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Monitoring for structural assessment

Monitoring for structural assessment. Koenraad Van Balen , Luc Schueremans

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Monitoring for structural assessment

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  1. Monitoring for structural assessment Koenraad Van Balen, Luc Schueremans Inauguration UNESCO Chair on Preventive Conservation, Maintenance and Monitoring of Monuments and Sites - Thematic seminar A: recording, documentation and information system for monitoring for preventive maintenance (March 25, 2009) http://www.kuleuven.be/bwk/materials

  2. Preservation Process Hydrostatic leveling system • Anamnesis: • Description and documentation of building, context (environment) • Description of building history and context • Documentation (of surveys) • Building survey, state of conservation, state of structural decay, structural investigation, using: visual inspection, NDT, semi-or least DT, … • Analysis: • Structural analysis model (idealized) • Diagnosis: • Assessment of structural integrity and its load-bearing capacity • Monitoring as part of the diagnosis • Therapy: • Plan and choices for (non-)intervention • Motivation of choices, with attention towards durability of the solution. • Execution, including control on site during execution • Control: • Maintenance plan • Monitoring Hole Drilling Technique Acoustic Emission Technique Geo-electric measurements 3D-laserscanning

  3. Linked to structural assessment Hole drilling technique 3D-laserscanning Hydrostatic leveling system Sint Jacobs Church at Leuven ‘s Hertogenmolens-watermills Geo-electrical survey of masonry Acoustic-Emission Bell-tower the Sint-Willibrordus Church at Meldert Maagdentoren Tower at Zichem

  4. 3D-laserscanning – supporting structural assessment • Calipous Limit Analysis: computer program • Analyses the stability of arches of complex geometry • Subjected to external loads or movement of abutments • Calculates: • Thrustline passing through 3 given points; • Extreme (minimum and maximum) thrustlines; • Average (minimizing sum of squares of excentricities) thrustlines. CD AB

  5. σmin (3) (2) β σmax Gage 3 (3) C0 C1 C7 β C6 C2 (1) D Gage 1 (1) C3 C5 135º d C4 135º Gage 2 (2) Hole Drilling Technique – on site stress measurement Based on: ASTM E837-95

  6. Sint-Jacobschurch Pier 2 Hole Drilling Technique – on site stress measurement

  7. Hydrostatic leveling system (HLS) Differential settlements – accuracy: 0.01 mm Based on principle of communicating vessels Vessel 1Vessel 2 Vessel 1Vessel 2 Before vertical displacement After vertical displacement d’12 d2 d1 d’1 d’2 Average water level Thermometer Air water Data-acquisition ‘s Hertogenmolens, Aarschot (B)

  8. Hydrostatic leveling system (HLS) Hydrostatic Leveling System:

  9. Acoustic Emission Measurements (AE) • “listening” to the appearance of cracks • detection of high-frequent energy waves (250-700 kHz) • possible “online-monitoring” of damage-accumulation in masonry

  10. 1 2 3 Stress increase AE during creep tests – test results • 3 NDT-identification of phases, within creep failure: • Decreasing damage rate • Constant slope • Increasing damage rate

  11. Geo-electrical measurements The measurements construct a pseudo-section, which is the graphical representation of the apparent resistivity values for a 2D-section of the masonry wall

  12. Case study: maagdentoren Zichem (B) • Dipole-dipole electrode configuration: one-sided approach Notice the historic location of the defense platforms

  13. Case study: maagdentoren Zichem (B) • outer leaf (40 cm) of heavily deteriorated ferruginous sandstone • heavily deteriorated for 50 cm behind the outer leaf (rainfall) • location of historic defense platforms: less degradation • injection with hydraulic grout is necessary

  14. Statements 1. Efforts should be done to adapt technologies that exist in others fields to be effective for monitoring and preventive conservation: YES - NO? 2. Research based on principles of preventive conservation and of monitoring should clarify the requirements requested from technologies so they can be effective for conservation and monitoring; it should be avoided that technology driven research uses heritage for its own sake. YES - NO? 3. Improvement made in electronics should contribute to developing more accessible monitoring and non-destructive techniques. YES - NO?

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