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• 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

Linked to structural assessment

Sint Jacobs Church at Leuven

Maagdentoren Tower at Zichem Bell-tower the Sint-Willibrordus

Church at Meldert

Hole drilling technique3D-laserscanning

Geo-electrical survey of masonryAcoustic-Emission

Hydrostatic leveling system

‘s Hertogenmolens-watermills

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

Hole Drilling Technique – on site stress measurement

CC00CC11

CC22

CC33CC44

CC55

CC66

CC77

Based on: ASTM E837-95

Gage 1 (1)

Gage 2 (2)

Gage 3 (3)σmax

σmin

β

β

Dd

135º

(1)

(2) (3)

135º

6

Hole Drilling Technique – on site stress measurement

Sint-Jacobschurch

14º σmin = - 2.45 MPa

σmax = 0 MPa

σvert = - 2.3 MPa

10º

σmin = - 1.8 MPa

σmax = - 0.4 MPa

σvert = - 1.7 MPa

Pier 1Pier 2

Pier 2

7

Hydrostatic leveling system (HLS) Differential settlements – accuracy: 0.01 mmBased on principle of communicating vessels

d1 d2 d’1

d’2

d’12

Vessel 1 Vessel 2

Thermometer

Data-acquisition

Airwater

After vertical displacementBefore vertical displacement

Average water level

Vessel 1 Vessel 2

‘s Hertogenmolens, Aarschot (B)

8

Hydrostatic leveling system (HLS) Hydrostatic Leveling System:

-1

-0,8

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

14/07/1998 2/09/1998 22/10/1998 11/12/1998 30/01/1999

Date

Lev

el H

LS

[m

m]

0

1

2

3

4

5

6

Wat

er le

vel D

emer

[m]

HLS1 HLS2 HLS3 HLS4 HLS5 HLS6 Level Demer

23/07-18/08 19/08/1998-04/02/1999

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

1 2 3

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

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

Statements1. 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