JRC35934 Consolidar

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the Citizen

Mission of ELSA

To provide research and contribute to European Standards for risk mitigation in construction through integrated use of experimental testing and numerical modeling in Structural

Mechanics

General view of ELSA

Seville Spain• Institute for Prospective

Technological Studies

Brussels Belgium• General Directorate

Geel Belgium• Institute for Reference Materials

and Measurements

Petten The Netherlands• Institute for Advanced

Materials

Karlsruhe Germany• Institute for Transuranium

Elements

Ispra Italy• Institute for the Protection and

Security of the Citizen• Institute for Environment and

sustainability• Institute for Health and

Consumer Protection

The sites of JRC in Europe

(European Laboratory for Structural Assessment)

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Institute for the Protection and Security of the Citizen

The EUROCODES

• To improve the assessment of structures• The basement for an unique European Standard in civil

engineeringMain topic of ELSA Laboratory

To verify the proposed codes by means of:

Experimental testing at real scale

Computer Simulation

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The two methods for Earthquakes Simulation

ShakingTable

Reaction Wall (PSD methods)

Reduced Scale models

Real Time test

Real scale models (failure criteria are available because of the same size as real)

Expended Time Test

ELSA

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenELSA Experimental Activities

Seismic Assessment of Civil StructuresAll PSD methods or Cyclic testing (linear and un-linear testing)

- Research for structural vulnerability assessment of civil structures under earthquakes

-Strengthening/repair techniques for civil and cultural heritage structures.

- Tests on Components

Structural Response ControlCyclic or PSD (un-linear testing)

Passive Control: Base isolation, energy dissipation devices.(metallic yield, friction, visco-elastic dampers, tuned mass, tuned liquid dampers)

-Semi-Active Control Variable-friction, variable-orifice,controllable-fluid dampers (ER/MR), controllable tuned liquid dampers.

- Active Control (Cable Stayed Bridges…)

Structural Identification and Monitoring-Experimental Modal Analysis (elastic testing)

-Fatigue testing (elastic to rupture testing)

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Quasi-static testingCyclic testing

Conventional PsD testingon full-scale models

Continuous PsD (CPsD) testing

PsD testing with substructuring

Fast on-line testing with substructuring (fast hybrid testing)

CPsD with substructuring

CPsD with Non-lineareSubstructuring

ELSA Experimental Activities

Fatigue testing

Cyclic testing

Methods Development

Dynamic testing

Shaker, HammerSnap Back

Ambient Monitoring

Hybrid (experimental + numeric) Experimental

1990

2006

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The ELSA Reaction Wall: tool to The ELSA Reaction Wall: tool to realiserealise the PSD or cyclic the PSD or cyclic TestingTesting

16m

4.2m

25m4m5m

20m

13m

20m

Anchor holes 1m spacing m

Bending moment 200 MNm


Base Shear 20 MN

16m

4.2m

25m4m5m

20m

13m

20m

Anchor holes 1m spacing m






Base Shear 20 MN

Base Shear 20 MN

Servo hydraulic dynamic actuators Servo hydraulic static actuators8x 1.0 MN 1.0m 4x 3.0 MN 0.5m

12x 0.5 MN 1.0 / 0.5m 8x 0.8 MN 0.5m4x 0.2 MN 0.2 m

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Cyclic testing: (experimental method)• Inertial and velocity dependence forces are not considered.

• The actuators could be controlled in displacement or in force.

Example Results

-70

-50

-30

-10

10

30

50

70

-15 -10 -5 0 5 10 15 20

EXP: SW3 cyclic test

NUM: cyclic test

NUM: monotonic test

huδ

vu1δ vu2δ1V 2V

H

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Short History of the Short History of the PsDPsD MethodMethod

1969: Hakuna, Shidawara & Hara formulated the initial concept of PsD testing in Japan. They analyzed a 1-dof system (cantilever steel plate) using an electromagnetic actuator controlled by an analog computer.

1974: Takanashi & Nakashima were the first in obtaining satisfactory system response.

By the mid 80’s PsD testing was being carried out on a significant scale in Japan. In Tsukuba a 26m height RW has been used to test full-scale seven story buildings.

1986: Shing, Mahin… introduced and developed the PsD methodology in USA.

