Comparison between DRF for displacement and acceleration spectra with uncertain damping for EC8

Abstract

The damping force exerted by a structure during an earthquake differs significantly from that specified in the design process. This introduces uncertainties in the design process of structures under earthquake loads. Accordingly, it is desirable to consider not only the effect of randomness of the seismic load but also the uncertainties in the structural parameters. This paper investigates the effect of uncertainties inherent in the damping ratio on the use of damping reduction factor (DRF) for the evaluation of high damping response spectra for linear structures with viscous damping. The DRFs are evaluated from both acceleration and displacement response spectra. Effects of period of vibration, level of damping ratio, soil class and uncertainties level of damping on the DRFs are evaluated and discussed. A numerical analysis implies that the maximum relative error estimated between the deterministic DRF and the DRF considering uncertainties in damping is about 14%. This implies that the damping uncertainty with = 20% leads to an error in DRF of Cv=13 % which is a significant error in estimating the structure response.

Keywords

• civil engineering
• earthquake engineering
• structural engineering