Quantification of fundamental frequency drop for unreinforced masonry buildings from dynamic tests

The knowledge of fundamental frequency and damping ratio of structures is of uppermost importance in earthquake engineering, especially to estimate the seismic demand. However, elastic and plastic frequency drops and damping variations make their estimation complex. This study quantifies and models the relative frequency drop affecting low-rise modern masonry buildings and discusses the damping variations based on two experimental datasets: Pseudo-dynamic tests at ELSA laboratory in the frame of the ESECMASE project and in situ forced vibration tests of EMPA and EPFL. The relative structural frequency drop is shown to depend mainly on shaking amplitude, i.e. structural effects, whereas the damping ratio variations could not be explained by the shaking amplitude only. Therefore, apparently the absolute frequency value depends mostly on the frequency at low amplitude level, the amplitude of shaking and the construction material. The decrease shape does not vary significantly with increasing damage. Hence, this study makes a link between structural dynamic properties, either under ambient vibrations or under strong motions, for low-rise modern masonry buildings. A value of 2/3 of the ambient vibration frequency is found to be relevant for earthquake engineering assessment for this building type. However, this study does not account for soil-structure interaction that may also affect these parameters.

MICHEL C.;  ZAPICO BLANCO Beatriz;  LESTUZZI P.;  MOLINA RUIZ Francisco Javier;  WEBER F.; 

2011-08-25

JOHN WILEY & SONS LTD

JRC62786

0098-8847,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC62786,   

10.1002/eqe.1088,