Shake Table Control Fidelity in Signal ...nees.ucsd.edu/eot/docs/2010-user-perspective-seismic-testing/UCSD... · Fidelity in Signal ReproductionFidelity in Signal Reproduction &

Shake Table ControlFidelity in Signal ReproductionFidelity in Signal Reproduction & Sources of Signal Distortion

Joel P. Conte, Professor, UCSDJ. Enrique Luco, Professor, UCSD

O O lik A i t t P f D k E l l U i T kOzgur Ozcelik, Assistant Professor, Dokuz Eylul Univ., Turkey

NEES@UNevada‐RenoNEES@UBuffaloNEES@UC San Diego

Shake Table Training Workshop 2010 – San Diego, CA

Components of a Shaking Table Testing Facilityand NEES-UCSD Shake Tableand NEES UCSD Shake Table

MECHANICALMECHANICAL

Components and Interaction Diagram

Specimen

PlatenActuators

BearingsSurrounding

SoilReaction

Block

MECHANICALSpecimen

PlatenActuators

BearingsSurrounding

SoilReaction

Block

MECHANICAL

Servovalves Accumulators BlowdownValves

Accumulators SurgeTank Pumps Accumulator

BankCommand

Signal

Controller Servovalves Accumulators BlowdownValves

Accumulators SurgeTank Pumps Accumulator

BankCommand

Signal

Controller

Tank BankSignal

ELECTRONIC HYDRAULIC

Tank BankSignal

ELECTRONIC HYDRAULIC

UCSD NEES Shake Table (LHPOST) located at Englekirk Structural Engineering Center located• UCSD-NEES Shake Table (LHPOST) located at Englekirk Structural Engineering Center located15 km East of UCSD campus.

• Unique facility enabling next generation seismic experiments to be conducted on full/large-scalestructural and soil-foundation-structure interaction systems.


structural and soil foundation structure interaction systems.

Ideal Shaking Table vs. Reality Ideal shaking table:

Reproduces commanded motion exactly Is characterized by a transfer function with unit gain and zero phase shift

over its entire operating frequency range under loaded table condition.

1

1.5

)|IdealReality

0 5 10 15 20 250

0.5

Frequency [Hz]

|H(

Due to various peaks and valleys in the shaking table

Frequency [Hz]

1

0

1

2

[rad]

IdealReality

system transfer function, the signal reproduced by the table differs from the commanded signal.

0 5 10 15 20 25-4

-3

-2

-1

Frequency [Hz]

< (j

)


Frequency [Hz]

Sources of Signal Distortion Many potential sources of distortion and many of them are highly

interdependent:

(1) Hydraulic sources: (1) Hydraulic sources:• Servovalves (inherently nonlinear devices)• Oil Column resonance• Changes in the pressure supply/demandg y• Flow limits• Force limits• Leakage flow in servovalves and actuators

(2) Mechanical sources:• Dissipative/Frictional forces• Mechanical resonances• Linear/Nonlinear specimen - table interaction• Backlash (bolted connection within the load train, actuator swivel)


High-flow High-performanceServovalves

Pilot Stage3 t

3rd Stage

4 t

3-stage Servovalve

th

4-stage Servovalve

4th Stage

Load flow ports(port windows)

Main pressureentrance

Courtesy of MTSSystems Inc


Systems Inc.

Hydraulic - ServovalvesActuator Extent DirectionActuator Extent Direction Actuator Retract DirectionActuator Retract Direction

SP

P

vxActuator Extent Direction

SP

P

vxActuator Extent Direction

SP

P

vx

Actuator Retract Direction

SP

P

vx

Actuator Retract Direction

K Fl i (li i d fl ffi i t)

2P

V

1A2A

RP1 2

1P2P

V

1A2A

RP1 2

1P 1A2A

RP 3 4

1P2P

V

1A2A

RP 3 4

1P2P

V

1 1 1 1v v Sq A V K w x P P

2 2 2 2v v Rq A V K w x P P xv : 4th stage valve spool displacement.

Kv : Flow gain (linearized flow coefficient)wi : Valve port window widthsA1, A2 : The tension and compression areas

3 1 3 1v v Rq A V K w x P P

4 2 4 2v v Sq A V K w x P P v

1 2and P P

1 2and P P

Ps , PR : Supply and return system pressures.

: Actuator chamber pressures during extent direction.

