Civil Engineering Reference
In-Depth Information
up to 5.81 %. In general, although the upper bound estimated based on the SSI method is 6 %, there is not a clear trend in the
results observed. The results obtained with the EFDD method seem to have a better agreement with the expectation of an
increment as the acceleration increases.
11.5 Conclusions
The results observed in the assessment of the damping ratio using the simple 3-DOF's lumped mass model suggest an
increment of the damping ratio with the amplitude of the external excitation. This observation is in good agreement to what
was observed in the evaluated bridges, in which the damping ratio values - estimated by using the EFDD method- are below
2.5 % for low levels of vibration, produced by ambient vibrations or weak ground motion. However, according to the results
obtained using ground motion data, this independency of the frequency content of the excitation is not directly extended to
the lateral damping of bridges. These results show different damping ratios for ground motions with similar intensity applied
to the same bridge. As far as the authors' knowledge, the bridges included in the database did not exhibit structural damage
caused by the recorded events, even for the stronger ground motions. Therefore, further investigation is recommended to
evaluate the inconsistency in the damping values estimated based on ground motion data calculated by the EFDD and the
SSI methods.
Acknowledgements
The first author acknowledges the support provided by the University of Medellin, Colombia. This study was also conducted
with financial support from the Ministry of Transportation of British Columbia, Canada and the Natural Sciences and Engineering Research
Council of Canada.
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