Structural Monitoring and Status-Dependent Maintenance and

Laboratory validation Laboratory validation of intelligent structure technologiesof intelligent structure technologies

D. ZontaUniversity of Trento

MEMSCON WorkshopMEMSCON WorkshopStructural Monitoring and StatusStructural Monitoring and Status--DependentDependent

Maintenance and Repair of Constructed FacilitiesMaintenance and Repair of Constructed FacilitiesBucharest, 7 October 2010Bucharest, 7 October 2010

D. Zonta - Laboratory validation of intelligent structure technologies

MEMSCON EU project

MISSIONDevelopment of a reliable and cost-efficient monitoring system to be integrated in new Reinforced Concrete (RC) buildings for their protection against seismic events and settlement.

OBJECTIVES(i) development of a wireless sensing network, including creation of new dedicated instruments for strain and acceleration measurement.

(ii) development of a Decision Support System (DSS) for remote data processing, structure condition assessment and for maintenance planning.

VALIDATIONThe products are to be validated both in the laboratory and in on-site applications.


WSN schemeThe system includes a wireless network within the building and a base station linking the building to a remote centre for data interpretation.Strain measurements are collected at the lowest level of the building, to estimate the vertical column loads and any variation due to settlement;Horizontal acceleration is measured by dedicated nodes at each level during an earthquake, allowing analysis of the seismic response of the whole structure.


to be donedone

Timeline

24 300 366 12 18 27 333 9 15 21

oct dec feb apr jun ago oct dec feb apr jun ago oct dec feb apr jun ago

2009 2010 20112008

now

monthpr

oduc

ed

valid

ated

prod

uced

valid

ated

inst

alle

d

Phase I prototypes: assembled from components available on the market, with the necessary design, packaging and programming. They do not fulfil the target requirements, but they let us investigate the relevant features.Phase II prototypes: definitive tools.

Phase I prototypes

Phase II prototypes


Phase I accelerometer

Tri-axial accelerometers

Sampling rate: 100Hz

Resolution: 18mg (=0.18m/s2)

Range: from -2g to +2g(from -20m/s2 to +20m/s2)

Sampling period: up to 30 seconds

packaged in 11x8x4cm plastic boxes;

19cm high antenna

weight of a sensor is 150g

x

y

z


Phase II accelerometer


Calibration testsThe shaking table has been driven using harmonic excitations at different frequencies:

1Hz, 2Hz, 4Hz, 8Hz and 16Hz

The tests were repeated at different amplitudes:

about ±1m/s2 (±0.1g) and about ±4m/s2 (±0.4g)


Calibration testFrequency: 4 Hz Amplitude: ± 1.1 m/s2 Axis: Y

5 10 15 20

-1

0

1

Acc

[m/s

2 ]

WL1 - Scale Factor 1.005

5 10 15 20

-1

0

1

Acc

[m/s

2 ]


5 10 15 20

-1

0

1

Time [s]

Acc

[m/s

2 ]


WL3B12-2

WL2B31

WL1B12-1


0 2 4 6 8 10 12 14 16 18 20-5

0

5

Erro

r [%

]

FREQUENCY ERRORS - X DIRECTION - LOW AMPLITUDE WL1 Freq ErrorsWL2 Freq ErrorsWL3 Freq Errors

0 2 4 6 8 10 12 14 16 18 20-5

0

5

Erro

r [%

]

FREQUENCY ERRORS - Y DIRECTION - LOW AMPLITUDE WL1 Freq ErrorsWL2 Freq ErrorsWL3 Freq Errors

0 2 4 6 8 10 12 14 16 18 20-5

0

5

Freq Shaker [Hz]

Erro

r [%

]

FREQUENCY ERRORS - Z DIRECTION - LOW AMPLITUDE WL1 Freq ErrorsWL2 Freq ErrorsWL3 Freq Errors

Calibration outcomesaxis: X

axis: Y

axis: Z


Earthquake simulationsAdditional tests have been carried out to simulate the effect of a seismic motion.

2-storey reduced-scale steel frame mounted on the table,

3 different vibration time histories

Mass per storey:about 8Kg

Natural Frequency:First mode: 2.1HzSecond mode: 5.2Hz

Damping:About 1‰

referencesensors

WL sensors


0 5 10 15 20 25 30 35-10

0

10

Acc

[m/s

2 ]

Ground - Delay 0 sec - Scale Factor 1.005WL1PCB-B31

0 5 10 15 20 25 30 35-10

0

10

Acc

[m/s

2 ]

First Floor - Delay 0.29 sec - Scale Factor 0.97561WL2B12-1

0 5 10 15 20 25 30 35-10

0

10

time [s]

Acc

[m/s

2 ]

Second Floor - Delay -0.08 sec - Scale Factor 0.99206WL3B12-2

EQ time history


Accelerometers: achievements

- after calibration, the prototypes respond consistently with references sensors

- precision is in the order of the resolution (0.2m/s2)

- the initialization procedure is very easy and the operation reliable

- the wake-up procedure, which permits the devices to transmit only if a large vibration has been recorded (>0.5m/s2), is efficient.