1991: European Laboratory for Structural Assessment ELSA is constructed at Ispra

Later on, new centres developed including Taiwan 1999, Korea 1999, Italy (Trento2002), … as well as a number of smaller laboratories (UK Oxford 1999…).

1996: Continuous PsD testing was developed at JRC-Ispra

Following the research carried out the last 25 years, and in particular numerous comparisons with shaking table tests, the PsD method is now generally recognized as a reliable method for testing many types of dynamic systems.

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∫ dt... )(tx

Servo-HydraulicActuators

DisplacementTransducers

Reference Frame

( ( ) )) ( gR tMa t Cv t MIx+ + = −

Measured Restoring Force )(tR

gx

Imposed Displacement )(tx

Accelerogram

ForceTransducers

PSEUDO-DYNAMIC METHOD

-Calculated terms

-Measured or Numerical term

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PSD Testing: solving the equationPSD Testing: solving the equation

(( ) ( ) ( )) gR tMa t Cv t MIx t+ + = −

The structure is discretised in n DoF (space discretisation)

The motion is discretised in time steps ∆t

M and C are matrix of n DoF, supposed diagonal.

Inertial Forces …………………. Calculated at each step ∆t( )Ma t =( )Cv t = Velocity Dependent Forces (Viscous) Calculated at each step ∆t

( )R t = Reaction Forces (= -K.d) Measured at each step ∆t

( )gMIx t = External Forces Input red in a file sampled at ∆t

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Read Input Excitation2

1 2n n n ntd d t v a+

∆= + ∆ ⋅ + ⋅

1nf +

Compute the displacement to apply

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1 1( ) ( )2 2n n nn nt ta M C f CvR C a−

+ + +

∆ ∆= + ⋅ ⋅ − − − ⋅ ⋅ Compute acceleration

1 1( )2n n n ntv v a a+ +

∆= + ⋅ + Compute velocity

PSD Testing: solving the equationPSD Testing: solving the equation

1 1 1 1n n n nMa v fRC+ + + ++ + =The step n realised, the new step n+1 is computed with the discrete

equations deduced from the explicit Newmark method:

Apply the displacement:t∆

The structure is moving of one time

step:

1nd +

Read the Reaction force:

1nR +

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenThe Conventional The Conventional PsDPsD Method:Method:

(Asynchronous Loading)(Asynchronous Loading)

Ground Acceleration

Earthquake Time Scale

∆T

PsD Time Scale

PsD Steps Description

Hold Period

Hold PeriodRamp Period

Stabilization Period (100 to 200 ms)Measurement Period (40 to 120 ms)Communication and computation period (400 to 800 ms)

Step n Step n+1

PsDT∆

dn+1

dn

Begin: Compute the ext. load force: fn

Measure the restoring force: rn

Compute an and vn

Compute displ. response: dn+1

Impose dn+1 on the test structureIncrement nWait end of ramp period Go to Begin

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Advantages and DrawbacksAdvantages and Drawbacks

Tests normally run on an Expanded Time-Scale of the order of 100 time (or more) the actual time-scale

Advantages:

. It makes full scale testing feasible.• It simplifies the equipment needed.• It allows for inspection of the structure between load steps.• The servo-control and the measurements are performed with high

accuracy. • The tests can be stopped at any moment (further inspection, new

instrumentation, “collapse loading”)

Drawbacks:

• Any strain rate effects in the test specimen is not included. • Suffers of stress relaxation effects during the Hold Periods.

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Advantages and DrawbacksAdvantages and Drawbacks

Advantages:

• Reproduce perfectly the excitation accelerogram.• Easy on-line verification of the test quality by checking energy

balance equations and identification of modal dampings.• This hybrid method is appropriate to incorporate substructuring

testing.• Allow multiple distributed PsD tests, eventually in laboratories

geographically separated. Appropriate for Tele-operating.• Allow biaxial tests (3-Dof per floor including rotation).

Further Drawbacks:

• The method includes various approximations in its algorithm:

• Space discretization: The test structure is assumed as aspring-mass discrete system (limited number of Dofs).

• High sensitivity to measurement and control errors.• Motion equations solved by Explicit algorithm => integration time step limitation.

