Frequency response of damage [sic] external post-tensioned tendons

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Title: Frequency response of damage [sic] external post-tensioned tendons
Author: McKinstry, Christopher Archer
Abstract: Bridges with external post -tensioned tendons are considered to be more durable than bridges with internal tendons (tendons within the webs and flanges ) , because external tendons are easier to inspect . In addition , in the event that extensive corrosion damage is detected , it is possible to replace an external tendon . However , an appropriate inspection for detecting damage needs to be determined for external tendons . This investigation focuses on the vibration technique , which uses the dynamic properties of the external tendon to infer the effective prestress force . Four large -scale external tendons , designed to simulate one section of an external tendon between two deviators in a post -tensioned bridge , were tested . In the study , damage to the tendons was induced in a quantifiable fashion at a specific location and the tensile force was measured directly . In addition , free -vibration tests were conducted periodically . This provided a direct means of measuring the sensitivity of measured natural frequencies and measured tensile force to local damage . The measured data were correlated with an approximation of the stiff string vibration model . In addition to the laboratory specimens , field testing was conducted on a bridge with external post -tensioned tendons . The findings from the study show that a loss in tensile force was not linear with a loss in the cross -sectional area of the strand , which results from stress redistribution within the tendon . Also , the natural frequencies were much less sensitive to the level of induced damage than the tensile force . While the measured data from the laboratory data compared very well with the analytical model , the field measurements exhibited a much greater deviation from the model . Due to several factors , the difference between the laboratory specimens and the bridge tendons are believed to be caused by larger levels of inherent error in the model . The findings from the investigation support the notion that vibration testing is most appropriately used in comparing relative differences between peer tendons .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -843
Date: 2010-10-21

Citation

Frequency response of damage [sic] external post-tensioned tendons. Master's thesis, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -05 -843 .

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