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
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Added mass on storys or roof
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Can use pools/water or A/C units
Added mass is a structural “cost” or liability
Typically quite small
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Small masses may thus be more effective for
lighter wind loads than for (large) seismic events
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Still, they have been widely implemented
How to Enhance the TMD
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If you could make the mass much larger, a greater
response reduction might be obtained
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But, … How would you dissipate the tuned mass
response energy most effectively?
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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
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Low-power
Highly efficiently
Customizable hysteresis (F vs Disp) loops
SATMD Concept
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Upper or new stories added as
segregated mass
 Connections are of resetable devices
and/or rubber bearings
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Use 1-4 devices to resist all motion
of upper stories and dissipate max
energy
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Goal 1: upper stories = tuned mass
 Goal 2: reduce displacements and
thus shears in lower stories
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How to tune?
2DOF system
Semi-Active
Mass Damper
Tuned Tuned
Mass Damper
systemsystem
upper stories (TMD)
(SATMD)
lower stories
1y1  c1c1 0c2y1   c2k1  y01 y1 k km1
m
1 1 0 0y
m
1
2

0 m y   0 0 y    0 0 y   0
2 22
m
y2     c2 2  c2  y 2 2   k 2
 0
0k 2 y11 y 1m1F 0 1
1  g   1 spring   yg


m
k 2 2y 2  0   m2 1
Tuning & Device Stiffness
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Easy Assumption = tune to 1st mode as with
passive TMD (PTMD)
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Better Assumption = tune lower than first mode
to enhance device motion and thus the energy
dissipated that can be dissipated
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Set SATMD stiffness to PTMD/5
Under PTMD/2 works pretty much equally well
Method – Spectral Analysis
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Run suites of earthquakes and develop spectra
• SAC project ground motions
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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
Linear Spectra Results
Low
Medium
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High
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
Linear System Results
Passive vs Semi-Active
(Low), Medium, [High] Suite
Results in all cases
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”
Non-Linear Case – Low Suite
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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 semiactive solution
SATMD < 100% still even at
84th 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
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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.
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PTMD results are very wide and do not always reduce response –
even with optimal tuning to first mode!
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Therefore, it is very easy to design tuning
Solution will not degrade as structure changes over time
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
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Approach is basically the same as presented for directly controlled
structures in prior work
Acknowledgments
 EQC
 All
Research Foundation Grant #03/497
co-authors and contributors