• Difficulty to control vertical motion

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenThe conventional The conventional PsDPsD methodmethod

An ExampleAn Example

Bi-axial PsD test of a 3-storey torsionally unbalanced RC structure

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenThe Continuous The Continuous PsDPsD MethodMethod

(Synchronous Loading)(Synchronous Loading)

PsD Time Scale

Ground Acceleration

Earthquake Time Scale

Structural displacement

Step n

Step n+1

The time scale expansion factor: λ = N * ∆t / ∆T

∆T

∆t

N interpolated values Control loop:Compute the external load force: fn

Measure the restoring force: rnCompute an and vn

Compute displ. response: dn+1

Impose dn+1 on the test structure:

… Control Algorithm:Controller target = dn+1(sampling time∆t ≈ 2 ms)

Go to Control loop

dn+1

dn

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenThe Continuous The Continuous PsDPsD Method:Method:

AdvantagesAdvantagesAvoid hold periods and structural relaxation

• Enable very accurate PsD tests (signal/noise ratio improvement)

• Extend PsD testing capabilitiesto some strain rate sensitive devices/componentsto fast tests with substructuring

Smooth and accelerate the testsReduce the errors

BUT …! Require a completely new implementation

-in hardware: master and slave controllers-in software: time scale introduction in control algoritms

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenThe Continuous The Continuous PsDPsD Method: Method:

Assessment of Large Scale StructuresAssessment of Large Scale StructuresStrengthening/repair

and rehabilitation

Preservation of monuments

Construction norms(Eurocodes)

Anti-seismicIsolation

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Wet lay-up application of a quasi-isotropic carbon FRP on the shear walls of a reinforced concrete dual frame

The Continuous The Continuous PsDPsD Method: Method: Assessment of Assessment of Strengthening/repair techniques ofStrengthening/repair techniques of Large Large

Scale StructuresScale Structures

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Base isolated steel frame

Seismic Test

Characterisation and Snap-Back

High Damping Rubber Bearing

ContinuousContinuous PsDPsD TestingTestingBase Base isolationisolation

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Institute for the Protection and Security of the CitizenContinuousContinuous PsDPsD TestingTesting: :

Passive Passive EnergyEnergy DissipationDissipation DevicesDevices (HDR)(HDR)

PROTECTED CONCRETE FRAME

Designed for non seismic areaand upgraded with retrofitting

• 2 bays of 5 m• 4 m transverse direction• 2 storeys of 2.67 m

Viscoelastic damper

Steel flange

CenterPlate

RC Frame protected with Rubber Dampers installed in K-bracing

Rubber

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Effect of the Strain Rate on the Load-Displacement

characterisation curve

Characterisation curve corrected against the Strain Rate effects

ContinuousContinuous PsDPsD TestingTestingPassive Passive EnergyEnergy DissipationDissipation DevicesDevices(HDR)(HDR)

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Elevation of the Steel frame structureprotected with dissipative braces

ContinuousContinuous PsDPsD TestingTesting: : Passive Passive EnergyEnergy DissipationDissipation DevicesDevices ((JarretJarret))

Application of Jarret devicesThe viscosity and the compressibility (15% at 400 MPa) of these fluids allow a single device to function as a shock absorber and a spring making unnecessary any auxiliary stroke return mechanism.

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenContinuousContinuous PsDPsD TestingTesting: :

Passive Passive EnergyEnergy DissipationDissipation DevicesDevices((JarretJarret))

Displacement (mm)

For

ce (k

N)

λ = 1

λ = 300

λ = 300corrected

Force-displacement cycles at reference speed (solid), 300 times slower (dashed) and 300 times slower after correction (dash-dot line). Sinus displacement

300 300 1corr meas meas

of B f A fλ λ λ= = == + ≈

300 300 1corr meas meas

of B f A fλ λ λ= = == + ≈

1.184 0.48 kNoB A= = −

Time scale correction on Jarret devices characterisation

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0 2 4 6 8 10 12 14 16 18−30

−20

−10

0

10

20

30

40

Time (sec)

I−S

drift

Dis

pla

ce

me

nt

1st

flo

or

(mm

) struttura non protettastruttura protetta con i Jarret

0 2 4 6 8 10 12 14 16 18−40

−30

−20

−10

0

10

20

30

40

Time (sec)

I−S

drift

Dis

pla

ce

me

nt

2n

d f

loo

r (m

m) struttura non protetta

struttura protetta con i Jarret

0 2 4 6 8 10 12 14 16 18−30

−20

−10

0

10

20

30

40

Time (sec)

