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Effects of Strong Motion Processing Procedures on Time Histories, Elastic and Inelastic Spectra

Effects of Strong Motion Processing Procedures on Time Histories, Elastic and Inelastic Spectra. By Paolo Bazzurro, Brian Sjoberg, Nicolas Luco (AIR) Walter Silva, Robert Darragh (Pacific Engineering and Analysis) Presented at COSMOS INVITED WORKSHOP ON STRONG-MOTION RECORD PROCESSING

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Effects of Strong Motion Processing Procedures on Time Histories, Elastic and Inelastic Spectra

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  1. Effects of Strong Motion Processing Procedureson Time Histories, Elastic and Inelastic Spectra ByPaolo Bazzurro, Brian Sjoberg, Nicolas Luco (AIR) Walter Silva, Robert Darragh (Pacific Engineering and Analysis) Presented at COSMOS INVITED WORKSHOP ON STRONG-MOTION RECORD PROCESSING Richmond, CA, May 26-27, 2004 www.air-worldwide.com

  2. Motivation • To quantify on a statistical basis the effects on ground motion time histories and elastic and inelastic spectra of • Causality of the filter • Filter order • Selection of the high-pass cut-off frequency • Preservation or removal of residual displacement offset • We considered • Butterworth filter only • Near-source (distance R17km) ground motions from earthquakes with moment magnitude ranging from 6.5 to 7.6 • Two components rotated fault-parallel and fault-normal

  3. Earthquakes and Recording Stations

  4. Processing Techniques Legend: Available Not Available * Parallel component only

  5. Response to Butterworth Filters of Different Orders

  6. Inelastic Displacement Response Spectra – What’s R?

  7. Effects of Causality of the Filter Bandwidth upper bound for acausal filter Bandwidth upper bound for causal filter Bandwidth for cascade acausal filter R=1 (Elastic)

  8. Effects of Causality of the Filter R=8 (Severely Inelastic)

  9. Effects of Filter Order: 4-pole vs. 5-pole Causal R=1 (Elastic) R=8 (Severely Inelastic)

  10. Effects of Filter Order: 4-pole vs. 5-pole Acausal R=1 (Elastic) R=8 (Severely Inelastic)

  11. Effects of Filter Order: 2p-2p vs. 2p-3p Acausal R=1 (Elastic) R=8 (Severely Inelastic)

  12. Effects of HP cut-off frequency: fHP vs. 1.5fHP --- 4-poleCausal Filter R=1 (Elastic) R=8 (Severely Inelastic)

  13. Effects of HP cut-off frequency: fHP vs. 1.5fHP --- 4-pole Acausal Filter R=1 (Elastic) R=8 (Severely Inelastic)

  14. Effects of HP cut-off frequency: fHP vs. 1.5fHP ---2p-2pCascade Acausal Filter ~5s 1.5s R=1 (Elastic) R=8 (Severely Inelastic)

  15. Effects of HP cut-off frequency: fHP vs. 1.5fHP ---2p-2pCascade Acausal Filter 0.5s 2.0s R=1 (Elastic) R=8 (Severely Inelastic)

  16. Effects of HP cut-off frequency: fHP vs. 1.5fHP ---2p-2pCascade Acausal Filter 1.0s 3.0s R=1 (Elastic) R=8 (Severely Inelastic)

  17. Effects of Residual Displacement R=1 (Elastic) R=8 (Severely Inelastic) Notes: 1) normal components 2) 6 records only 3) Results for causal filters are similar

  18. Summary of Effects of Processing Techniques on Elastic and Inelastic Spectra • In general, effects are larger • for inelastic than for elastic spectra and • for longer periods at any given response level (i.e., R=1 through 8) • Causality of the filter does not systematically affect the amplitude of the spectra. • The statistical impact on spectra due to the filter order is negligible • Increasing the value of the HP cut-off frequency, fHP, generates inelastic spectra that are systematically lower at periods much lower than 1/ fHP regardless of the causality of the filter. This can be in part explained by the lengthening of the effective period of vibration of structures in the post-elastic regime. • Records with residual displacement offset preserved generate inelastic response spectra that are consistently higher than those caused by records with offset removed. (Phenomenon observed for 6 fault-normal records only). NOTE: See paper for effects on spectra caused by applying a filter to simulated ground motion records

  19. Summary of Effects of Processing Techniques on Ground Motion TH’s • In general, effects are significant for PGD and, to a lesser extent, for PGV. The impact on other parameters (e.g., PGA, Arias Intensity, and duration) is negligible. • Causally filtered records have PGV and PGD values that are, on average, smaller (by 5-10% and 5-15%, respectively) than those of acausally filtered ones. • Acausally filtered records generally display a more prominent ramp of increasing displacement prior to the onset of strong-motion than causally filtered records. Peak-to-peak displacement amplitude, however, is similar for each processing technique. • The filter order does not affect the ground motion parameters considered here. • Increasing the value of the HP cut-off frequency, fHP, generates records with lower PGV and PGD values (5% and 15-20%, respectively), as expected. • The values of PGV and PGD are considerably larger (5-20% and 50-60%, respectively) in records with residual static offset preserved, as expected.

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