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This report is an archived publication and may contain dated technical, contact, and link information
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Publication Number:  FHWA-HRT-17-109    Date:  January 2018
Publication Number: FHWA-HRT-17-109
Date: January 2018


Cable-Stay Strand Residual Strength Related to Security Threats

Conclusions and Recommendations

This project was undertaken strictly to answer questions pertaining to qualification of cable-stay bundle protection measures and the acceptance criteria used. The specific question addressed was, What residual strength exists for individual strands with all wires intact (not severed) or with only one wire intact to various types of damage? This focus for the testing means the conclusions are only applicable to the qualification tests performed to enable evaluators or quality inspectors to evaluate the satisfactory acceptance of a protection system against prescribed hazards identified from an ATVA. The results were not acquired for the purpose of assessing or load rating entire cable-stay bundles that may be damaged from a hazard event on a real bridge. The following conclusions were derived from the results of this project:


Future blast qualification testing of cable bundles should abandon careful inspection of individual strands for curvature, birdcaging, and impacts. Rather, it is recommended that damage from all these forms of deformation be lumped together into an overall reduction factor applied to all surviving wires and that acceptance inspection only require counting the number of surviving wires. A reduction factor of 0.95 is recommended to be multiplied against the number of wires surviving the test to define the number of wires then compared to the acceptance criteria. This overall reduction factor accounts for the small reduction in the strength of FBC and IBC strands and the larger reduction in the strength of strands with six wires cut.

The PTI DC-45 committee should consider adding in qualification criteria for security threats to their DC45.1 specification to help unify this type of testing across the country.(5) Right now, their acceptance testing only considers corrosion resistance, anchorage fatigue, and fire resistance. As far as this work is concerned, only blast and thermal-cutting events can be addressed, and recommendations can be made only for acceptance criteria to qualify hardening systems for cable-stay bundles. The conclusions within this report regarding a mean blast bundle reduction factor and hardness limits for thermal threats are only considered starting points for deliberation.

Future Work

Working toward a national standard for qualification of hardening systems for cable-stay bundles, the following two topic areas are identified as deserving of future work:

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