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Concrete In Australia : March 2008
anchors in the I-90 tunnels. Information on the long-term strength of the adhesive anchors under sustained load could not be attained by the proof-test procedure used on the anchors. Furthermore, the overhead installation of the adhesive anchors appeared to have induced voids due to poor installation technique, reducing the anchor load capacity irrespective of the creep resistance of the epoxy. The project managers and owners had failed to perform independent testing to verify load capacities provided by the epoxy supplier, or that the anchors would perform similarly in the application used. This neglected a recommendation by the American Association of State Highway and Transportation Offi cials (AASHTO) in its 2002 Standard Specifi cations for Highway Bridges, 17th Edition, that embedment anchors be subject to sacrifi cial tests at the job site to document the anchors’ capability to achieve the full tension value as shown in the manufacturer’s literature. Given the safety-critical nature of the system used it would Post accident scene with the crushed passenger car barely visible under the wreckage. The open area in the ceiling is the original location of the concrete panels. observed displacements. That we have neither of these types of testing standards in have been prudent to test a sample of the anchors to their ultimate loads. The management and design consultants should have insisted on the requirement that ultimate load tests be conducted on the adhesive anchors prior to installation, due to the potential catastrophic effects of a failure. The property of the epoxy that eventually led to the accident would not have been revealed by ultimate load tests alone. This then highlights the need for more refi ned and specifi c testing of any adhesive anchor system that is being considered for use in a sustained tensile-load application. Standards and protocols for the testing of adhesive anchors in such applications will provide designers and builders with methods designed specifically to accurately assess the long-term safety of those anchors. Site-specifi c ultimate strength values as well as the creep characteristics of the adhesive over the structure’s expected life should be considered in any standard and protocol developed. Although a lack of sustained tensile testing standards for adhesive anchors in the USA is cited, a distinction needs to be made between testing required in the product development and rating phase and that which might be employed on site to prove already installed anchors. Product rating tests (acceptance criteria) for creep performance of adhesive anchors are already in use in the USA. At the time of the Boston project the appropriate code was AC58, published by ICC- ES (International Code Council Evaluation Service). This is referred to in the NTSB report. Indeed, products which satisfy this standard are referred to, as are ones which don’t, which includes the failed adhesive in question. Unfortunately in Boston some confusion was present about exactly which type had been installed – tragically the wrong type – another contributing factor. Although there appears to be no codified sustained-load test specifi cally for on-site proving, it also appears that nobody involved even thought to suggest creep effects in the face of instantaneous site testing which didn’t explain the Australia is not necessarily a problem. In fact, there are no Australian Standards relating at all to the design or installation of post-installed anchor systems, mechanical or otherwise. However, Australia does not seem to suffer from unacceptable levels of adverse incidents. Australia has a largely self-regulated sector of the structural concrete industry where the major anchor systems suppliers opt for a high standard of applied engineering and refer as they can to AS3600 and other research and testing fi ndings. Whether for marketing advantage or for industry safety (possibly both) we all benefi t and, given that this approach is serving the industry, it would seem preferable to initiating external regulation unnecessarily. Inadequate regulatory requirements for tunnel inspections From the time the I-90 eastbound connector tunnel was fi rst opened to traffi c on January 18, 2003 until the day of collapse, inspections to determine the physical and functional condition of the ceiling system had not been performed. A comprehensive and detailed inspection manual had been provided to the owners by the management consultants. However, this manual was not used. A large number of anchors had become displaced from the tunnel roof above the suspended ceilings, which was revealed by a post accident inspection. The displacement of the hanger plates had been obvious enough that the threatened structural integrity of the ceiling system would have been shown by even a cursory inspection of the area before the accident. The anchor creep would have likely been identifi ed and preventative rectifi cation action taken, had the owners conducted inspections of the area above the suspended ceilings at regular intervals. Identifi cation of problems with some of the anchors in the tunnel occurred within weeks or months of their installation, which indicates that recently built structures are not necessarily exempt from defects. This could lead to the need for government bodies to develop and implement tunnel inspection programs to identify critical inspection elements and specify an appropriate inspection frequency. Lack of national standards for the design of tunnel finishes The outcomes of a US national survey showed adhesive Concrete in Australia Vol 34 No 1 37 PHOTO: MASSACHUSETTS STATE POLICE