Changes in modal parameters of a bridge during fatigue testing |
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Authors: | H J Salane J W Baldwin |
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Institution: | (1) Civil Engineering Department, University of Missouri-Columbia, 65211 Columbia, MO |
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Abstract: | The effects of high-cycle fatigue on the dynamic modal properties of a full-scale bridge test section are examined in this
study. A span 30.5 m (100 ft) in length was salvaged from an interstate bridge for experimental testing to establish the fatigue
performance of the retrofit procedures which could be used for future field repairs of the fatigue cracks. Horizontal cracks
had formed in the webs of the twin bridge girders in the vicinity of the web-flange weld at or near the connections of the
girders to the floor beams. An electrohydraulic vibration shaker was used to excite the test span in the torsional and bending
modes to promote fatigue crack growth. In addition to the experimental evaluation of the retrofit procedures, the dynamic
response characteristics of the test span during the high-cycle fatigue test were monitored. Experimental data have been used
to establish mode shapes and modal damping ratios during the four-million-cycle fatigue test. Damping ratios ranged from 1.09
percent to 0.53 percent. Modal stiffnesses were calculated based on the experimental mode shapes. There is a modest correlation
between the changes in stiffness and the observed cracking of the steel girders and the subsequent repairs.
Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Porland, OR on June 5–10. |
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