Health Monitoring of Tall RC Structures Using Instrumentation

Network

Introduction1. Civil Engineering Structures are large scale systems. They

are required to withstand different types of loads in different types environments.

2. They incur huge capital cost and have to serve a very long service life. But, they deteriorate with time as a result of aging of materials, excessive use, overloading, and inadequate maintenance.

3. Hence, durability is a paramount issue, that needs to be considered during the design process of the structural systems. Periodical monitoring of the condition (health) of these structures and suitable rehabilitation measures becomes an inevitable task.

Parameters Dictating the Durability of RC Structures • Corrosion due to chloride ion penetration,

• Corrosion due to reduction in pH (carbonation),

• Sulfate attack in foundations due to contaminated soil,

• Cracking of concrete due to various reasons (drying shrinkage, heat of hydration etc.),

• Seepage of water due to poor quality of construction,

• Cracking due to differential settlement, differential creep, and torsion.

CORROSION

Corrosion of steel in concrete structures has been a major concern of practicing engineers for the past two decades.

Corrosion loss consumes considerable portion of the budget of the country by way of either restoration measures or reconstruction.

Required Parameters to be Monitored in the Case of

Corrosion • Measurement of Chloride

Concentration with respect to the depth of concrete,

• Measurement of pH value with respect to the depth of concrete,

• Measurement of moisture level within the concrete.

Wireless Data Transmission

WSN Units

BUILDINGS

1

2

n

Sensor network

DataData StorageInternetOther Users

Local Monitoring Processor (LP)Conventional Structure Monitoring System

Structure, Sensors, Data acquisition systems, Data transfer and storage mechanism, Data Management

Wireless Structure Monitoring System

Data Acquisition

SensorsCabling

Data Acquisition

Health MonitoringPresently, some non destructive evaluation technologies such as acoustic emission, ultrasonic testing, and radar tomography are also available.

Non destructive evaluation methods are localized in scope and require knowledge of probable damage locations.

Whereas, permanent monitoring systems (sensors embedded in concrete, data acquisition, periodical monitoring and analysis of the data etc.), helps to continuously monitor the response of structures to various external loads and environmental parameters.

Global Status

Till 1970, this type of instrumentation was mostly used for nuclear industry.

Today, an attempt is being made to instrument special structures such as dams, bridges, antenna towers, hospital and high-risk facilities such as chemical or nuclear power plants with this approach.

Status in India

In India some bridges, and plants are instrumented with some facilities for monitoring parameters by using instrumentation available from foreign suppliers.

Now, this type of monitoring is required for tall buildings, important old buildings and hospitals etc.

In future, it may be mandatory for the health monitoring of the structures to meet the building codes and for protecting the human life and reducing the losses.

Future Perspectives

Traditional and wireless health monitoring system for multi-storey buildings and to take appropriate measures.

Realization of required instrumentation for health monitoring of tall buildings, with special reference to parameters like strength, moisture, length change/volume change, crack, tilt/inclination, pH of concrete, temperature and dynamic characteristics using conventional and fiber schemes.

Identification and setting the parameters such as Concrete Resistivity, CO2, pH, Temperature, RH, Chloride, Sulphate, and Corrosion Measurements to realize on line corrosion monitoring system for the RC Structures.

Future Perspectives (Contd.)

Realization of data telemetry link for multi-storied buildings,

Setting of prototype experimental building under simulated conditions for laboratory testing,

Validation and testing of instrumentation in the laboratory,

Field implementation and testing of the realized technology for structural health monitoring,

Data collection, analysis, interpretation and generation of knowledge-base.

Required Vital Parameters for Measurement

• Dynamic response (acceleration),• Strain in the structural members,• Displacement,• Inclination or tilt measurement of the structure,• Temperature variations in the structures,• Moisture movement,• Reduction in the pH,• Resistivity of concrete,• Concentration of the chloride,• Rate of corrosion,

Accelerometer

Strain meter

Crack meter

Inclination/ Tilt meter

Temperature Sensor

Displacement Sensor

Signal Conditioning

Unit

MUX

Data Acquisition System

Data Acquisition Module

Memory

Processor Module

Interface

Other Sensors

GPS Module

Direct/ Wireless Link

StructuralHealth

Junction Box

Realization of instrumentation technology for monitoring the parameters: Acceleration, Strain, Inclination, Displacement, Cracks and temperature of Tall RC Building. This work includes:

• Sensor network: Sensor interfacing, Signal Conditioning, Data Acquisition, Signal Processing, Data Storage.

• System Software and• User Interface: Data Telemetry Link

Validation and testing of instrumentation technology in lab and field. Data Computations & Analysis for damage detection, location and identification

S.No. Parameter Details

1. Acceleration( FBA or

Piezoelectric )

The measurement of dynamic response of the structures in different directions at various levels of building.

2. Strain Monitoring the vertical & horizontal bending, torsion, vertical shear force, and longitudinal compression forces developed in a structure for finding global bending moments.

