lessons learned: ten-year structural health monitoring of high-rise buildings

©SHM Lab, SMARTEC, HDB

Lessons learned: ten-year structural health monitoring of high-rise

buildings

Branko Glišić1, Daniele Inaudi2, Joo Ming Lau3, and Chor Cheong Fong3

1Princeton University, USA (speaker)2SMARTEC SA, Switzerland3Housing Development Board, Singapore

Roctest/SMARTEC Webinar SeriesJune 06, 2012

©SHM Lab, SMARTEC, HDB 2/29Ten-year SHM of high-rise buildings

• Introduction

• Monitoring criteria

• Monitoring method

• Assessment at local (column) level

• Assessment at global (building) level

• Comparison between buildings

• Conclusions

Outline


Punggol project – introduction • Collaborative study between HDB – Singapore’s

Public Housing Authority & Smartec, Switzerland• Purpose of study

– As a part of quality assurance, preventive maintenance– Understanding of structural behavior

• Long-term lifespan structural monitoring • Fiber optic sensing monitoring system used

based on low coherence interferometry• ~400 buildings equipped with sensors• 10+ years long-term monitoring: monitoring

during construction, 48-hours continuous sessions, post-tremor evaluation


• Critical structural members to be monitored

• Local (column) and global (building) structural monitoring required

• Long-term lifespan monitoring incl. construction

• Structural (not material) monitoring required

• Costs for monitoring to be affordable

Monitoring criteria


• Critical structural members selected based on numerical modeling• Structural monitoring long-gage sensors• Long-term monitoring incl. construction embeddable fiber optic

sensors• Affordable costs

– Only 10 columns monitored– No temperature monitoring (yearly variation in Singapore:

27C5C)– Periodic manual measurements – Yearly 48-hour sessions (include ambient temperature and relative

humidity monitoring)

Monitoring method


• No bending in columns single sensor per column

• Data analyzed at both local (column) level and global (building) level

• Several neighboring buildings built by same contractor, with same design and concrete quality, and instrumented with similar monitoring system possible comparison between buildings

Monitoring method, continued

1st (ground) floor

2nd floor

Foundations

Co

lum

n

Sen

sor


Sensors positions

C10

C3

C4

C5C6

C7

C8

C2

C1

C9

1ST STOREY FLOOR PLAN

MULTI - STOREY VOID

UNIT A

UNIT B

UN

IT C

UNIT D

UNIT EUNIT F


Construction stage

• Six blocks founded on piles• 19 storeys tall, 6 units per storey• Columns are cast in-situ


Embedding on-site

SOFO sensor

Passive zone

Junction box

Embedding in plant

After pouring Measurement

Photos of installation


Completed building


Results – 10 years record

48-h

‘04

Trem

or

End of construction

48-h

‘05

48-h

‘06

48-h ‘07 Temperature


• Sensors measure axial deformation in columns• Determine measured strain in columns• Evaluate whether strains is acceptable by

– Comparison between measured strain and estimated theoretical (design) values

– Comparison between measured strain and ultimate strain

• Use 48-hours campaigns in order to:– Learn the building behaviour caused by daily temperature

changes and inhabitant fluctuations– Record the health state of the building as a reference for

comparison with the future monitoring results

Assessment at local level


Average strain measured by sensor (simplified):

m(t) = s(t) +(t) +T(t) + sh(t)

T = thermal strain

sh = total shrinkage

= creep

s = elastic strain (due to load)

Neglected (temperature not measured)

Estimated, simplified CEB-FIP MC90

Estimated (using s), simplified CEB-FIP

MC90 Design values

Estimation of total strain in columns


Measured vs. designStrain components, column C9

-700

-600

-500

-400

-300

-200

-100

0

24.05.01 24.05.02 24.05.03 23.05.04 23.05.05

Time

Av

era

ge

str

ain

[m ]

Measured (total)

Shrinkage (CEB-FIP)

Creep (CEB-FIP)

Load (design)

Total (design)

