Off-Diagonal 2-4 Damping Technology using Off-Diagonal 2-4 Damping Technology using Semi-Active Resetable DevicesSemi-Active Resetable Devices

Geoffrey W RodgersGeoffrey W Rodgers, Kerry J Mulligan, J Geoffrey Chase, John B Mander, , Kerry J Mulligan, J Geoffrey Chase, John B Mander,

Bruce L Deam, and Athol J CarrBruce L Deam, and Athol J Carr

End Cap

Cylinder

Piston

Seal

Device DesignDevice Design

Valvea)

Valves

Cylinder Piston

b)

Cylinder Piston

Independent two chamber design allows broader range of control laws

Overall Customised HysteresisOverall Customised Hysteresis

Only the 2 - 4 control law does not increase base-shear

Viscous Damper

1-4 Resetable

1-3 Resetable

2-4 Resetable

Resist all motion

Resist motionaway from 0

Resist motiontoward 0

Resist all velocity

Semi-Active Resetable Device ModelSemi-Active Resetable Device Model

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Experimental Test Results

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Simulink Models

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Simplified Linear ModelSimplified Linear Model

Less computationally expensive, with no anticipatedloss of accuracy or generality

1-3 control 2-4 control

1-4 control

Response SpectraResponse Spectra

Average response spectra for different control laws

How do the different control laws perform relative to one another?

Reduction FactorsReduction Factors

More clearly represent reductions achieved with each control law

Note the apparent invariance to the type of ground motion encountered

Divide results with additional stiffness by the uncontrolled case

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

Suite DependenceSuite DependenceNormalise 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 ResultsSpread 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 ForceStructural ForceThe 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 metricSimilar performance for the 1-3 and 2-4 devices

Base-ShearBase-ShearThe 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 comparedControl laws comparedAveraging 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 AreaDisplacement Spectral AreaNumerically 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

BR /1 wherestructural

resetable

K

KCB 1

where C = 1.43, 1.59, and 5.75 for the 1-3, 2-4 and 1-4 devices

How accurate are these equations?How accurate are these equations?

Re-plot the displacement reduction factors, with the reduction factors from the empirical equations

Although variations can be seen above T = 3.0seconds, equations are appropriate over the constant velocity region from T = 0.5 – 3.0 secs

Black Line is Empirical Equation

ADRS 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.

SummarySummary

• 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

ConclusionsConclusions

• 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

• 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 WorkExperimental WorkOne fifth scale building fitted with pneumatic

semi-active resetable devices

Experimental and Analytical Experimental and Analytical ComparisonComparison

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El Centro 70% - Displacement Structural Response

Valves Open1-4 Control Law2-4 Control Law

Reductions seen in shake table tests are close to those predicted by the analytical study

AcknowledgementsAcknowledgements

Special thanks to Ms Kerry Mulligan and Professors Special thanks to Ms Kerry Mulligan and Professors Chase and Mander for their assistance with this research, Chase and Mander for their assistance with this research,

as well as to our co-authorsas well as to our co-authors

This research was funded by the NZ Earthquake Commission This research was funded by the NZ Earthquake Commission (EQC) Research Foundation and the New Zealand Tertiary (EQC) Research Foundation and the New Zealand Tertiary Education Commission (TEC) Bright Futures Top Achievers Education Commission (TEC) Bright Futures Top Achievers

Doctoral Scholarship SchemeDoctoral Scholarship Scheme