Pile Bent Design Criteria

This study was undertaken to review the design of pile bents by the North Carolina Department of Transportation (NCDOT). Research was performed to investigate current design methodologies and compare practice approach to other feasible and cost effective design methods. As such, two goals were pursued: i) enhancing the current equivalent frame model of the pile bents such that it fully considers the resistance of the soil around the piles, and, ii) adopting a comprehensive state of practice, which involves the integration of a comprehensive software and analytical solutions. It was also deemed important to study displacement limits imposed on bridge design and suggest improved limits based on the results from the soil/structural models. To achieve the study objectives, four bridge case studies provided by the NCDOT were modeled. The 3-D finite element modeling utilized two software packages: MultiPier and SAP 2000. MultiPier was used as a tool to specifically analyze piles and bridge bents. SAP2000 was used to verify the MultiPier model, and as a tool to evaluate proposed equivalent frame models. Results indicated that MultiPier is the most promising program, considering future NCDOT applications. This is mostly due to the built-in soil models and packaged features that include AASHTO load cases and load resistance factors modules. If, however, MultiPier is to be used as a design tool, some preprocessing would be needed to determine live loads. Postprocessors are also required for design of bent cap section reinforcement. The results from the 3-D verification analyses performed in SAP showed good agreement with the MultiPier results. Bridge models built to optimize the design (that is, to reduce the size of or number of the piles used as well as the cap section’s rebar and size) showed that cost savings may be realized using the nonlinear analysis approach. In order to achieve the objective of enhancing the current equivalent frame models, a method is proposed to calculate a Point of Fixity (POF) and equivalent frame height to better estimate moments, shears and displacements in bridge substructures. Based on this model, it is shown that NCDOT's current definition of POF is conservative. The proposed model yields results that are closer to results from nonlinear numerical analysis. Geotechnical and structural displacement limit states were investigated but it is clear that there is a lack in literature of well-defined limit states for both the super and sub structures. Preliminary limit state models are proposed to investigate allowable displacements due to opening of a gap between soil and pile and closing of expansion joints.

Language

  • English

Media Info

  • Media Type: Web
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 144p

Subject/Index Terms

Filing Info

  • Accession Number: 01099457
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/NC/2006-14, Research Project 2005-19
  • Files: TRIS, USDOT, STATEDOT
  • Created Date: May 6 2008 1:04PM