Long Term Load Capacity of Epoxy and Adhesive Anchors

On July 10, 2006 a portion of the concrete ceiling in the D Street portal of the I-90 Connector Tunnel in Boston's "Big Dig" project collapsed, resulting in one fatality. In its Accident Report released July 10, 2007, the National Transportation Safety Board (NTSB) determined that the probable cause 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 loads. Over time, the epoxy deformed and fractured until several ceiling support anchors pulled free and allowed a portion of the ceiling to collapse."

USP Structural Connectors manufactures the CIA-GEL 7000 Epoxy and CIA-EA Epoxy Acrylate Anchoring Systems, neither of which were used on the Big Dig project. However, the failures in Boston have resulted in inquiries from our customers regarding the performance of the USP anchoring adhesives, especially with regard to creep resistance. All of the adhesives that USP manufactures for structural anchoring meet the industry recognized ICC ES AC58 Creep Test criteria, including the CIA-GEL 7000 and CIA-EA.

AC 58 creep testing requires that displacement measurements be taken on anchors subject to a constant load over an extended period. These displacements are recorded for a minimum of 42 days, and then projected out logarithmically to 600 days. This projected displacement is then evaluated per AC 58 requirements to determine if the adhesive is deemed acceptable for long term loading.

In addition to the results of AC 58 creep testing, USP (formerly Covert Operations) adhesives have been in service for well over a decade with an exemplary performance record, in a wide range of critical installation conditions. Finally, USP products have been tested for many other installation conditions, including:

• Dynamic/seismic loading
• Short term static loading
• Freeze thaw
• Cracked concrete
• Chemical resistance
• Elevated temperature
• Oversize holes

USP Structural Connectors anchoring adhesives have been and may continue to be used in overhead hole applications if they are properly designed and installed.

For more information, please see:
www.USPconnectors.com
www.icc-es.org
ntsb.gov