United States Department of Transportation
i
Cable-Stay Strand Residual Strength Related to Security Threats
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2018-01-01
[PDF-5.62 MB]
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OCLC Number:1038072491
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Abstract:Cable-stay bridge designs are an economical bridge type for long spans. However, long-span bridges also tend to be signature spans and often serve as critical freight corridors and/or critical lifeline structures. As such, it is prudent to consider terroristic threats against these assets and strengthen cable-stay bridges to minimize vulnerabilities. The stays are a critical element in the cable-stay design that should be protected if they are easily accessible from roadways or walkways. The protection schemes applied over cable stays must be qualified based on performance criteria and judged to pass or fail based on agreed-upon acceptance criteria. This project was conducted in support of a particular bridge project where questions were raised after qualification testing regarding the acceptance criteria.
One of the criteria was 75 percent survival of wires against blast and thermal-cutting threats. After the qualification testing, it became questionable whether a wire that was gouged, nicked, or bent should be considered to have survived. The testing reported in this report assessed the residual strength of individual wires and strands in various states of damage. For blast, no correlation in strength could be identified against any of the damage metrics, though generally the entire population tested had an overall reduction in strength of 5 percent over new strands. As for the thermal cutting, gouges were quite detrimental, along with exposure to heat. The exposure to heat could easily be visually inspected based on the presence of the polyethylene coating or grease on the strands, though this was a coarse measure. A better means of assessing heat damage was through destructive hardness testing. It was found that strength did not degrade unless the strands were exposed to temperatures of more than 900 °F.
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