: Actuator chamber pressures during retract direction.

Servo-valve flows present two independent sources of nonlinearity:• Load pressure nonlinearity or pressure drop - flow nonlinearity (explicitly represented by the square root term),

• Flow gain nonlinearity (Kv changes due to variable size orifice)


g y ( v g )

Load Pressure Nonlinearity (Bernoulli’s Equation)N li d A t t F N li d Pi t V l it

1.5y y y

Quadrant IQuadrant II

Normalized Actuator Force vs. Normalized Piston Velocity2

1o oo

o v

V VFV x

1vx <0

0.5

1

uato

r Pis

ton

Vel

ocity

V 0 o v

Normalized Servo-valve Spool Displacement

oVx oVV

V

-1 5

-1

-0.5

Nor

mal

ized

Act

u

xv =.2xv =.4xv =.6xv=.8xv=1.0

Quadrant III

Quadrant IV

V

Observations (Direct Results of Bernoulli’s Equation):

1v

oo

o

xV FV

where maxV

maxo

FFF

-1 -0.5 0 0.5 11.5

Normalized Actuator Force

F0

1

c o s ( ) a n d F s i n ( )o o o oV V F

0 . 8, 0 . 8V F ( q )• Nonlinearity of flow (proportional to the piston velocity) - load

pressure relation increases with increasing load pressure.• Non-linearity between piston velocity and actuator force is also a

function of spool/valve opening0.2

0.4

0.6

0.80 . 8, 0 . 8o oV F0 . 6, 1 . 0o oV F

Pressure Switching Points

v function of spool/valve opening.• Severe non-linearity in spool opening as the system passes

through the peak force (at zero velocity) and the peak force islarge relative to Fmax= A x PS. This motion discontinuity is also

f d t “ it hi ”-0.6

-0.4

-0.2

0x v


referred to as “pressure switching”.

0 30 60 90 120 150 180 210 240 270 300 330 360-1

-0.8

θ

Th li fl i t th li fl di h th h i bl

Flow Gain Nonlinearity – Discharge Effect

1/ SdK wC P

The non-linear flow gain represents the non-linear flow discharge through a variablesize orifice: the flow discharge rate decreases with increasing orifice area.

where Cd = discharge coefficient 1/v SdK wC P d g

Typical Flow vs Spool Opening Curve (Zhao et al., 2005)

Lx P

Orifice Flow Equation

gpm

]

1 1,2v LL v v

v S

x PQ K x ix P

QL

[g

PL/PS ratio is kept

constant.

High velocity/flow signals suffer from this source of non-linearity.

Spool Opening xv [%]


High velocity/flow signals suffer from this source of non linearity.

Flow Gain Nonlinearity - Hydraulic Pressure Effect

1/K C w P

Hydraulic supply pressure fluctuates especially as the hydraulic demand is high.Inertial pressure spikes can cause noise and result in increased signal distortion.

where C = discharge coefficient 1/v SdK C w P

1994 Northridge Earthquake0.6

1

[g] Cmd Signal

Fbk Signal

where Cd = discharge coefficient

1994 Northridge Earthquake recorded at Sylmar Station (Seven-story R/C building

specimen mounted on the table)

43 5 44 44 5 45 45 5-0.6

-0.2

0.2

Acc

eler

atio

n

43.5 44 44.5 45 45.5

3000

3100

3200

psi] Change in supply pressure PS at

43.5 44 44.5 45 45.52700

2800

2900

Time [sec]

Ps [p West actuator during test


Effect of Load Pressure Nonlinearityon Fidelity in Signal Reproduction

Sine Tests @ 3 Hz (Bare Table)

7

FFT of the Sp07 Test Fbk Signal

on Fidelity in Signal Reproduction

0

2

atio

n [g

] - S

p07

Cmd SignalFbk from Test

600

700 ExcitationFrequency

3.4 3.45 3.5 3.55 3.6 3.65

-2

Acc

eler

a

6p09

C d Si l300

400

500

|Sp0

7(j

)|

OddHarmonics

-4-2024

eler

atio

n [g

] - S

p Cmd SignalFbk from Test

100

200

Harmonics

1.4 1.45 1.5 1.55 1.6 1.65-64

Time [sec]

Acc

e

0 5 10 15 20 250

Frequency [Hz]

High acceleration signals suffer from load pressure non-linearity.