Strain components, column C3

-700

-600

-500

-400

-300

-200

-100

0

24.05.01 24.05.02 24.05.03 23.05.04 23.05.05

Time

Ave

rag

e st

rain

[m ]

Measured (total)

Shrinkage (CEB-FIP)

Creep (CEB-FIP)

Load (design)

Total (design)

End of constr. of 19 storeys End of constr. of 19 storeys


48 hours, total av. strain, C6 (1683)

-594

-592

-590

-588

-586

-584

-582

-580

-578

-576

-574

-572

01.07.0412:00

01.07.0420:00

02.07.0404:00

02.07.0412:00

02.07.0420:00

03.07.0404:00

03.07.0412:00

Time [date & hour]

Ave

rag

e st

rain

[m ]

20

21

22

23

24

25

26

27

28

29

30

31

Am

b. t

emp

erat

ure

[°C

]

C6 (1683)

Amb. temp.

48-hrs 2004: strain & amb. temp.



-652-650-648-646-644-642-640-638-636-634-632-630-628-626-624-622-620-618-616-614-612-610-608-606-604-602

10:0

0

12:0

0

14:0

0

16:0

0

18:0

0

20:0

0

22:0

0

00:0

0

02:0

0

04:0

0

06:0

0

08:0

0

10:0

0

12:0

0

14:0

0

16:0

0

18:0

0

20:0

0

22:0

0

00:0

0

02:0

0

04:0

0

06:0

0

08:0

0

10:0

0

12:0

0

14:0

0

Time [hour]

Ave

rag

e st

rain

[m ] C4 (1669) 2004 C4 (1669) 2005

C4 (1669) 2006 C4 (1669) 2007

48-hour example



-602-600-598-596-594-592-590-588-586-584-582-580-578-576-574-572-570-568

10:0

0

12:0

0

14:0

0

16:0

0

18:0

0

20:0

0

22:0

0

00:0

0

02:0

0

04:0

0

06:0

0

08:0

0

10:0

0

12:0

0

14:0

0

16:0

0

18:0

0

20:0

0

22:0

0

00:0

0

02:0

0

04:0

0

06:0

0

08:0

0

10:0

0

12:0

0

14:0

0

Time [date & hour]

Ave

rag

e st

rain

[m ]

C6 (1683) 2004 C6 (1683) 2005

C6 (1683) 2006 C6 (1683) 2007

48-hours example (continued)


48 hours averaged ambient temperature '04,'05, '06 and '07

24

25

26

27

28

29

30

31

Ave

rag

ed A

mb

. T

emp

erat

ure

[°C

]Averaged 2004 Averaged 2005

Averaged 2006 Averaged 2007

48 hours averaged relative humidity '04, '05, '06 and '07

60%

65%

70%

75%

80%

85%

Rel

ativ

e H

um

idit

y [%

]



48-hrs 2004-2007: RH & amb. temp.


48 hours averaged strain 2004, 2005, 2006 and 2007

-800

-780-760

-740

-720-700

-680

-660-640

-620-600

-580

-560-540

-520

-500-480

-460

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10

Ave

rag

ed s

trai

n [

m ]

Averaged 2004

Averaged 2005

Averaged 2006

Averaged 2007

24-hrs 2004 - 2007


Punggol EC26, post-tremor evaluation

-800

-750

-700

-650

-600

-550

-500

-450

12.06.04 11.09.04 11.12.04 12.03.05 12.06.05

Time [date & hour]

Avera

ge s

train

[m ]

C1 (1675)

C2 (1668)

C3 (1676)

C4 (1669)

C5 (1663)

C6 (1683)

C7 (1670)

C8 (1682)

C9 (1662)

C10 (1677)

48-hours 2004 Before and after tremor

48-hours 2005

Post-tremor Analysis


• Comparison of strain development of columns per units A, B, C and E

• Comparison of differential deformation of columns• Statistical analysis

Assessment at Global Level

Settlement

After settlementBefore settlement

Sh

ort

enin

g

Elo

ng

atio

n

Sh

ort

enin

g


-700-650-600-550-500-450-400-350-300-250-200-150-100-50

0

19/05/01 16/09/01 14/01/02 14/05/02 11/09/02 09/01/03 09/05/03

Age [Date+Time]

