Correction of Acceleration Records From Free Vibration Tests on Base Isolated Buildings.


Abstract eng:
A three-story reinforced concrete building in Augusta (Sicily, Italy), isolated at the base and designed according to the provisions of the latest Italian seismic regulations, was subjected to a series of push and sudden release tests in March 2013. The isolation system consisted of 16 high damping rubber bearings and 20 low friction sliding bearings. The release tests were performed at low amplitudes to ensure that no damage would occur in the building; the imposed displacements varied from 5.8cm to 11.7cm (isolator demand γ max =0.39-0.78). During the tests, the displacements at the isolation level were measured along with the accelerations at each floor of the building. Once the tests were completed, the observed structural response was used for the assessment of the properties of the isolation system. Before input in analyses, the signals were treated for the removal of low frequency noise using a simple baseline fitting scheme. The developed signal processing scheme consists in defining the duration of the main event, removing the background noise and using polynomial curves for the adjustment of the signal reference baseline. The method does not require significant computational effort and accounts for boundary conditions, provided that these are known. The polynomial coefficients used in the baseline fitting of the signals are determined from the boundary conditions; namely the initial and end accelerations, velocities and displacements. The deterministic definition of the polynomial coefficients and the recovery of permanent displacements enforces the reliability of the method and makes it an attractive alternative to high pass filtering, which instead requires proficient users and includes a lot of subjectivity in the filter parameter selection. The proposed baseline scheme is applied herein for the adjustment of the absolute and relative acceleration signals obtained from test 9, one of the tests with the highest initial input (u 0 =10.1cm). Implementation of the method provides the adjusted response in terms of absolute and relative floor accelerations, velocities and displacements. The processed absolute accelerations and velocities are zero when the motion starts and when the motion ceases; while the absolute ground floor displacement equals the experimental (measured) initial displacement at the beginning of motion and the experimental residual displacement at the end of motion. The predicted ground floor displacement matches very satisfactorily the displacement measurement. The developed method is implemented moreover on the relative to the base acceleration signals, for the evaluation of the relative displacement and velocity response of the superstructure. The method assures that the relative response is zero at the beginning and end of motion, since the superstructure remains elastic under such small excitation. The relative response is evaluated in two ways: (i) subtracting the adjusted ground floor response from the adjusted upper floor response and (ii) processing the raw relative motions. The implementation of methodologies (i) and (ii) provides identical relative accelerations and velocities, enforcing the reliability of the method. The relative displacements are high pass filtered to remove the effect of long period noise in the second half period of motion, where the signal amplitude is significantly small and the noise is probably predominant.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
Text je chráněný podle autorského zákona č. 121/2000 Sb.



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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 1716.:
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