g g p y

Example of Signal Distortion from UNAM Shake Table - Time HistoriesU S a e ab e e sto es

5

m/s2 ]

Cmd SignalFbk SignalSine Test @ 1 Hz

10

15

]

Cmd SignalFbk Signal 0

Acc

eler

atio

n [m

0

5

cele

ratio

n [m

/s2 ]

15 Cmd SignalFbk Signal

1 1.5 2 2.5 3-5

Time [sec]

-10

-5Acc

0

5

10

erat

ion

[m/s2 ]

Fbk Signal

0 2 4 6 8 10 12 14 16 18-15

Time [sec]

8 8.5 9 9.5 10-15

-10

-5

Acc

ele


8 8.5 9 9.5 10Time [sec]

Example of Signal Distortion from UNAM Shake Table – Fourier Spectra

x 105

pSine Test @ 1 Hz

6

7

ExcitationFrequency

4

5

|Y(j

)| OddHarmonics

2

3

| Harmonics

0 5 10 15 20 25 30 35 400

1


Frequency [Hz]

Simulation of Signal Reproduction with “Linearized” Servovalve

Servo-valve Rated Flow GainLinearization of the Flow Equation

(Bernoulli’s Equation)4

6

CommandedMeasuredPredicted - Nonlinear SVPredicted - Linear SV

Flow [lt/min]

10,000 lt/m@ 1000 psi

Flow [lt/min]

10,000 lt/m@ 1000 psi

0

2

ratio

n [g

] - S

p09

1

Rsvk

1

Rsvk

-4

-2

Acc

eler

4th StgSpool Stroke

maxsvx 4th Stg

Spool Strokemaxsvx

S l Fl G iLinearization of servovalves can be achieved by

1.4 1.45 1.5 1.55 1.6 1.65-6

Time [sec]

3Rsv svk k

Servo-valve Flow Gain @ 3000psi - Linear

(1) inverse nonlinearity, , to compensate for the load pressure nonlinearity, or (2) amplifying the servovalve signal at higher levels

1 /


sv sv levels.

Oil Column ResonanceThe effective table mass of the system and the oil column within the actuators defineThe effective table mass of the system and the oil column within the actuators definea mass-spring system with a natural frequency referred to as the oil columnfrequency.

Sketch of Double Ended Actuator

oilk oilk

eqAL L

21

2

eq

oil

AL

fm

::e f fm

Effective bulk modulus of oil

Effective mass of the table

:e qA Piston area2 effm

:L Oil column length

Note that the oil column frequency depends on the effective mass of the “table + specimen”.Oil column frequency of LHPOST under bare condition has been identified at 10.4 Hz.


q y

• Oil column resonance distorts the commanded signal at and around the oil column frequency.

Effects of Oil Column on Fidelity in Signal Reproduction

• On most shaking tables, the oil column frequency falls within the operating range of the system.

• Operation of a shake table at or around the oil column frequency may result in high gain problems.

• Shake table operation at frequencies around 1/3 of oil column frequency will result, due toservovalve load pressure nonlinearity (odd harmonics are excited), in frequency componentsaround the oil column frequency that will cause significant signal distortion.

1940 El Centro Record Part of the Time History FFT of the Cmd and Fbk

250

300Fbk SignalCmd Signal

0.04

0.06Fbk SignalCmd Signal

1940 El Centro Record - Part of the Time History (Bare Table)

FFT of the Cmd and Fbk Signals

150

200

250

|Y(j

)|0

Acc

eler

atio

n [g

]el

erat

ion

[g] Oil Column

Frequency~10.4 Hz

0 5 10 15 20 250

50

100

36 37 38 39 40 41 42-0.08

-0.04

AA

cce


0 5 10 15 20 25Frequency [Hz]

36 37 38 39 40 41 42Time [sec]

Mechanical Sources – Dissipative (friction, viscous) ForcesF i ti i f b f ithi th t lid b i• Friction arises from a number of sources within the system, e.g., slide bearings,mechanical linkages, etc. Specific sources of friction depend on the design andlayout of the shake table system.

• Frictional forces are typically not large, especially in the case of hydrostaticbearings.

• Signal distortion (high frequency) occurs during motion reversals.• The magnitude of friction-induced distortions is approximately constant. Therefore

such distortions are more significant for lower level signals.

