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Semi-Active Tuned Mass Damper Systems

Semi-Active Tuned Mass Damper Systems. K.J. Mulligan, M. Miguelgorry, V. Novello, J.G. Chase, G. Rodgers, & B. Horn, J.B. Mander, A. Carr & B.L. Deam. Current TMDs. Added mass on storys or roof Can use pools/water or A/C units Added mass is a structural “cost” or liability

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Semi-Active Tuned Mass Damper Systems

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  1. Semi-Active Tuned Mass Damper Systems K.J. Mulligan, M. Miguelgorry, V. Novello, J.G. Chase, G. Rodgers, & B. Horn, J.B. Mander, A. Carr & B.L. Deam

  2. Current TMDs • Added mass on storys or roof • Can use pools/water or A/C units • Added mass is a structural “cost” or liability • Typically quite small • Small masses may thus be more effective for lighter wind loads than for (large) seismic events • Still, they have been widely implemented

  3. How to Enhance the TMD • If you could make the mass much larger, a greater response reduction might be obtained • But, … How would you dissipate the tuned mass response energy most effectively? • Viscous dampers (high force transmission) • Lead-rubber bearings (don’t necessarily re-center) • Active (high energy/power source required) • Semi-active may offer the most opportunity • Low-power • Highly efficiently • Customizable hysteresis (F vs Disp) loops

  4. SATMD Concept • Upper or new stories added as segregated mass • Connections are of resetable devices and/or rubber bearings • Use 1-4 devices to resist all motion of upper stories and dissipate max energy • Goal 1: upper stories = tuned mass • Goal 2: reduce displacements and thus shears in lower stories • How to tune?

  5. 2DOF system Semi-Active Tuned Mass Damper system Tuned Mass Damper system upper stories (TMD) upper stories (SATMD) lower stories

  6. Tuning & Device Stiffness • Easy Assumption = tune to 1st mode as with passive TMD (PTMD) • Better Assumption = tune lower than first mode to enhance device motion and thus the energy dissipated that can be dissipated • Set SATMD stiffness to PTMD/5 • Under PTMD/2 works pretty much equally well

  7. Method – Spectral Analysis • Run suites of earthquakes and develop spectra • SAC project ground motions • Compare PTMD with SATMD using 100% resetable devices • Use upper story mass equal to 20% of lower story mass as the SATMD/PTMD mass • Present 16th, 50th and 84th percentile results (lognormal) • Assume optimal tuning in PTMD for most conservative comparison (i.e. best PTMD results) • All results presented as reduction factors of base structure (y1) motion as compared to uncontrolled case and presented as a percentage (%) • Analyse some suites with non-linear structure for more realistic comparison and analysis • Shows effect of realistic non-linearity and structural yielding on system performance

  8. Linear Spectra Results • SATMD is much narrower than PTMD • All SATMD values < 100% • PTMD highly variable over suites • Differences are greatest in 1-3 second range of greatest interest for earthquakes • Again, optimal PTMD tuning is used Low Medium High

  9. PTMD does better for the “right” ground motion PTMD does much worse for the “wrong” ground motion 16th – 84th range (%) at T = 2s RTMD is thus more “consistent” Linear System Results Passive vs Semi-Active (Low), Medium, [High] Suite Results in all cases

  10. Non-Linear Case – Low Suite • Only low suite or most common events (1 in 72yrs) • Bouc-Wen model for structural non-linearity and yielding (3%) • Similar results overall to linear spectra case • PTMD even wider over suite with non-linear structure as might be expected • SATMD only a little wider showing adaptability of semi-active solution • SATMD < 100% still even at 84th percentile

  11. Non-linear Case Results PTMD still does better for the “right” ground motions PTMD now much worse for the “wrong” ground motions RTMD is more “consistent” Semi-active ability to adapt to non-linear response prevents degradation for RTMD case that can occur in passive tuned PTMD case. Plus, it’s easy to tune/design.

  12. SATMD Summary • Concept shows significant promise in an area that may grow as developers and others seek to go “upwards” where they cant go “out” • Provides a novel way to obtain TMD like results without added mass • SATMD tuning does not require knowledge of exact masses or exact first mode frequency, as with standard passive PTMD. • Therefore, it is very easy to design tuning • Solution will not degrade as structure changes over time • PTMD results are very wide and do not always reduce response – even with optimal tuning to first mode! • SATMD approach does not rely on a ground motion with the “right frequency content” to occur to get an improved result over uncontrolled • Reduction factor spectra over suites of events can be used to create design equations and integrate into standard performance-based design methods • Approach is basically the same as presented for directly controlled structures in prior work

  13. Acknowledgments • EQC Research Foundation Grant #03/497 • All co-authors and contributors

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