4.0 (a) evaluation on repair work - building monitoring

8/7/2019 4.0 (a) EVALUATION ON REPAIR WORK - BUILDING MONITORING

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Monitoring System



Introduction It is essential to observe and monitor

the building conditions after repair

and rehab. It is also essential that the monitoring

procedures are specified.

An inspections shall be carried outaccording to a specific programme ±periodical chart.



Methods of monitoring

It is necessary to carefully monitorthe structural behaviour for a certainperiod of time to ascertain itsperformance.

The monitoring involve:

Carry out laboratory works

Field tests

Condition-surveys. Measurements to detect strains.

Movements, changes in reaction & deformations.



Monitoring the behaviour of a

structure Observing deflection

Visual observation

The change in the width Plumb-bobs

Opening of joints



Observing deflection By periodically taking levels.

Deformations can also be monitored

by water-levels in tubes connected totank filled with water.



Visual observation

For cracks, deflections, corrosion staining.

Particular note must be made of the cracking pattern,the crack widths and lengths and whether cracks aredue to plastic-settlement or plastic shrinkage of

concrete when the concrete was still plastic. Signs of reactive aggregates, delamination, spalling,

hollow or dead sound when tapped with hammer,honeycombing and expansion of concrete should alsobe observed.

Frequency and levels inspections have to be specified,depending on individual case circumstances.



Opening of joints

Expansion joints«.needs to beobserved.



Inspections

Corrosion monitoring

Strain measurements Use of lasers



Inspection of C.E. Structures To ensure the safety of structures

and to improve the sustainability of

large structures to avoid suddencollapses.



Main Purpose The main purpose of monitoring civil

structures is to support regular visual

examinations or inspections based onnon-destructive testing techniques.



A Monitoring Techniques A monitoring technique consist of a wireless sensornetwork using different types of sensors includingmicro-electro mechanical systems (MEMS).

Sensor networks can be used to monitor a certainregion of a structure providing data about different

physical measures. Some properties to be measured in-situ are the Eigen-

vibrations of the structure, humidity and temperatureoutside and inside the structure, unusual stress andstrain, and the detection of cracks and otherdeteriorations.

An embedded sensor system is developed to acquirethe structural condition.

A wireless network propagates the sensor data towardsa common base station where further analysis isperformed. The application of MEMS accelerators to useacoustic emission techniques is discussed.



These critical regions can further beinvestigated by RADAR and impact-echo(IE) techniques.

To characterize defects identified by amonitoring network addressing thedetection of voids and honeycombing.

Further on, a scanning IE technique is

presented to improve the reliability of suchdata and a technique to detect cracks andto obtain information about the crackdepths.



MEMS (Micro-Electro-Mechanical-

Systems) sensors MEMS are small integrated devices or

systems that combine electrical and

mechanical components that could beproduced for less than 50 ¼ each.



Fig 1. Scheme for wireless sensing of large structures usingradio frequency transmission techniques and MEMS [2, 4].

Data are sending from the base station to the supervisor using

e.g. internet



Fig 2. Size of different sensors for structural healthmonitoring used today compared to a 10 Cent ¼ coin (left)

and developed MEMS based multi-sensor system.



Fig 3. Hybrid sensor system (Smartmote) forwireless MEMS and DMS sensor data

transmission



IMPACT-ECHO TECHNIQUE Complex structures might need special

methods used by the examiner enabling fora deeper look insight the structure.

Different non-destructive testing (NDT)methods can be used as a tool in manycases and due to the demands for qualitycontrol and sustainability of structures in

civil engineering.



IMPACT-ECHO TECHNIQUE Ultrasound, radar, thermography,

electro-potential-field methods andothers are currently being used to

detect voids, cracks, corrosion. Impact-echo (IE) methods improved

the detection of voids andhoneycombing and to measure thethickness of concrete parts with goodaccuracy.