Identified Dissipative Force Model for LHPOST (Bare Table)

0.5( ) ( ) ( ) ( )i C l bF t F t C u sign u F sign u ( ) ( ) ( ) ( )viscous Coulomb e x x e xF t F t C u sign u F sign u

Friction Force - Constant(~ 26.0 kN friction coeff. of 0.45%)

Viscous Force (Ce = 44.6 kN(s/m)0.5 )


Effect of Friction on Fidelity in Signal Reproduction

SR-11 Sinusoidal Test ftes t= 1 Hz and Amplitude = 0.769 g

(Bare Table)

1

1.5Fbk SignalCmd Signal High-frequency waveform

distortions at motionreversals due to frictional

0

0.5

lera

tion

[g]

reversals due to frictionalforces. These waveformdistortions may be large.

-1

-0.5Acc

el

5 5.5 6 6.5 7-1.5

Time [sec]


System Mechanical ResonancesWithin any mechanical system, there are numerous resonant frequencies that can be excited,Within any mechanical system, there are numerous resonant frequencies that can be excited,therefore contributing to signal distortion. A good system design philosophy is to keep theseresonant frequencies well beyond (2 to 3 times, Kusner et al., 1992) the maximum operatingfrequency.

2 D Simplified Mechanical Model of LHPOST2-D Simplified Mechanical Model of LHPOST including Specimen

Mechanical resonances

uozu

exist within individual components (local) and within the whole system (global)

Ooxuoy

n B

lock

/ 2ec / 2ec

/ 2k / 2kvbk vbk vbk

( )actWF t ( )actEF tG

1 2

1 2

21 3

ing

Soi

l

eM

(global).

Pedestal

Rea

ctio

n / 2hdk / 2hdk

Sur

roun

d


LHPOST Mechanical Subsystem ResonanceBy numerically integrating the equation of motion of the identified simplifiedBy numerically integrating the equation of motion of the identified simplifiedmechanical subsystem of LHPOST for harmonic excitations over the frequencyrange [0.1-1.3] Hz, we can determine the mechanical subsystem resonant frequency:0.47 Hz (within the operating range).

0.5( ) ( ) ( ) ( ( )) ( )e x e x e x x acteM u t K u t C u t F sign u t F t

449 0 kNSE5

Overview of LHPOST Mechanical Subsystem

PlatenHorizontal Actuator

2.5

3

3.5

49.0 kN66.4 kN100.8 kN250 kNExperimental

SR9

SE4

S

Lateral Bearing 1.5

2

5

Rd

S9

SR7

S4

S6 0 /

steadyx

de

uRF K

Vertical Bearing

Hold-Down Struts

0 0.2 0.4 0.6 0.8 1 1.20

0.5

1

S5 S8

S7S3

0.47


Frequency [Hz]

Resonance Between Pilot Stage and 3rd Stageof Servovalves of LHPOSTof Servovalves of LHPOST

Another mechanical resonance identified in the LHPOST was a resonance betweenthe pilot and 3rd stages of one of the servovalves. This resonance occurred at highfrequency ~250 Hz. It had little effect on reproduced acceleration signals, but infrequency 250 Hz. It had little effect on reproduced acceleration signals, but ingeneral it is important to be aware of such mechanical local resonances.

1971 San Fernando Earthquake - Van Nuys Station FFT of the Fbk Signal

150

200

0 4

0.6

0.8

nt [V

]

Fbk SignalCmd Signal

High frequencyresonance atservovalves

100

|Y(j

)|

0

0.2

0.4

ool D

ispl

acem

en

200 220 240 260 280 3000

50

60 62 64 66 68 70-0.4

-0.2

Sp


Frequency [Hz]Time (sec)

Shake Table – Specimen Interaction• A more difficult source of signal distortion to compensate for is due to specimen

compliance and resulting table - specimen interaction. The reasons are:

Location of the specimen on the platen (e.g., eccentricity-induced torsional motion

of the table-specimen system) will contribute to cross coupling of actuator axes.

M t d i h i i ti t t t l b h i ll b d Most dynamic research on specimens investigates structural behavior well beyond

the elastic range of materials. Therefore, the overall system (table + specimen)

dynamics changes as the specimen enters the plastic range.

In general, shake table tuning is based on the assumption of a fixed (specimen)

coupled mass, since this determines the oil column frequency. With a yielding and

degrading specimen, the oil column frequency is load dependent and time-varying.