I−S

drift

Dis

pla

ce

me

nt

3rd

flo

or

(mm

) struttura non protettastruttura protetta con i Jarret

Energia di input

Energia assorbita totale

Energia assorbita dalla struttura

Energia Cinetica

0 2 4 6 8 10 12 14 16 18−1

0

1

2

3

4

5

6

7x 10

4

000# Time (s)

Tot

al E

nerg

y (J

)

Floor 1

Floor 2

Floor 3

ContinuousContinuous PsDPsD TestingTesting

ExampleExample withwith JarretJarret devicesdevices

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Developed in ELSA for the ISTECH projectInnovative Stability Techniques for the European Cultural Heritage

Main tasks of ELSA:- Characterization of SMAs samples for engineering purpose

- Full-scale Pseudo-Dynamic (PsD) tests on unprotected and protected masonry walls

ContinuousContinuous PsDPsD TestingTesting: : Passive Passive EnergyEnergy DissipationDissipation DevicesDevices

(SMA (SMA devicesdevices))SMA = Shape Memory Alloys

Phase Changes in the SMA Crystals

Cooling or

Stress increase

Heating or

unloading

(deformed)

lengthening

εε

Phase Transformation in the AlloyPhase Transformation in the Alloy

StressStress TemperatureTemperature

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The ISTECH project: Characterization of SMAs

ContinuousContinuous PsDPsD TestingTesting: : Passive Passive EnergyEnergy DissipationDissipation DevicesDevices(SMA)(SMA)

Typical and ideal behaviour of a sample of SMA during a test performed

in ELSA

Super-Elastic Effect : Small residual strain.

Hysteresis effect : Large amount of energy dissipation.

Safeguard of material : High and constant stress.The 3 advantageous The 3 advantageous

effects of SMA for effects of SMA for seismic protection.seismic protection.

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Experimental dataExperimental data

nCdcm BeAE .−+=

Energy dissipation with respect cycle number


ContinuousContinuous PsDPsD TestingTesting: : Passive Passive EnergyEnergy DissipationDissipation DevicesDevices(SMA)(SMA)

StressStress--Strain for 4 frequenciesStrain for 4 frequencies

0.01 Hz0.01 Hz

5 Hz5 Hz

1 Hz1 Hz0.1 Hz0.1 Hz

5 Hz5 Hz

0.01 Hz0.01 Hz

-NiTi samples with small diameters showed a better energy dissipation

-The σ-ε curve become stable after 20 cycles assuring a good dissipation

-The SMAs behavior is sensitive to frequency (tests done up-to 5 Hz)

cycle 100

5 Hz.

Task 4

Improvement of the dynamic behaviour

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The masonry wall and its numerical model

Homogeneous modelHomogeneous model

ContinuousContinuous PsDPsD TestingTesting: : Passive Passive EnergyEnergy DissipationDissipation DevicesDevices ((SMAdSMAd))

The ISTECH Project: Retrofitting of damaged masonry wall with SMA Devices

SMA devices

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The ISTECH Project: Full-scale PsD tests of masonry walls

• The devices dissipated about 30% of the total input energy of the system

• The protected wall allowed earthquake intensities 60% greater than the bare wall for the same final typology of damage

ContinuousContinuous PsDPsD TestingTesting: : Passive Passive EnergyEnergy DissipationDissipation DevicesDevices (SMA)(SMA)

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Institute for the Protection and Security of the CitizenSMA devices applicationsSMA devices applications

Basilica of SanBasilica of San--Francesco in AssisiFrancesco in AssisiSouth Tympanum and SMAD devicesSouth Tympanum and SMAD devices

TrignanoTrignano S.Giorgio Church Bell S.Giorgio Church Bell TowerTower. Local damage and . Local damage and

reinforcement adoptedreinforcement adopted

ISTECH Application

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Institute for the Protection and Security of the CitizenInstitute for the Protection and Security of the CitizenPsDPsD Testing with Testing with SubstructuringSubstructuring

Piers testedphysically by PSD

method

Measure of the Reaction forces on the piers

- Critical parts are tested- The remaining structure is computed- Both are coupled through Pseudo-Dynamic

numerical model

Deck modeledanalytically by

F.E.M.

