Bending Stresses in Stay-Cables During Large-Amplitude Vibrations - A Fred Hartman Bridge Case Study

After the 1996 completion of the Fred Hartman Bridge in Houston, Texas, there were several occasions when large-amplitude lateral vibrations of its stay-cables were observed. Whereas the exact cause of these vibrations has yet to be determined, the installation of Freyssinet dampers, the stiffening of the anchorage guide pipes, and the reinstallation of cable restrainers have since prevented reoccurrence of the vibrations. Despite the successful mitigation, there still remains a question about the effects these vibrations may have had on the stay-cables and their service/fatigue life. To address it, this work aims primarily at the determination of the bending stresses that arose in the cables during the observed large-amplitude vibrations, as a precursor to quantifying the cables’ fatigue life. In this context, this work draws from the field observations and laboratory experiments conducted under the auspices of a multi-year comprehensive investigative program funded by the Texas Department of Transportation, to arrive at a synthesis of observations, experiments, and computational models that may explain the observed stay-cable behavior. To this end, and with the primary goal of bending stress quantification in mind, a number of necessary secondary issues were also addressed; these include:

a. a plausible scenario for the observed large-amplitude vibrations;

b. computational models consistent with the field observations;

c. computational models for a series of cable fatigue-related experiments conducted at the Ferguson Structural Engineering Laboratory at the University of Texas at Austin over the course of the last two or three years;

d. correlation of the field with the laboratory observations; and

e. development of testing guidelines for a new series of bending fatigue tests based on the findings of this work.