Shake Table – Specimen Interaction• The presence of a flexible specimen on a shake table (single or multi-axis) hasThe presence of a flexible specimen on a shake table (single or multi axis) has

significant effect on the frequency characteristics of the overall system: Table-specimen interaction manifests itself in the overall system transfer function as a

resonance/anti-resonance pair (i.e., peak-trough sequence in the system transferp ( , p g q yfunction at the natural frequencies of the fixed-base specimen).

In the case of a yielding and/or degrading MDOF specimen, these peak-troughdistortions of the overall system transfer function are not fixed in time and frequency andcan not be compensated for by using linear fixed-gain controllers, e.g., PID, TVC, andLMRC (linear model reference controllers).

SpecimenSpecimen

Reaction block

SoilPlaten

Actuator

Servovalve

Reaction block

SoilPlaten

Actuator

Servovalve

InputAcc.

OutputAcc. ˆ ( )TotalXFerH j

Estimate

Accumulator Banks

Pump

Pump

Hydraulic Manifold

Blowndown Valves

Hydrostatic bearings

Accumulator Banks

Pump

Pump

Hydraulic Manifold

Blowndown Valves

Hydrostatic bearings

( )TotalXFer j


Banks PumpBlowndown Valves Banks PumpBlowndown Valves

Effect of Table – Specimen Interaction on System Transfer Function

Pre-Sylmar WN Test (3%g RMSA) Post-Sylmar WN Test (3%g RMSA)

Full-scale seven-story R/C shear wall building slice mounted on the LHPOST

1.2

1.5

Total XFer FunctionCoherence Function

Ideal XFer Function1.2

1.5

Total XFer FunctionCoherence Function

Ideal XFer Function

0.9

|H(j

)|

Sylmar EQ 0.9

|H(j

)|

Ideal XFer Function

0.3

0.6

0.3

0.6

Note: During the WN tests, it is assumed that the specimen responds quasi-linearly.

0 5 10 15 20 250

Frequency [Hz]

~1.3 Hz

0 5 10 15 20 250

Frequency [Hz]

~0.9 Hz


g , p p q y

Some Options for “Dealing” with the Effects ofgTable-Specimen Interaction

• Iteratively match the reference (commanded) earthquake record applied at

full-scale without the specimen on the table, then mount the specimen,

and test it with the last iterative earthquake input file.

Drawback: Additional error in earthquake signal reproduction will be

introduced by specimen-table interaction. Unless the specimen is very light

relative to the table platform, signal distortions will be significant.


Some Options for “Dealing” with the Effects ofTable Specimen Interaction

• Iteratively match the reference (commanded) earthquake record scaled

Table-Specimen Interaction

down in amplitude with the specimen on the table, then scale up the drive

signal (from the last iteration) for the actual test. Errors in signal

reproduction resulting from this process are likely to be less severe thanreproduction resulting from this process are likely to be less severe than

in the previous approach.

Drawback: Additional error in signal reproduction will be introduced by the Drawback: Additional error in signal reproduction will be introduced by the

fact that the specimen is behaving quasi-linearly during the signal matching

procedure, but not during the actual test, and further errors will be caused

by non-scalable nonlinearities in the table response itself. Also, the risk of

prematurely damaging the specimen is high.


Signal Distortion Compensation Techniques

MTS 469D Seismic Controller

SYSTEMLINEARITY

PROGRAM

LINEAR NONLINEAR

PROGRAMSHAPE

Used for iteratively matching the reference (commanded)

Amplitude PhaseControl(APC)

AdaptiveHarmonic

Cancellation(AHC)

SINUSOIDAL

the reference (commanded) time history

Iterative techniques can not

Adaptive Online

qcompletely remove the effects of table-specimen interaction. Real time nonlinear adaptive controlInverse

Control(AIC)

Iteration(OLI)

NON-SINUSOIDAL nonlinear adaptive control techniques are required to control evolving nonlinear interaction.


OnLine Iteration (OLI) Technique

Response RMS error versus OLI iteration number for Sylmar record at 0.852-g calibration PGA lit d th d d i fil i h d t th th it ti


PGA amplitude, the converged drive file is reached at the seventh iteration.

Seismic Performance CurvesObjective of SP Curves: Find the required minimum tuning peak accelerationas a function of the target peak acceleration for a given relative RMS error.

