Proposed AASHTO Specifications for Design of Piles for Downdrag

The AASHTO LRFD [Load and Resistance Factor Design] Bridge Design Specifications (BDS) recognizes that piles in settling soil experience downdrag forces from negative skin friction and may also move downward with the adjacent soil. Many bridges are constructed in areas where there is compressible soil or liquefiable soil, which necessitates the con- sideration of downdrag forces and associated settlement. Downdrag for static and seismic conditions has increasingly placed greater demands on existing and new foundations and also led to higher construction costs. Therefore, there was an immediate need to review the fundamental behavior of piles subject to downdrag and propose design requirements for the implementation of the neutral plane method for the evaluation of downdrag and the static and seismic design of piles. Under NCHRP Project 12-116A, "Proposed AASHTO Specifications for Design of Piles for Downdrag"; the University of Arkansas was asked to (1) propose modifications to the bridge design requirements for the static and seismic design of piles for downdrag and (2) develop design examples to demonstrate the application of the proposed design require- ments. The research team proposed draft language for consideration by AASHTO in the next update of the LRFD BDS and provided analysis and design examples to illustrate the proposed updates. NCHRP Research Report 1112: Design of Piles for Downdrag presents procedures for determining downdrag loads used in the design of bridge piles. The procedures were developed based on an extensive review of the state of practice and a collection of existing field test data. The research findings will be used by geotechnical engineers responsible for designing bridge foundations for state departments of transportation. In addition to this report, NCHRP Web-Only Document 398: Pile Design for Downdrag: Examples and Supporting Material is available on the National Academies Press website (nap.nationalacademies.org) by searching for NCHRP Web-Only Document 398.

• Record URL:
  http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4919
• Supplemental Notes:
  • The final deliverables will be published as NCHRP Research Report 1112 and NCHRP Web-Only Document 398.

Language

• English

Project

• Funding: $420000
• Contract Numbers:

  Project 12-116A

• Sponsor Organizations:

  National Cooperative Highway Research Program

  Transportation Research Board
  500 Fifth Street, NW
  Washington, DC  United States  20001

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590

  American Association of State Highway and Transportation Officials (AASHTO)

  444 North Capitol Street, NW
  Washington, DC  United States  20001
• Project Managers:

  Abu-Hawash, Ahmad

• Performing Organizations:

  University of Arkansas, Fayetteville

  Fayetteville, AR  United States 
• Principal Investigators:

  Coffman, Richard

• Start Date: 20201015
• Expected Completion Date: 20240229
• Actual Completion Date: 20240229

Subject/Index Terms

• TRT Terms: Bridge design; Drag forces; Earthquake resistant design; Load and resistance factor design; Specifications; Support piles
• Identifier Terms: AASHTO LRFD Bridge Design Specifications
• Subject Areas: Bridges and other structures; Design; Highways;

Filing Info

• Accession Number: 01730001
• Record Type: Research project
• Source Agency: Transportation Research Board
• Contract Numbers: Project 12-116A
• Files: TRB, RIP
• Created Date: Feb 3 2020 7:57PM