Application for testing of bridges1 1 1 1n n n nMa v fRC+ + + ++ + =

R1

Ri

0

…

0

0

K.d

…

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The Conventional PsD Algorithm with Substructuring

Numerical

part

d(n), v(n), a(n)

Experimental

part

1 3

4

2

d(n+1), v(n+1), a(n+1)

The displacement increment is imposed by means of a ramp followed by an hold period==> Asynchronous process and large control step (≈2s)

THEN==> Easy implementation of non-linear substructuring (time for convergence, no synchronization)

BUT==> Relaxation in the experimental structure and difficulties in handling the strain rate dependency

The conventional staggered procedure:

∆T

PsDPsD Testing with Testing with SubstructuringSubstructuring

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AB-W AB-G

Schematic representation

P1(A20)

WIEN GRAZ

62.00 m 62.00 m67.00 m 67.00 m 67.00 m 67.00 m 67.00 m

P2(A30) P3(A40) P4(A50) P5(A60)

P6(A70)

The real bridge…

The VAB Project Application to the Warth Bridge, Austria

Physical piers in the lab.

Numerical model for the deck and piles A20 A30 A50 A60

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Pier A50 Pier A60

Pier A40

Pier A70

Pier A30

Pier A20

Experimental piers

Analytical piers: behaviour with easier modelling than experimental ones

The application of the vertical load

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Isolated Bridges: Isolation/Dissipation (I/D) devices

P3

P2P1

B213A-PI(Partial isolation)

P

F

Dissipating part (Spindle)Sliding supports Spindle: Inelastic Devices: to be removed after hard events

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Isolated Bridges: Isolation/Dissipation (I/D) devicesPsDPsD Testing with Testing with SubstructuringSubstructuring

-2.0 .0 6.0X1.E-2

-10.0

.0

10.0X1.E-2

-4.0 .0 4.0X1.E-2

-8.0

.0

10.0X1.E-2

-3.0 .0 6.0X1.E-2

-.15

.00

.15

-3.0 .0 6.0X1.E-2

-.20

.00

.25

-4.0 .0 5.0X1.E-2

-.20

.00

.20Force [MN] Force [MN] Force [MN]

Force [MN]Force [MN]

‘Full’ Isolation (All Deck Supports Isolated): Action 1.0xDE

Disp. Disp. Disp.

Disp. Disp.

At the top of the piers

At the top of the isolators

Results on the example of full isolation of the deck

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Extension to Fast on-line Substructuring tests on Components made of materials exhibiting velocity dependant behaviour.

Seismic Isolation

Energy Dissipation

F1F2

< Drift displ.> Force

Vert. Load 1 Vert. Load 2

< Displ.> Force

SEISMIC ISOLATIONElastomeric BearingsLead Rubber Bearings

PASSIVE ENERGY DISSIPATIONDampers installed in K-bracingDiagonal bracingViscoelastic damperFriction dampersViscous Fluid dampersMetallic Yield dampersSmart Material: SMA…

SEMIACTIVE CONTROL:Variable-orifice fluid dampersControllable friction devicesvariable stiffness devicesControllable fluid dampers

Continuous Continuous PsDPsD Testing with Testing with SubstructuringSubstructuring

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d(n), v(n), a(n) d(n+1), v(n+1), a(n+1)

Suppression of the hold period==> Synchronous process and very small control step (1 or 2 ms)==> simplest and most accurate PsD algorithm (CD scheme)

THEN==> No relaxation==> Faster test==> Improvement of the quality of the results

BUT==> Difficulties in the implementation of non-linear substructuring==> Implementation of a new substructuring strategy

The basic inter-field procedure

Numerical

part

Experimental

part


Step running schema

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The Oxford Test Set-up

Athens Shaking table test

Fast Continuous Fast Continuous PsDPsD Testing with Testing with SubstructuringSubstructuringProject NEFOREEE

Steel box dissipative device

Jarret fluid dissipative device

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Vertical load cell

Air cushion

Displacement transducer

Isolators

Actuator load cell

Actuator

Experimental Set-up:Rubber bearing characterization / substructuring set-up

Collaboration/NetworkBoulder University (USA)

Trento University (I)

Bristol University (UK)

Oxford University (UK)

Patras University (Gr)

Rostock University (G)

Rubber bearing isolation devices


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Experimental Set-up: Teflon / Jarret - Visco-Elastic Shock Absorbers/ substructuring set-up