Fig 4. Close-up (left) and in-situ application(right) of the developed IE system



Application of IE techniques to

bridges The developed test system consists on the hardware

side of a transducer and a data acquisition PC card. The equipment is light, mobile and controlled by a

rugged sub-notebook or a tablet-PC. The device is

optimized for rough environments and fast and easydata acquisition. For the detection of voids and cracks, the impact

should generate a short relatively high energy butnevertheless non-destructive pulse with broadfrequency content.

The developed impactor operates on the basis of highspeed tubular solenoids meeting these requirements.It is equipped with an electronic control unitinterfacing to external devices that allows theoperator to fully control the impact generation andalso gives feedback on impact time and duration.



The IE technique has the potential to detect preciselylarge voids, honeycombs and in homogeneities as wellas the thickness of concrete structures.

In these terms it is a perfect addition to the described

monitoring system giving a more detailed insight to astructural part determined to be critical by thewireless sensors before.

The cumulative energy of the transmitted signal as acrack discriminator.

Essential is that the new system provides a morereliable impact generation.



³REAL TIME KINEMATIC GLOBAL

POSITIONING SYSTEM´ Real Time Kinematic (RTK) satellite

navigation is a technique used in land

survey and in hydrographic surveybased on the use of carrier phasemeasurements of the GPS.




POSITIONING SYSTEM´ Deformations of engineering structures such as long span

bridges, dams and tall buildings are often measured inorder to ensure that the structure is exhibiting a safedeformation behavior. It is becoming necessary to veryrapidly identify sources of unnatural variation for diagnostic

and intervention purposes. For many years, monitoring the deformation of this

engineering structure has relied on conventional geodeticmeasurements.

However, nowadays, recent advances in GPS measurementlikes a Real Time Kinematic GPS (RTK-GPS) have made it acost-effective tool for monitoring safety and performance of

engineering structures. The RTK is currently carrier phase observations processed

(corrected) in real-time resulting in position coordinateswhereby the kinematic parameters of deformation can becomputed in order to predict failure events.




POSITIONING SYSTEM´ RTK technique represents a smart

solution to the problem obtaininghigh productivity without sacrificing

very much in terms of accuracy andreliability at 2-3 cm precision.

However, the effectiveness of thistechnique is depend on radio-linkcommunication and also limited bybaseline , <10km in length.



Cambridge Monitoring System The Cambridge Monitoring System

(CMS) is a new, ultrasonic-based

monitoring system primarily forconcrete structures but with possibleapplication to structures made of other materials.



Benefits of using a CMS system Improves safety of operating concrete

structures. Helps make better use of repair budgets by

directing inspection or repair to where mostchange is happening. Extends working life of older structures -

particularly beyond the normal working life. Low annual running costs - automated

system does not need a full-time operator. Provides audit trail of any structural change

in the event of litigation relating tointegrity.



How CMS works Network of intelligent, CMS sensors is attached to the

structure to be monitored and connected by cable orradio back to an Archive PC.

Each sensor injects a known pattern of waves into the

part of the structure to which it is attached and eachsensor collects echo-waves back from the interior of the structure.

CMS is not an acoustic monitoring system, which is apassive monitoring system and which is potentiallyvery sensitive to operational noise. Signals are sentfrom each sensor to the Archive PC according to aschedule of tests controlled from the Archive.



Conclusi

on

Instrumentation/monitoring

Crack movement

Deformations Stresses

Timing/costs



References1. Christian U. Grosse & Markus Krüger

(2006),Inspection and Monitoring of Structuresin Civil Engineering, Vol.11, No.1, NDT.net.

2. Grosse, C. U., H. W. Reinhardt, M. Krüger and R.

Beutel.2005. "Application of Impact-echo techniquesfor crack detection and crack parameter estimationin concrete", extended abstract, InternationalConference on Fracture ICF-11, Turin 20-25 March2005, (on CD-ROM).

3. Dr. Edward C.Y. Yiu, Assistant Professor atDepartment of Real Estate & Construction, TheUniversity of Hong Kong

4.0 (a) evaluation on repair work - building monitoring

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