Research for AASHTO Standing Committee on Highways. Task 255. Development of a Test Method To Determine the Ability of Adhesive Anchors To Resist Sustained Tensile Load

On July 10, 2006, ten panels of the suspended concrete ceiling in the <st1:street w:st="on"><st1:address w:st="on">D Street</st1:address></st1:street> portal of the I-90 connector tunnel in <st1:place w:st="on"><st1:city w:st="on">Boston</st1:city></st1:place> collapsed, killing one person. The National Transportation Safety Board investigated the accident and determined that the probable cause of the collapse was the use of an epoxy anchor adhesive with poor creep resistance, that is, an epoxy formulation that was not capable of sustaining long-term tensile loads. The concrete ceiling panels were supported by a steel framework that was, in turn, supported by steel rods and turnbuckles attached to steel plates. The steel plates were affixed to the tunnel roof by stainless-steel threaded rods inserted in core holes drilled in the tunnel roof and held in place with an epoxy adhesive. Epoxy is a polymer whose stiffness is time and temperature dependent. If load is applied suddenly, it behaves like a solid, but if the load is sustained, the molecules within the polymer may begin to rearrange, causing the epoxy to gradually deform in a process called creep. Each adhesive anchor in the <st1:street w:st="on"><st1:address w:st="on">D Street</st1:address></st1:street> portal was designed to hold about 6,350 pounds. Post-accident testing showed that anchors subjected to a 4,000 pound load separated from their anchor holes in as little as 82 days. Epoxy is also used to anchor rebars; indeed, this is by the far the greatest application of epoxy adhesive in highway and bridge construction. Such applications often require the anchored rebar to be put into constant tension under structural load. Creep of epoxy-anchored rebar can compromise the integrity of structures incorporating the rebar. <st1:state w:st="on"><st1:place w:st="on">Massachusetts</st1:place></st1:state> currently prohibits all applications of epoxy anchoring adhesive, most of which involve rebar anchoring. No protocols or standards currently exist to test the ability of adhesive anchors to resist sustained tensile loads. There is a creep test protocol in the International Conference of Building Officials Acceptance Criteria 58, <em>Acceptance Criteria for Adhesive Anchors in Concrete and Masonry Elements</em>, but it is a pass-fail criteria with one load for a specific time. It does not provide any data that would predict the operational lifetime of an adhesive anchor. ASTM D 2990, <em>Standard Test Method for Tensile, Compressive, and Flexural Creep and Creep Rupture of Plastics</em>, discusses various methods for testing polymers to assess their creep behavior under sustained loads, but it does not address adhesive anchors. With no protocols or standards, public agencies are left to devise their own tests or to conduct no tests. The objective of this project is to develop a draft AASHTO standard test method to determine the ability of adhesive anchors to resist sustained tensile load. This test method will build on current methods from AASHTO, ASTM, state DOTs, and other sources and should consider (1) the creep characteristics of the adhesive over the expected life of the structure, (2) site-specific ultimate strength requirements, and (3) the effects of temperature and moisture. For purposes of this project, the term <em>adhesive anchor</em> encompasses systems for anchoring both threaded metal rod and rebar using any commercial adhesives sold for these purposes, irrespective of their specific chemical formulation.<o:p></o:p></span></p>

Language

  • English

Project

  • Status: Completed
  • Funding: $100000.00
  • Contract Numbers:

    Project 20-07, Task

  • Sponsor Organizations:

    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

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Harrigan, Edward

  • Performing Organizations:

    University of Florida, Gainesville

    219 Grinter Hall
    Gainesville, FL  United States  32611
  • Principal Investigators:

    Cook, Ronald

  • Start Date: 20080313
  • Expected Completion Date: 0
  • Actual Completion Date: 20090531
  • Source Data: RiP Project 17223

Subject/Index Terms

Filing Info

  • Accession Number: 01464530
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 20-07, Task
  • Files: TRB, RiP, USDOT
  • Created Date: Jan 3 2013 2:44PM