DV and EDP/DM relationships (see Milestones).
The PI has conducted analytical work related to UBPT bridge piers through prior research at Cornell University and has investigated such enhanced performance systems (that included using highly ductile fiber-reinforced concrete in hinge regions) through cyclic experiments and limited simulation work through an NSF Career project. The proposed PEER work focuses on finding methods to simulate these and other experiments using detailed and macro-models. 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 and precast walls (PRESSS Systems).
Year 7 will focus on the continued development of simulation approaches with further calibration of the models to more recent experiments (including those through PEER in Year 6). The application of the PEER PBEE Methodology to an alternate design for the I-880 testbed using the enhanced performance system and results from Year 6 will be carried out. In addition, collaboration with PEER researcher Mahin will be furthered for the analysis and development of the PBEE Methodology for enhanced-performances systems.
- DM/DV and EDP/DM relationships for unbonded pot-tensioned bridge piers (including precast systems and systems that use high performance ductile cement-based materials)
- Calibrated modeling approaches to simulate the cyclic and seismic performance of unbonded post-tensioned bridge piers. Modeling approaches will be through OpenSees and in the case of detailed continuum models not available in OpenSees, with the finite element code DIANA.
- Sets of DM/DV and EDP/DM relationships for structural concrete bridge piers using unbonded post-tensioning and new materials.
- A report on modeling approaches to predict and assess the performance of structural concrete piers that use unbonded post-tensioning and new materials.