Semi-Active Tuned Mass Damper Systems

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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

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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

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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 (dont 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

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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?

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

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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

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Linear Spectra Results
Low
Medium

• SATMD is much narrower than PTMD
• All SATMD values lt 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

High
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Linear System Results Passive vs Semi-Active
(Low), Medium, High Suite Results in all cases
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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 lt 100 still even at 84th percentile

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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, its
easy to tune/design.
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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

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Acknowledgments

• EQC Research Foundation Grant 03/497
• All co-authors and contributors