Tests Performed on LHPOST to Obtain SP Curves 1940 El Centro Record (Bare Table)

Calibration Amplitude

[g]Target Amplitude (Test Amplitude)

0 07 (20%) 20% 100% 200% 300% 400%0.07 (20%) 20% 100% 200% 300% 400%

0.37 (100%) 20% 100% 200% 300% 400%

0.74 (200%) 20% 100% 200% 300% 400%

1.11 (300%) 20% 100% 200% 300% 400%


Effect of Calibration Amplitude on Signal Reproduction Fidelity

1940 El Centro - Calibrated @20%g PGA - Targeted @300%g PGA (Bare Table)

Reproduction Fidelity

R l ti RMS E 52 5%


Relative RMS Error = 52.5%

Effect of Calibration Amplitude on Signal Reproduction Fidelity

1940 El Centro -Calibrated @300%g PGA - Targeted @300%g PGA (Bare Table)

Reproduction Fidelity

R l ti RMS E 6 9%


Relative RMS Error = 6.9%

Effect of Calibration Amplitude onAchieved Response Spectrap p

Response Spectra for 1940 El Centro Earthquake (Bare Table)Target and obtained 5% damped pseudo-acceleration response spectra

(El Centro earthquake record scaled to 1.11g PGA) ( q g )

2.5

1.5

2

[g]

1

1.5

Sa

Target @1.11g PGA

Calibrated @0.074g PGA

10-1

100

0

0.5

Period [sec]



0.10.2


Period [sec]

Table Seismic Performance Curves

Th l l f lti f0.8 [g]

10%0.8 [g]

10%The level of error resulting frominput scaling is a good measure ofthe error to be expected at othertables using the same controller

0.6

0.8

ccel

erat

ion

RMS Error: 1

0

20%0.6

0.8

ccel

erat

ion

RMS Error: 1

0

20% tables using the same controller.

There is a trade-off betweenincreased fidelity (smaller relative0 2

0.4

on P

eak

Ac

RMS Error: 20

RMS Error: 30%

or: 40%0 2

0.4

on P

eak

Ac

RMS Error: 20

RMS Error: 30%

or: 40% increased fidelity (smaller relativeRMS error) and increased risk ofpremature damage to the specimenby tuning with stronger motions0 2 0 4 0 6 0 8 1 1 2 1 4

0

0.2

Cal

ibra

ti

RMS Error: 40%

RMS Error: 50%

0 2 0 4 0 6 0 8 1 1 2 1 40

0.2

Cal

ibra

ti

RMS Error: 40%

RMS Error: 50%

by tuning with stronger motions.0.2 0.4 0.6 0.8 1 1.2 1.4Target Peak Acceleration [g]

0.2 0.4 0.6 0.8 1 1.2 1.4Target Peak Acceleration [g]


Sylmar Olive View Med 360o recorded during the 1994 Mw 6.7 Northridge earthquake

1

target

g qFull-scale seven-story R/C shear wall building slice mounted on the LHPOST

0.4

0.6

0.8 targettable feedback

0

0.2

a (g

)

0 6

-0.4

-0.2

0 5 10 15 20 25 30-1

-0.8

-0.6


0 5 10 15 20 25 30t (sec)


0.8

1

target


0.4

0.6

table feedback

0

0.2

a (g

)

-0.6

-0.4

-0.2

2 3 4 5 6 7 8 9 10-1

-0.8

t (sec)


t (sec)

NEESNEES--InfillInfill

1

2

on, g

EastWest

-1

0

Acc

eler

atio

Recorded MotionIntended Motion

-22 3 4 5 6

Time, sec

8

100% of Gilroy 3 (1989 Loma Prieta Earthquake)

Shaking direction

45678

eler

atio

n, g

Recorded Motion

Structural period prior to

Structural period after

– Corresponds to the MCE for San Diego for this structure

– Scaled in amplitude by 2.27– Compressed in time by 0.542

0123

0 0 2 0 4 0 6 0 8S

pect

ral A

cc Intended Motion


Compressed in time by 0.542 0 0.2 0.4 0.6 0.8Period, sec

References on Design, Analysis, Characterization, and Modeling of LHPOSTand Modeling of LHPOST

Van Den Einde, L., Restrepo, J., Conte, J. P., Luco, E., Seible, F., Filiatrault, A., Clark, A.,Johnson, A., Gram, M., Kusner, D., and Thoen, B., “Development of the George E. BrownJr. Network for Earthquake Engineering Simulation (NEES) Large High PerformanceOut door Shake Table at the University of California San Diego ” Proc of 13 th WorldOut-door Shake Table at the University of California, San Diego,” Proc. of 13-th WorldConfer-ence on Earthquake Engineering, Vancouver, BC Canada, August 1-6, 2004,Paper No. 3281.

