Link to Latest Report: June 2019 Progress Report
In seismic design of transportation structures there are several competing demands that must be met: high strength and stiffness, large ductility, damage resistance and efficient construction. Prior research at the UW demonstrates that concrete-filled tubes (CFTs) can meet these competing demands. For a given diameter, CFTs have larger strength and stiffness than an RC component. Testing of CFT connections demonstrates their ductility, with drift capacities larger than 8%. When used with precast components, CFTs facilitates ABC.
This research builds on the prior CFT research to develop connections specific for use in structural systems for high-speed rail (HSR). While the FIU study focuses on the column-to-cap connection, this study will investigate a new, untested direct column-to-pile connection. This connection is critical to the structural performance and cost of the system, but few studies have focused on it, in particular for ABC. This study will advance design and construction of pile connections for HSR.
The research will investigate the connection and HSR system response using advanced, nonlinear analysis methods. A thorough literature review will identify types of connections and document their structural response; the UW team will work with the HSR team to identify one or more connections for further study. Using high-resolution finite element modeling, salient parameters of selected connections, including materials, geometry, and soil-structure interaction, will be studied. Those results will be used to develop spring and line-element nonlinear models of the components and connections as a function of the important connection parameters. The final research task will investigate the seismic response of a prototype HSR CFT system using these nonlinear models. Connection design details, seismic performance objectives, seismic hazard levels, and soils will be varied to study their impact. The results will provide important initial guidelines for the connection design and seismic performance which will found a future experimental research study to validate the work
The overall goals of the proposed research are to investigate CFT connections and other column-to-pile connections including the seismic response and resilience, including damage, of selected CFT connections using high-resolution finite element analyses. Longer term work (beyond Cycle 1) will focus on investigation of a high-speed rail (HSR) system for study (to be selected in collaboration with the CA HSR technical team) through a limited structural analysis simulation using line-element nonlinear modeling methods to investigate the impact of salient parameters on the response including (1) connection type, (2) soil structure interaction and (3) seismic hazard level
The following research tasks are proposed to achieve these objectives.
Task 1 – Literature Review and Agency Discussions.
A comprehensive review of past experimental research will be completed. Experimental results evaluating resistance, stiffness, and force-deflection of direct column-to-pile connections will be studied. This task is expected to be completed quickly, because the researchers are familiar with most of the past work through research performance on other CFT research projects funded by Caltrans and WSDOT.
Task 2 –Collaboration and meeting(s) with CAHSR.
The UW research team will meet with the CAHSR technical team with the objectives of (1) understanding the design objectives for the column-to-pile connection, (2) investigating what agencies in other parts of the world have done in developing High Speed Rail, and (3) identifying a possible system for further investigation though nonlinear analyses.
Task 3 – Investigation of Design Parameters though Finite Element Analysis
The analytical program will (1) simulate the bond condition of a straight-seam tube and (2) investigate spacing and geometry of the interior rings proposed to provide mechanical bond. Bond stress is viewed as a critical parameter in the analysis. The CFST composed of a straight-seam tube and concrete without a low-shrinkage admixture (No LSA), had very little bond capacity in comparison with the other CFST specimens.
Task 4 – Performance Evaluation of System ~ (Future Research)
Working with the CAHSR team, the UW team will identify an HSR system for structural investigation using nonlinear analysis methods. It is expected that a zero-length, fiber-section element will be used to simulate the connection(s), while distributed plasticity elements will be used to model the columns and piles; this approach will be calibrated using the results from Task 3. However, it is not possible to fully develop design guidelines for the connection without experimental results (this experimental program is proposed as a future task collaborative with WSDOT). It is expected that a limited study will be conducted with the primary variable soil-structure interaction.
Task 5 – Final Report
A Final Report will be written that summarizes the methods used and the findings reached during the project. Detailed information about and results from the analyses conducted in Tasks 3 and 4 will be summarized in the analyses. The report will also present future research studies to further investigate the connections experimentally; the experimental results are required to fully develop design expressions for the connections.
Dr. Dawn Lehman and Dr. Charles Roeder
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