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. 2 Preservation Process 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 Hydrostatic leveling system Hole Drilling Technique Acoustic Emission Technique Geo-electric measurements 3D-laserscanning

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

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. AB CD

5. Hole Drilling Technique – on site stress measurement C0C0C0C0 C1C1C1C1 C2C2C2C2 C3C3C3C3 C4C4C4C4 C5C5C5C5 C6C6C6C6 C7C7C7C7 Based on: ASTM E837-95 Gage 1 ( 1 ) Gage 2 ( 2 ) Gage 3 ( 3 ) σ max σ min β β D d 135º (1) (2) (3) 135º

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

7. 7 Hydrostatic leveling system (HLS) Differential settlements – accuracy: 0.01 mm Based on principle of communicating vessels d1d1 d2d2 d1d1 d2d2 d 12 Vessel 1 Vessel 2 Thermometer Data-acquisition Air water After vertical displacementBefore vertical displacement Average water level Vessel 1 Vessel 2 s Hertogenmolens, Aarschot (B)

8. 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. 123 Stress increase 3 NDT-identification of phases, within creep failure: 1.Decreasing damage rate 2.Constant slope 3.Increasing damage rate AE during creep tests – test results

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

13. 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? 14