Ozcelik, O., Conte, J. P., and Luco, J. E., “Virtual Model of the UCSD-NEES HighPerfor-mance Outdoor Shake Table,” Proc. of the Fourth World Conference on StructuralControl and Monitoring, San Diego, California, July 11-13, 2006.

Ozcelik, O., Luco, J. E., and Conte, J. P., “Identification of the Mechanical Subsystem of theNEES-UCSD Shake Table by a Least-Squares Approach,” Journal of EngineeringS UCS S a e ab e by a eas Squa es pp oac , Jou a o g ee gMechanics, ASCE, Vol. 134, No. 1, pp. 23-34, 2008.

Ozcelik, O., Luco, J. E., Conte, J. P., Trombetti, T. L., and Restrepo, J., “ExperimentalCharacterization, Modeling and Identification of the NEES-UCSD Shake Table MechanicalSystem ” Earthquake Engineering and Structural Dynamics Vol 37 Issue 2 pp 243 264System, Earthquake Engineering and Structural Dynamics, Vol. 37, Issue 2, pp. 243-264,2008.

Luco, J. E., Ozcelik, O., and Conte, J. P., “Acceleration Tracking Performance of the NEES-UCSD Shake Table,” Journal of Structural Engineering, ASCE, Vol. 136, No. 5, pp. 481-490 2010


490, 2010.

Questions?Questions?


High-flow High-performanceServovalves

3rd stage2nd stage

1st stage

3 stage

4th stage

Courtesy of MTS


Courtesy of MTSSystems Inc.


ThreeThree--Variable Controller (TVC)Variable Controller (TVC)Control ModeControl Mode

Reference

(DisplacementVelocity, Acceleration)

10/Dmax PFk

FeedforwardGains

refx

refx

Reference

(DisplacementVelocity, Acceleration)

10/Dmax PFk

FeedforwardGains

refx

refx

ReferenceSignal

+

+++

10/Vmax

10/Amax AFk

ref

refx

refx

VFk

Ref

eren

ce

Gen

erat

orReference

Signal

+

+++

10/Vmax

10/Amax AFk

ref

refx

refx

VFk

Ref

eren

ce

Gen

erat

or

DisplacementFbk

+- +

++-+

10/Amax

10/Dmax

Notch Filter

Qty = 5

JFk

Pk MkFeedback

Gains

MasterGain

ref

fbkx

Controller Output

to Servovalves

ck

or

DisplacementFbk

+- +

++-+

10/Amax

10/Dmax

Notch Filter

Qty = 5

JFk

Pk MkFeedback

Gains

MasterGain

ref

fbkx

Controller Output

to Servovalves

ck

or

AccelerationFbk

++

+10/Vmax

10/Amax

Notch Filter

Ak

Vk Ik 1/ s

Reset Integrator

fbkx

fbkx

F

Feed

bac

Gen

erat

o

AccelerationFbk

++

+10/Vmax

10/Amax

Notch Filter

Ak

Vk Ik 1/ s

Reset Integrator

fbkx

fbkx

F

Feed

bac

Gen

erat

o

ForceFbk

Lowpass Filter

10/Fmax

Highpass Filter

DPkfbkFForceFbk

Lowpass Filter

10/Fmax

Highpass Filter

DPkfbkF

TVC is a displacement controller with sophisticated feed-forward gains.

Courtesy of MTSSystems Inc.


TVC is a displacement controller with sophisticated feed forward gains.

Some Options for “Dealing” with the Effects ofTable-Specimen Interaction

• Mount the specimen on the table, but restrain it as much as possible so

that it can not move relative to the table platform (accomplished by

Table-Specimen Interaction

that it can not move relative to the table platform (accomplished by

adding extra bracing, etc.), and iteratively match the reference

(commanded) time history applied at full scale. The benefit of this( ) y

approach is that the overturning moment due to the high center of gravity

of the specimen is compensated for in the signal matching procedure.