Isolator + absorber device : Jarret / Teflon devices


ATTUATORI VERTICALI

2 JARRET IN PUSH-PULL

ATTUATORE ORIZZONTALE

CONTROPIASTRA PER L' ALLOGGIO DEL TEFLON

DISCO DI TEFLON

PIASTRA IN ACCIAIO LUCIDATO

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Dispass ELSA [TEFLON ONLY DECK] (82: Controller Generated)

d142

d147

d153

d159

0 200 400 600 800 1000 1200-0.1

-0.05

0

0.05

0.1

0.15

Sampling Point

002#

Fric

tion

Coe

ff - (

-)



µ decreases as the vertical load increases

Test at constant speed with different vertical loads: d142 (= 0t), d147 (= 8t),d153 (=20t), d159 (= 28t)

Dispass ELSA [TEFLON & 2 NEW JARRET] (80: Controller Measured)

d196

d197

d198

d199

-15 -10 -5 0 5 10 15-50

-40

-30

-20

-10

0

10

20

30

40

50

003# Haidenhein Displacement (mm)

004#

Loa

d C

ell F

orce

(kN

)

Tests at different speeds and constantmaximium load: λ = 1 (in blue), λ = 3 (in red), λ = 5 (in green), λ = 30 (in black)

Dispass ELSA (80: Controller Measured)

[TEFLON & 2 NEW JARRET] d196

[TEFLON ONLY DECK] d159

-15 -10 -5 0 5 10 15-50

-40

-30

-20

-10

0

10

20

30

40

50


004#

Loa

d C

ell F

orce

(kN

)

Comparison between the teflon dissipation (in red) and the teflon + Jarret (in blu) in the test with λ = 1 and with vertical load = 28t

Jarret / Teflon devicesHigh speed CPsd: λ = 1 to 30

44



Dispass ELSA [TEFLON & 2 NEW JARRET] (80: Controller Measured)

d196

d199

d199 corrected

-15 -10 -5 0 5 10 15-40

-30

-20

-10

0

10

20

30

40


004#

Loa

d C

ell F

orce

(kN

)

Comparison between the force-displacementlow-speed cycle (in red), in the low speedcorrected test (in green) and in the high speedtest (in blue)

Fast CPsD Test with Substructuring:Jarret / Teflon devices

Dispass ELSA [Substructuring BabyFrame] (62: PsD Algorithm Generated)d284: test PsD algorythm (new tef-jar; 100000 pti,old corr)08/04/04

Level 1001#

Level 2002#

Level 3003#

Level 4004#

0 1 2 3 4 5 6 7-10

-5

0

5

10

15

20

000# Time (s)

I-S D

rift D

ispl

acem

ent (

mm

)

Interstorey drift: Protected structure Non protected structure

Dispass ELSA [Steel Unprotected Frame] (62: PsD Algorithm Generated)d35: 100% EARTHQ. (m=8.96 8.96 8.88) 03/04/02

Level 1001#

Level 2002#

Level 3003#

0 1 2 3 4 5 6 7 8-30

-20

-10

0

10

20

30

000# Time (s)

I-S D

rift D

ispl

acem

ent (

mm

)

30 30 0 1corr meas measf Bf A fλ λ λ= = == + ≈

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45


Real structure

Hysteretic Device System


Example of Passive Friction devices

numerical substructure

CPsD test on the device

46


Laboratory setup

Fast CPsD Test with Substructuring


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47


Semi-active control of bridges based on controllable friction devices (CFDs)


RESULT

for a constant pressure

Dissipative cycles

Real Time testing without SAC

48


• The analytical part is advanced with a large time step ∆t, using at each new step level d(t), v(t), a(t) of the connection points obtained through the experimental process at the end of the previous large step.• The experimental part uses at each sub-cycle level δt, as an additional external force, what was generated in the analytical part at the end of the previous large time step.

==> Drawback: the force coming from the analytical structure is not well synchronised with the external loading of the experimental part which is updated at the end of each subcycle (this delay is known to introduce damping).

Simple inter-field procedure.

