Quantification of fundamental frequency drop for unreinforced masonry buildings from dynamic tests |
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| Authors: | C Michel B Zapico P Lestuzzi F J Molina F Weber |
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| Institution: | 1. Ecole Polytechnique Fédérale de Lausanne (EPFL), Applied Computing and Mechanics Laboratory (ENAC‐IIC IMAC), Switzerland;2. ETH Zürich, Swiss Seismological Service, Switzerland;3. European Commission, Joint Research Center, IPSC, European Laboratory for Structural Assessment (ELSA), Italy;4. ARUP VB, Bridges Department, The Netherlands;5. Swiss Federal Laboratories for Materials Science and Technology, Structural Engineering Research Laboratory, Switzerland |
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| Abstract: | 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 data sets: Pseudo‐dynamic tests at ELSA laboratory in the frame of the ESECMaSE project and in situ forced vibration tests by EMPA and EPFL. The relative structural frequency drop is shown to depend mainly on shaking amplitude, whereas the damping ratio variations could not be explained by the shaking amplitude only. Therefore, the absolute frequency value depends mostly on the frequency at low amplitude level, the amplitude of shaking and the construction material. The decrease in 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 the earthquake engineering assessment for this building type. However, the effect of soil–structure interaction that is shown to also affect these parameters has to be taken into account. Therefore, an analytical methodology is proposed to derive first the fixed‐base frequency before using these results. Copyright © 2010 John Wiley & Sons, Ltd. |
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| Keywords: | unreinforced masonry fundamental frequency damping ratio seismic demand pseudo‐dynamic tests forced vibrations ambient vibrations |
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