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 Can use pools/water or A/C units Added mass is a structural “cost” or liability Added mass is a structural “cost” or liability Typically quite small 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

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) Viscous dampers (high force transmission) Lead-rubber bearings (don’t necessarily re-center) Lead-rubber bearings (don’t necessarily re-center) Active (high energy/power source required) Active (high energy/power source required)  Semi-active may offer the most opportunity Low-power Low-power Highly efficiently Highly efficiently Customizable hysteresis (F vs Disp) loops Customizable hysteresis (F vs Disp) loops

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?

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

Tuning & Device Stiffness  Easy Assumption = tune to 1 st 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 Set SATMD stiffness to PTMD/5 Under PTMD/2 works pretty much equally well Under PTMD/2 works pretty much equally well

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

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 High Medium

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

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 84 th percentile

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.

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 Therefore, it is very easy to design tuning Solution will not degrade as structure changes over time 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 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 Approach is basically the same as presented for directly controlled structures in prior work

Acknowledgments  EQC Research Foundation Grant #03/497  All co-authors and contributors