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

Roctest /SMARTEC Webinar Series June 06, 2012. Lessons learned: ten-year structural health monitoring of high-rise buildings. Branko Glišić 1 , Daniele Inaudi 2 , Joo Ming Lau 3 , and Chor Cheong Fong 3 1 Princeton University, USA (speaker) 2 SMARTEC SA, Switzerland

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

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  1. Roctest/SMARTEC Webinar Series June 06, 2012 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, Switzerland 3Housing Development Board, Singapore

  2. Introduction Monitoring criteria Monitoring method Assessment at local (column) level Assessment at global (building) level Comparison between buildings Conclusions Outline

  3. 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

  4. 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

  5. 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: 27C5C) Periodic manual measurements Yearly 48-hour sessions (include ambient temperature and relative humidity monitoring) Monitoring method

  6. 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 2nd floor Column Sensor 1st (ground) floor Foundations

  7. Sensors positions C9 UNIT F C3 C2 UNIT E C1 UNIT A C10 MULTI - STOREY VOID UNIT D C4 C7 UNIT B UNIT C C5 C6 C8 1ST STOREY FLOOR PLAN

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

  9. Photos of installation Embedding in plant Embedding on-site Passive zone Junction box SOFO sensor After pouring Measurement

  10. Completed building

  11. Results – 10 years record End of construction 48-h ‘06 48-h ‘05 Tremor 48-h ‘04 48-h ‘07 Temperature

  12. 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

  13. Average strain measured by sensor (simplified): em(t) = es(t) +ej(t) +eT(t) + esh(t) eT = thermal strain esh = total shrinkage ej = creep es = elastic strain (due to load) Estimation of total strain in columns Neglected (temperature not measured) Estimated, simplified CEB-FIP MC90 Estimated (usinges), simplified CEB-FIP MC90 Design values

  14. Measured vs. design End of constr. of 19 storeys End of constr. of 19 storeys

  15. 48-hrs 2004: strain & amb. temp.

  16. 48-hour example

  17. 48-hours example (continued)

  18. 48-hrs 2004-2007: RH & amb. temp.

  19. 24-hrs 2004 - 2007

  20. Post-tremor Analysis 48-hours 2004 Before and after tremor 48-hours 2005

  21. 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 Before settlement After settlement Shortening Shortening Elongation Settlement

  22. During Construction 2nd 4th 6th 8th 10th 12th 14th 16th 18th 5th 7th 9th 11th 13th 15th 17th 19th 0 Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 Col. 7 Col. 8 Col. 9 Col. 10 Construction of storeys Other construction works -50 -100 Development of strain for C9 unusual, column under loaded -150 ] -200 -250 -300 -350 Average strain [ -400 -450 -500 -550 -600 -650 -700 19/05/01 16/09/01 14/01/02 14/05/02 11/09/02 09/01/03 09/05/03 Age [Date+Time]

  23. Linear Correlation in long-term C5 C6 C4

  24. Linear Correlation in long-term Event

  25. Settlement in unit A v1 v2 v3 A1 A2 A3 h D L1 L2 v A1 A2 A3 h D L1 L2 C9 – over dimensioned C3 – smaller than expected C1 – bigger than expected Settlement of column C3 evaluated to ~ 0.25 to 1 mm

  26. Two Punggol EC26 Blks The same contractor, the same design, the same concrete quality Very similar results!

  27. 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

  28. 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

  29. Punggol acknowledgements Sofotec Singapore Pte Ltd

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