Transcript Slide 1

Off-Diagonal 2-4 Damping Technology using
Semi-Active Resetable Devices
Geoffrey W Rodgers, Kerry J Mulligan, J Geoffrey Chase, John B Mander,
Bruce L Deam, and Athol J Carr
End Cap
Seal
Cylinder
Piston
Device Design
a)
b)
Valve
Valves
Cylinder
Piston
Cylinder
Piston
Independent two chamber design allows broader range of control laws
Overall Customised Hysteresis
Resist all velocity
Viscous Damper
Resist all motion
1-4 Resetable
Resist motion
away from 0
1-3 Resetable
Resist motion
toward 0
2-4 Resetable
Only the 2 - 4 control law does not increase base-shear
Semi-Active Resetable Device Model
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Force (N)
Force (N)
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1000
0
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0
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-10
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0
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10
Piston Displacement from Centre Position (mm)
-3000
-15
15
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1000
Force (N)
Force (N)
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0
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0
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-500
-1000
-1000
-1500
-1500
-2000
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-5
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Piston Displacement from Centre Position (mm)
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Simulink Models
Experimental Test Results
500
-10
-5
0
5
10
Piston Displacement from Centre Position (mm)
-2000
-20
-15
-10
-5
0
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Piston Displacement from Centre Position (mm)
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Simplified Linear Model
1-3 control
2-4 control
1-4 control
Less computationally expensive, with no anticipated
loss of accuracy or generality
Response Spectra
Average response spectra for different control laws
How do the different control laws perform relative to one another?
Reduction Factors
Divide results with additional stiffness by the uncontrolled case
More clearly represent reductions achieved with each control law
Largest reductions seen for the 1-4 device – This device acts
over a larger percentage of each cycle and will consequently
have longer active strokes
Note the apparent invariance to the type of ground motion encountered
Suite Dependence
Normalise the average reduction factor from each suite
to the reduction factors for all ground motions to
investigate suite dependence
Values close to unity across the spectrum indicates an invariance
to the type of ground motion (near field vs. far field) encountered
– indicating a robustness of this form of control
Spread of Results
Log-normal co-efficient of variation or dispersion factor
- Indicates the spread of the results within a ground motion suite
- Largest spread is seen for the 1-4 device indicating more variability
- Both the 1-3 and 2-4 device show a tighter spread
Structural Force
The base-shear force for a linear, un-damped structure
- Gives an indication of the required column strength
Largest reductions for the 1-4 device – consistent with other metric
Similar performance for the 1-3 and 2-4 devices
Base-Shear
The sum of the structural force and the resetable device force
- Gives an indication of the required foundation strength
Only the 2-4 device reduces base shear across the entire spectrum
The 1-3 and 1-4 devices increase base-shear by as much as 60%
The 2-4 device provides similar reductions in displacement and
structural force as the 1-3 device, and also reduces base-shear
Control laws compared
Averaging across suites more clearly indicates
the relative advantage of the control laws
Structural Force
Base-Shear Force
1-3 and 2-4 show similar reductions in structural force, but are
outperformed by the 1-4 device
Only the 2-4 device reduces base-shear, whereas both the 1-3 and
1-4 increase base-shear by as much as 60%
Displacement Spectral Area
Numerically integrate the area under the response spectra in the seismically
important T = 0.5 to 2.5 second range.
An indication of the average displacement reduction factor in the constant
velocity region of the spectra
Fit empirical equations to estimate damping reduction factors
R  1 / B where B  1  C
K resetable
K structural
where C = 1.43, 1.59, and 5.75 for the 1-3, 2-4 and 1-4 devices
How accurate are these equations?
Re-plot the displacement reduction factors, with the
reduction factors from the empirical equations
Black Line is
Empirical Equation
Although variations can be seen above T = 3.0seconds, equations are
appropriate over the constant velocity region from T = 0.5 – 3.0 secs
ADRS
Acceleration-Displacement Response Spectra
Relate additional resetable stiffness to design guidelines
Empirical reduction factor equations create a “standard
design platform” for a structural engineer to safely and
effectively add resetable devices to their design.
Summary
• The 1-4 device outperforms both the 1-3 and 2-4 device for
displacement response and structural force as it acts over the full
response cycle, has longer active strokes, and consequently higher
energy dissipation
• Both the 1-3 and 1-4 devices provide a reduction in structural force
and displacement response, but increase base-shear up to 60%
• The 2-4 device reduces both structural force and base-shear
• All three control laws are suite invariant indicating a robustness to the
type of ground motion encountered
• Empirical equations to approximate reduction factors allow
incorporation into accepted performance based design metrics
Conclusions
• Semi-active control enables customisation of overall structural
hysteresis in novel ways not available with passive systems
• The most applicable control law (of the selected few presented)
depends on the application
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New purpose designed structure
Retrofit application with limited foundation strength
Thus, device selection and implementation is a structural design problem rather
than a control systems problem
• The overall approach presented can be used to develop standard
design metrics for any similar novel semi-active or passive
systems/devices, thus creating a bridge to the design profession and
a greater likelihood of uptake.
Experimental Work
One fifth scale building fitted with pneumatic
semi-active resetable devices
Experimental and Analytical
Comparison
Reductions seen in shake table tests are close
to those predicted by the analytical study
El Centro 70% - Displacement Structural Response
20
Valves Open
1-4 Control Law
2-4 Control Law
15
Displacement (mm)
10
5
0
-5
-10
-15
-20
10
15
20
time (s)
25
30
Acknowledgements
Special thanks to Ms Kerry Mulligan and Professors
Chase and Mander for their assistance with this research,
as well as to our co-authors
This research was funded by the NZ Earthquake Commission
(EQC) Research Foundation and the New Zealand Tertiary
Education Commission (TEC) Bright Futures Top Achievers
Doctoral Scholarship Scheme