CFRP Strand Application on Penobscot Narrows Cable Stayed Bridge

Rohleder, Jr., P.E., S.E., W. Jay Page 7equipment allows for the selective replacement of steel strands with <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> strands. The bridge locati<strong>on</strong> in coastalMaine provides a wide array of weather c<strong>on</strong>diti<strong>on</strong>s for a testing opportunity that includes large temperaturevariati<strong>on</strong>s and high humidity in a brackish water envir<strong>on</strong>ment. Testing of <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> strands under these actual servicec<strong>on</strong>diti<strong>on</strong>s could be accomplished with a reas<strong>on</strong>able effort that could serve as a “Living Laboratory.” Financialsupport was provided by the FHWA and the State of Maine using federal Innovative <strong>Bridge</strong> Research andDeployment program funds for the <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> applicati<strong>on</strong>s.Maine DOT with FHWA, FIGG and Lawrence Technological University collaborated to develop thedesign details for incorporating <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> strands into the bridge as special reference strands. One of the key challengeswas devising the method for anchoring these cable strands within the already designed and fabricated cable stayanchorage system for this bridge. This included developing the specific hardware for installing the strands and thentransferring the stressing force directly from the strand into the stay anchor. The design team was interested inselecting a representative number of strands to replace with <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> that would serve as a comprehensivedem<strong>on</strong>strati<strong>on</strong> at the least possible additi<strong>on</strong>al cost. Within this guideline, it was decided that we would replace tworeference strands in a short, medium and l<strong>on</strong>g stay. Variati<strong>on</strong>s in structural resp<strong>on</strong>se due to thermal effects, initialversus l<strong>on</strong>g-term bridge stresses and flexibilities in the overall bridge system would be captured by testing a shortand l<strong>on</strong>g stay with the middle stay serving as an average representati<strong>on</strong>. Additi<strong>on</strong>al selecti<strong>on</strong> criteria includedproximity to the existing data logger, utilizing stays with symmetrical strand patterns that worked best for design ofthe permanent anchor chairs, and coordinati<strong>on</strong> with c<strong>on</strong>current final stay c<strong>on</strong>structi<strong>on</strong> activities. Of the 20 possiblestays, the design team selected Stay 2 (short), 10 (average) and 17 (l<strong>on</strong>g) through the Western (observatory) Pyl<strong>on</strong>as the representative stays for carb<strong>on</strong> fiber strand installati<strong>on</strong> as shown in Figure 7. .The fast-tracked bridge c<strong>on</strong>structi<strong>on</strong> was completed with traditi<strong>on</strong>al epoxy coated steel strands installed inthe stays and the bridge opened to traffic <strong>on</strong> December 30, 2006, just 42 m<strong>on</strong>ths after identifying the need for anemergency bridge replacement. In June 2007, <strong>on</strong> the heels of a day l<strong>on</strong>g festival celebrating the bridge, six steelstrands (two each in three stays – short, medium and l<strong>on</strong>g) were removed and installati<strong>on</strong> of the <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> strandssuccessfully completed – while the bridge c<strong>on</strong>tinued to carry traffic. The <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> strands will be m<strong>on</strong>itoredindefinitely and inspected over time to evaluate the structural behavior and l<strong>on</strong>g term durability as it relates to usingthe <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> materials for many more future applicati<strong>on</strong>s in l<strong>on</strong>g span bridge designs throughout the United States.FIGURE 7 – Locati<strong>on</strong> of Stays C<strong>on</strong>taining Experimental <str<strong>on</strong>g>CFRP</str<strong>on</strong>g> <str<strong>on</strong>g>Strand</str<strong>on</strong>g>s.