Generating damping modification factors after artificial inputs in scenarios of local records scarcity

Abstract

The damping modification factors are utilized to alter the design spectral ordinates for constructions whose damping differs significantly from 5%, this being the level that is routinely considered by most codes. Such factors are habitually evaluated after suites of historical inputs representing the local seismicity. However, such records may not be readily available, due either to moderate seismicity or to limited seismological network; in such cases, representative artificial accelerograms might be used instead. This paper proposes a methodology for establishing damping modification factors after artificial inputs generated to match the 5% design spectra; this approach can be used for countries, regions or cities. The proposed methodology is based on performing dynamic analyses on underdamped and overdamped SDOF linear systems by using the aforementioned selected accelerograms. Although previous studies have highlighted the differences among factors generated after natural and artificial inputs, it has been observed that such discrepancies are mainly due to the longest significant (Trifunac) duration of the artificial accelerograms. Therefore, the artificial inputs are generated as their duration fits those of the available local strong motion records. An application to Colombia is presented; the results are compared with those for some available Colombian records. The sensitivity of the calculated factors to the soil type, period and seismic zone is investigated; matching expressions are provided. Such expressions are compared with the prescriptions of major design codes and with other studies. The suitability of the proposed formulation is further verified in an example on an isolated hospital building.