Analytical

part

Experimental

part

tn tn+1 tn+2

tn+m/M

Computation

r(t)-

d(t), v(t), a(t)

∆t

Continuous PsD Algorithm with Non-lineare Substructuring


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49


• Basically the analytical structure is integrated with a time step ∆T and 2∆T . This allows to know the location of the analytical structure one large time step ∆T in advance with respect to the experimental structure.• It is thus possible to drive the experimental structure with more updated information than with the basic scheme.Ref: Continuous PsD testing with non-linear substructuring: P. Pegon and G. Magonette

Experimental

part

tn tn+1 tn+2

tn+m/M

Analytical

part

IntegrationTime: ∆T

IntegrationTime: 2∆T

2 ms

)()()(

n

n

n

tatvtd

)()()(

1

1

1

+

+

+

n

n

n

tatvtd

)()()(

2

2

2

+

+

+

n

n

n

tatvtd

)()(1+n

n

tftf

)()(

2

1

+

+

n

n

tftf

Improved inter-field procedure.

∆T

Continuous PsD Algorithm with Non-lineare Substructuring


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Institute for the Protection and Security of the CitizenDynamic reference test for the PSD methods

Snap Back testsDynamic Snap-back test

Oscillation of NEFOREEE structure by screw rupture

Modal measurement by Logaritmic decrement (1DoF)

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Institute for the Protection and Security of the CitizenDynamic reference test for the PSD methods

Snap Back tests

Signal

Frequency

Damping

Comparaison between PSD Snap-Back and Dynamic Snap-back test

0.5440.5780.508Damping (%)

-2.5362.54Frequency (Hz)

Exponential fitting

(time method)

Fourier transform

(Frequency method)

Log.Decrement(cyclesmean)

(time method)

NEFOREEE BARE FRAME: Results for the first mode of bending in X direction on central acceleration

( ) ( ) 0( )Ma t Cv t R t+ + = PSD snap-back equation

Dynamic results

52

Institute for the Protection and Security of the CitizenDynamic reference test for structural evaluation

Hammer Test Evaluation of the efficiency of the retroffiting of masonry walls in In-Plane and

Out-Plane direction by frequency shift and comparaison with Cyclic test

10 15 20 25

10

20

30

40

50

60

70

80

90

In plane frequency shift after reinforcement

Frequency [Hz]

FREQ

RES

P [A

mp.

]

Glass

Steel

Carbon

A=6y- F=6y [A]m029234

A=15y- F=15y [A]mr029007

A=6y- F=6y [A]m039313

A=6y- F=6y [A]mr039050

A=4y- F=6y [A]m049016

A=5y- F=6y [A]mr049072

40 60 80 100 0

10 20 30 40 50 60 70 80

Out of plane frequency shift after reinforcement

X= 57.5Y= -12Z= 170

Frequency [Hz]

FRE

QR

ES

P [A

mp.

]

Glass

Steel

Carbon

Details of reinforcement made on brick walls with carbon fibres on left and mortar with glass fibres or steel fibres on right.

- 1 5 0

- 1 0 0

- 5 0

0

5 0

1 0 0

1 5 0

- 3 0 - 2 0 -1 0 0 1 0 2 0 3 0

h o r iz o n ta l d is p la c e m e n t [m m ]

horiz

onta

l loa

d [k

N]

W a ll n o .5 V IR G IN W a l l n o .4 R E IN F s te e l f ib e r sW a l l n o .3 R E IN F g la s s f ib e rs

Cyclic InPlaneTests

27

53


A=6y- F=6ym069103

UNDAMAGED WALL

A=6y- F=6y md069001 DAMAGED

WALL

0 20 40 60 80 1000

50

100

150

Wall no:6 supported

Frequency [Hz]

FREQ

RE

SP [A

mp.

]

integro

danneggiato

Dynamic reference test for structural evaluation

Hammer Test : monitoring the damage

One of the main advantage of the PSD method is to stop the test on the structures at different loading level.

Then the hammer test enables to check, by dynamic impulse, the correspondant levels of damage which

could be measured on a real structure .