Drawback: It may be unacceptable to run several pre-tests as some

degradation of the model may occur. The shaking table user must

therefore make a judgement as to whether the accuracy of table motion is

more important than the integrity of the specimen for the final test(s).


NEESNEES--InfillInfill

1

2

on, g

EastWest

-1

0

Acc

eler

atio

Recorded MotionIntended Motion

-22 3 4 5 6

Time, sec

8

100% of Gilroy 3 (1989 Loma Prieta Earthquake)

Shaking direction

45678

eler

atio

n, g

Recorded Motion

Structural period prior to

Structural period after

– Corresponds to the MCE for San Diego for this structure

– Scaled in amplitude by 2.27– Compressed in time by 0.542

0123

0 0 2 0 4 0 6 0 8S

pect

ral A

cc Intended Motion


Compressed in time by 0.542 0 0.2 0.4 0.6 0.8Period, sec

TableTable--Specimen Interaction (?)Specimen Interaction (?)

S D

0.04

0.05

e

Longitudinal (E-W)Vertical

Longitudinal (E-W)V ti l

Longitudinal (E-W)V ti l

Undamaged Structure Some Damage Severe Damage

0.01

0.02

0.03

Four

ier A

mpl

itude Vertical Vertical Vertical

00 10 20 30 40

Frequency, Hz0 10 20 30 40

Frequency, Hz0 10 20 30 40

Frequency, Hz

Shake Table Training Workshop 2010 – San Diego, CA43


1

target

g qFull-scale seven-story R/C shear wall building slice mounted on the LHPOST

0.4

0.6

0.8 targettable feedback

0

0.2

a (g

)

0 6

-0.4

-0.2

0 5 10 15 20 25 30-1

-0.8

-0.6


0 5 10 15 20 25 30t (sec)


0.8

1

target


0.4

0.6

table feedback

0

0.2

a (g

)

-0.6

-0.4

-0.2

2 3 4 5 6 7 8 9 10-1

-0.8

t (sec)


t (sec)

Relative RMS Error as a Function of Target PGA for Given Calibration PGAfor Given Calibration PGA

Relative RMS error versus target or test PGA curves for (a) Sylmar; (b) El Centro earthquake records (AIC training was performed under 7%-g RMS WN acceleration); and (c) El Centro earthquake record earlier AIC training was performed under 10%-g RMS WN acceleration.


Table Performance Curves

Th l l f lti fThe level of error resulting frominput scaling is a good measure ofthe error to be expected at othertables using the same controllertables using the same controller.

There is a trade-off betweenincreased fidelity (smaller relativeincreased fidelity (smaller relativeRMS error) and increased risk ofpremature damage to the specimenby tuning with stronger motionsby tuning with stronger motions.


LHPOST Performance Specifications

• Size: 12.2 m x 7.6 m• Vertical Payload: 20 MNy• Frequency Bandwidth: 0-20 Hz• Phase 1: Uniaxial System:

– Stroke: 0.75 m; Velocity: 1.8 m/sec; Acceleration: 3.0g• Phase 2: Triaxial System:

Direction Acceleration Velocity Displacement Horizontal-X g3 m/s1.8 m0.75 Horizontal-Y g1.5 m/s0.9 m0.375

V i l 1 0 /0 0 1 0Vertical g1.0 m/s0.5 m0.150


George E. Brown, Jr. Network for Earthquake Engineering Simulation, NEES-2

Performance SpecificationsPerformance Specifications Size: 12.2 m x 7.6 m

V ti l P l d 20 MN Vertical Payload: 20 MN Frequency Bandwidth: 0-20 Hz Phase 1: Uniaxial System: Phase 1: Uniaxial System: Stroke: + 0.75 m; Velocity: + 1.8 m/sec; Acceleration: + 3g

Phase 2: Triaxial System:Phase 2: Triaxial System:Direction Acceleration Velocity Displacement

Horizontal-X g3 m/s1.8 m0.75 Horizontal-Y g1.5 m/s0.9 m0.375

Vertical g1.0 m/s0.5 m0.150

UCSDUCSD

Documents

Shake Table Control Fidelity in Signal ...nees.ucsd.edu/eot/docs/2010-user-perspective-seismic-testing/UCSD... · Fidelity in Signal ReproductionFidelity in Signal Reproduction &