Phase I strain gaugeMono-axial strain gauge

Sampling rate: 3Hz

Resolution: 20

Range: from -40m to +40m

2.7

5.9

3.0 10.9

[mm]

metal foils strain gauge

HBM model LY41-3/700

Carrier in polyimide,

45m thickness

Nominal resistence: 700.

Nominal maximum elongation: 5%.


Phase II strain sensor

Battery life >= 2 yearspower consumption < 5mA

Measurement range +/-30’000 µεAccuracy 10 µεBias with temperature 0.1 µε/°C






Phase II strain sensor: packaging

Rebar

Rebar Clip

PDMS (or PU)

Readout Asic

Strain sensor

Ribbon wire

Form

To external radio

Rebar

Rebar Clip

PDMS (or PU)

Readout Asic

Strain sensor

Ribbon wire

Form

To external radio


3.1.3a: bare bars

500

WLwired

WLwired

1002 bars have been produced

tensile test

AIM:

to check the accuracy of the system avoiding all the uncertainties of concrete behaviour


Tensile tests on bare rebars

0 1000 2000 3000 40000

50

100

150

200

Strain []

Load

[kN

]

WL10WL12SG1SG2

0 500 1000 1500 2000 25000

1000

2000

3000

4000

Time [sec]

Stra

in [ ]

WL10WL12SG1SG2


3.1.3b: Bars in concrete

500WL

860

130

WL

wired

WL

wired

rebar

concrete

instrumentedsection

tensile test


AIM:

to investigate the performance of the gauges inside concrete, before and after cracking

wiredcrack


3.1.3b: Bars in concrete


Tensile test

WL SGs

wired SGs

Force


3.1.2: compressive test specimen

330

130

rebar

concrete

WLwired

stirrup


AIM:

analyze the behavior of the gauges embedded into concrete in compression

compressive test


3.1.2: compressive test specimen


Compressive test outcomes

WL 1

wired 1

WL 2

wired 2


Tests on full scale columns

1.65 m

2.35 m

Column section

Beam section

30 cm

30 cm

70 cm

30 cm3.50 m


Target prototype building

T [sec]

Sa [m/s2]

0,4

7,7

1,3

Building description:

column grid: 6x6 m,

3 floors,

q = 5,85 (frame building in high ductility class)

Seismic action:

ag = 0,25 g

T1 = 0,39 sec

M N V

h

h/2

NV

Cantilever specimen

plastic hinge

N = 786 kN

V = 105 kN

M = 150 kNmM N V


Tests on full scale columns

strain gauge position

instrumented cross section


Specimen design


Instrumented reinforcement


Steel cage


Detail of the instrumented node


Specimen ready to test


Laboratory set up

2 orthogonalactuators

anchorages


Laboratory set up


Test outcomesTest on Column 3,

vertical load: 800KN,horizontal displacement: up to ±80mm


Test outcomes

0 500 1000 1500 2000 2500 3000 3500 4000-4-2024

stra

in [m

]

0 500 1000 1500 2000 2500 3000 3500 4000-4-2024

stra

in [m

]

0 500 1000 1500 2000 2500 3000 3500 4000-4-2024

stra

in [m

]

0 500 1000 1500 2000 2500 3000 3500 4000-4-2024

stra

in [m

]

time [sec]

s1

s2

s3

s4


Strain sensors: achievements

- the strain recorded by the prototypes is consistent with that of the wired ones with a precision (30), which is in the order of the resolution of the sensors (20);

- the initialization procedure is very easy and the operation is reliable (no communication problem observed);

- observed deboning at 3000 of commercial strain gauges that will be overcome by developing Phase II sensors


Conclusions

- MEMSCON project aims to develop a new generation of wireless sensors dedicated to civil engineering applications

- to date we tested a first batch of sensors assembled from components available on the market

- validation tests highlighted limitations of commercial sensors: power consumption and accuracy for accelerometers, packaging system for strain gauges

- these limitations will be overcome by Phase II sensors


Thank you for your attention!

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Structural Monitoring and Status-Dependent Maintenance and