A=4x- F=0Ax mr049056

A=4x- F=2Ax mr049058

A=4x- F=4Ax mr049060

A=4x- F=6Ax mr049062

A=4x- F=8Ax mr049064

A=4x- F=10Ax mr049066

A=4x- F=12Ax mr049068

0 50 100 150 200 -600

-500

-400

-300

-200

-100

0

100

200

mr04: Brick Wall 4 reinforced-supported

X= 0 Y= 0 Z= 158

Frequency [Hz]

FRE

QR

ESP

[Am

p.]

mrd041421

mrd041423

mrd041425

mrd041427

mrd041429

mrd041431

mrd041433

0 50 100 150 200 -1000

-800

-600

-400

-200

0

200

mrd04:Brick Wall 4 reinforced supported damaged

Frequency [Hz]

FRE

QR

ESP

(Pha

se)

0Ax

2Ax

4Ax

6Ax

8Ax

10Ax

11Ax

Unwrapped Phase change

Frequency changeNew Wall

Damaged Wall

54


mN

lkff kks ⋅⋅

==2

2

12kk N kf

l mπξ

⎛ ⎞= ⋅ ⋅ + ⎜ ⎟⋅ ⎝ ⎠

Dynamic method: Ambient Monitoring of cables In ELSA

Frequency Hz

Damping %

2.40754.81297.19188.58309.6247

12.023114.374916.876919.227721.734924.201026.656929.158831.708334.2533

2.10450.45740.53200.58210.40930.38900.17320.22020.28210.24640.16200.23210.40010.15250.1207

Natural Vibrations of one cable measured by spectral average

High order number of modes measurements enable to find the boundary conditions of the cable:

2 2

2

2 1(1 (4 ) )2 2kk N kfl m

πξ ξ

= ⋅ ⋅ + + + ⋅

-Pinned without stiffness

-Pinned with stiffness

-Fixed with stiffness

2

12kk N kf

l mπξ

⎛ ⎞= ⋅ ⋅ + ⎜ ⎟⋅ ⎝ ⎠

mN

lkff kks ⋅⋅

==2 Nl

EIξ = ⋅

28

55


VARIATION OF FREQUENCIES WITH INCLINATION

0.975

0.98

0.985

0.99

0.995

1

1.005

78.6 70 60 50 40 30 0

DEGREES OF INCLINATION

NO

RM

ALI

SED

VA

LUES

MODE 1MODE 2MODE 3MODE 5MODE 6MODE 7MODE 8MODE 9MODE 10MODE 11MODE 12MODE 14MODE 15MODE 16MODE 17MODE 19


Hammer Test on bridge cables

21 cos( )18

mgLChord Le LT

φ⎡ ⎤⎛ ⎞= = +⎢ ⎥⎜ ⎟⎝ ⎠⎢ ⎥⎣ ⎦

Gravity influence on the modal Variations of post-tensioned steel cables:

lengthening due to cable weight

Gravity influence on the modal Variations of post-tensioned steel cables:

lengthening due to cable weightlengthening due to cable weight

56


02

46

810

0

2

4

63

4

5

6

7

freq=12.6998 Hz

Horiz. Ham. test: impacts in 3X(12/08/04)


Hammer Test on Composite Frame

An example from the above spectral FRF measurements of the 2nd mode in X direction of the Frame (in red) is designed.

X

The FRF (Transfert Function in Fourier Space) between Acceleration at different points of the structure and Hammer load, enable to check quickly, the natural frequencies and damping of the frame and the associated mode shapes .

29

57


Fatigue testing

Example of fatigue test: 2 Megacycles on one pre-stress cable of the high speed train bridge on Po River

10.4 m

TENSACCIAI CAVO 73 TREFOLIDettaglio del carico ciclico

0

2,000

4,000

6,000

8,000

10,000

197

198

199

199

200

200

201

201

202

202

203

Tempo [s]Fo

rza

[kN

]

F.TotF.HydrosF.Moog

TENSACCIAI CAVO 73 TREFOLIDettaglio del carico ciclico

-6

-4

-2

0

2

4

6

8

197

198

198

199

199

200

200

201

201

202

202

203

Tempo [s]

Spos

tam

ento

[mm

]

D.misurD.rifer

58

Institute for the Protection and Security of the CitizenInstitute for the Protectionand Security of the CitizenGrazie della vostra attenzione !

Dedico questo corso ai Friulani colpiti dal terremoto del 6 maggio 1976. Ed in particolare a mio nono e ai parenti che hanno perso tutto in questo

tragico evento !

Terremoto del Friuli: sito di Artegna (4km del epicentro)

Vecchia costruzione in pietre Costruzione nuova con telaio in calcestruzzo + mattoni forati

30 Anni dopo…

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