3. Displacement(LVDTs/GPS)

recording displacements at rates of up to 10 samples per second with accuracy of 1cm horizontally and 2 cm vertically. GPS displacement are necessary to accurately record building drift ratios to determine that a building is overstressed.

4. Inclination/Tilt Measurement

tilt measurements will be performed with reference to the bench mark using tilt-meter periodically. Similarly, vertical settlement of the building will also be measured.

5. Temperature To calculate thermally induced strains in structures. Temperature variations in the structures will be measured to determine thermally introduced stresses at critical locations.

Physical Parameters

S.No. Parameters Details

1. Moisture Water acts as a transport agent for damaging ions such as chloride, sulfate, carbonate, and ammonium. Corrosion of steel rebars is also an important factor in assessing the useful life of concrete structures.

2. pH Value Higher pH (>12.5) of the concrete provides protective environment for the reinforcing steel against the corrosion.lower pH of the concrete endangers the rebar corrosion.

3. Open circuit potential

Embeddable reference electrodes based on Hg/HgO or MnO2 will be used for the measurement of open circuit potential .

4. Resistively of concrete

To assess the level of degradation of concrete at the cover portion in the high rise building. The measurement will be made with probes using Winner method.

5. Chloride level To measure the chloride contamination in the concrete during service life. Based on the chloride contamination the diffusion coefficient will be calculated with respect to time .

6. Corrosion rate To quantity the corrosion rate in the concrete at different levels of the structure.

Chemical parameters

Technical brief

Structure health monitoring system consists of sensors, signal conditioner, communication hardware, data acquisition and processing components to measure and assess the integrity of a structure.

The vital parameters such as acceleration, displacement, temperature, wind, load/stress, strain, tilt, inclination, pressure, deflection, moisture, cracks, high frequency vibration, audio-visual imaging, differential GPS etc. play a very important role for complete health monitoring of buildings and bridges.

Using a monitoring system to measure structural responses, a damage detection strategy will then be employed to diagnose possible short and long-term damage in a structure.

For monitoring the health of the structures, two different approaches will be taken up: traditional health monitoring system and wireless health monitoring system.

Building Monitoring

Integrated Sensors Network

On-line Structural Data Acquisition & Storage Knowledge based Integration, Data base system

Data Mining, Modeling, Analysis, and Visualization Probabilistic Analysis Statistical Pattern Recognition Service Life Prediction

Health Monitoring of Tall Structures using Instrumentation Networking

Knowledge Base & Database System for decision making Emergency Response, preventive maintenance, Retrofit / Strengthening

Continuous Monitoring & Event Monitoring

Damage Detection, Risk Analysis, Structural health Assessment

Building Blocks of Structural Health Monitoring System

Actions Required

• Identification of parameters required for health monitoring of tall buildings,• Planning of instrumentation schemes for different buildings,• Instrumentation of a few selected existing buildings,• Construction of prototype experimental building for testing under simulated

condition,• Validation of instrumentation techniques in Laboratory,• Field implementation and testing of the schemes on different typology of buildings

viz. with & without basement, stilts, age, founded on different type of strata, designed & constructed with different grade of concrete etc.

• Data collection, analysis, and interpretation,• Analytical modeling and Evaluation of buildings,• Generation of knowledge-base on durability of RC structures using Instrumentation

network,• Development of methodology for service life prediction of RC structures subjected

to chloride ion attack and carbonation effect,• Generation of knowledge-base related to response monitoring, degradation

mechanisms and life prediction of RC structures.

Actions Required (Contd.)

• Realization of instrumentation technology for monitoring the parameters : Acceleration, Strain, Inclination, Displacement, Cracks and temperature of Tall RC Buildings, which includes:– Sensor network: Sensor interfacing, Signal Conditioning, Data Acquisition,

Signal Processing, Data Storage.– System Software and User Interface– Data Telemetry Link

• Validation of instrumentation technology in lab and field implementation,• Development of sensors – Accelerometer, Inclinometer and Temperature

Sensor.• Validation of developed sensors in Lab & field implementation.• Data Analysis & interpretation of results,

Actions Required (Contd.)• Formulation of design concept for online corrosion monitoring system

(Evolve instrumentation technology to monitor pH, Chloride ion penetration, corrosion etc. in structures),

• Identification of different parameters required for Corrosion monitoring of tall buildings,

• Planning of corrosion instrumentation schemes for different buildings,• Casting of concrete specimen for laboratory and field evaluation,• Validation of sensors and hardware in laboratory,• Field implementation and testing of the scheme,• Data collection, analysis, and interpretation,• Generation of Knowledge-base.

Actions Required (Contd.)

• Sensor management:– Long-term monitoring of the identified structure for ambient

vibrations (viz. due to wind), including those due to occurrence of abnormal events, using fiber optic sensors, MEMS based and conventional accelerometers, Motes and conventional sensors, other suitable sensors.

• Data acquisition, synthesis/reduction and compression– Using remote monitoring methodologies– Comparison of the methodologies developed using the conventional

health monitoring techniques• Damage estimation and health assessment using monitored data• Residual life assessment based on health monitoring.

Thank you !!!