Ave

rag

e st

rain

[]

Col. 1

Col. 2

Col. 3

Col. 4

Col. 5

Col. 6

Col. 7

Col. 8

Col. 9

Col. 10

19th 17th 15th 13th 11th 9th 7th 5th 18th 16th 14th 12th 10th 8th 6th 4th 2nd

Construction of storeys Other construction works

Development of strain for C9 unusual, column under loaded

During Construction


Unit B - correlation with C4

-800

-700

-600

-500

-400

-300

-200

-100

0

-700 -600 -500 -400 -300 -200 -100 0

Measurement of column C2 [m]

Mea

sure

men

ts o

f co

lum

ns

C1

and

C3

[m ]

C5 (1663)

C6 (1683)

C4

C5

C6

Linear Correlation in long-term


Linear Correlation in long-termUnit A - correlation with C2

-800

-700

-600

-500

-400

-300

-200

-100

0

-700 -600 -500 -400 -300 -200 -100 0

Measurement of column C2 [m ]

Mea

sure

men

ts o

f co

lum

ns

C1

and

C3

[m ]

C3 (1676)

C1 (1675)

Event


Settlement in unit A

h

L1 L2

A1 A2 A3

v1 v2 v3

h

L1 L2

A1 A2 A3

v

C3 – smaller than expected C1 – bigger than expected

Settlement of column C3 evaluated to ~ 0.25 to 1 mm

C9 – over dimensioned


Punggol EC26 Blk166B - June 01 - March 05

-800

-700

-600

-500

-400

-300

-200

-100

0

09/06/20010:00

27/01/20020:00

16/09/20020:00

06/05/20030:00

24/12/20030:00

12/08/20040:00

01/04/20050:00

Time

Ave

rag

e st

rain

[]

S1671 S1681

S1680 S1678

S1679 S1673

S1674 S1666

S1667 S1664

-800

-700

-600

-500

-400

-300

-200

-100

0

09/06/20010:00

27/01/20020:00

16/09/20020:00

06/05/20030:00

24/12/20030:00

12/08/20040:00

01/04/20050:00

Two Punggol EC26 BlksPunggol EC26, May 2001-April 2005

-800

-700

-600

-500

-400

-300

-200

-100

0

24/05/2001 0:00

22/11/2001 12:00

24/05/2002 0:00

22/11/2002 12:00

24/05/2003 0:00

22/11/2003 12:00

23/05/2004 0:00

21/11/2004 12:00

23/05/2005 0:00

Time [date & hour]

Ave

rag

e st

rain

[]

C1 (1675) C2 (1668)

C3 (1676) C4 (1669)

C5 (1663) C6 (1683)

C7 (1670) C8 (1682)

C9 (1662) C10 (1677)

The same contractor, the same design, the same concrete quality

Very similar results!


Conclusions Detected under-loading of column C9 helps designer to

understand real structural behavior and improve modeling Differential settlements detected, localized, and

characterized – small magnitude, doesn't influence the performance of building; settlement is however not stabilized yet and monitoring should continue

The 48-hours sessions confirmed sound performance of the building in long-term and made possible post-tremor analysis (no need to evacuate the building due to event)

The creep and shrinkage stabilizes slowly (creep developed ~97% and shrinkage ~84% approximately) and dominant influence is ambient temperature

Quality control performed by comparison of behavior of different building


Conclusions, continued Enlarged knowledge concerning the real column behavior

during construction (rheological effects) In spite of limitations (temperature not monitored, no

continuous readings) results leads to important insights on actual behavior

Pioneer monitoring project for Singapore high-rise buildings: 10-years long-term monitoring successfully performed and important stages in structure life registered

Monitoring method developed and successfully applied, monitoring system was properly selected and fully responded to design criteria

10 out of 10 long-gauge fiber optic sensors properly function after 10+ years


Punggol acknowledgements

Sofotec Singapore Pte Ltd

lessons learned: ten-year structural health monitoring of high-rise buildings

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