Structural Health Monitoring (SHM)

The process of implementing a damage detection and characterization strategy for engineering structures is referred to as Structural Health Monitoring (SHM). Here damage is defined as changes to the material and/or geometric properties of a structural system, including changes to the boundary conditions and system connectivity, which adversely affect the system’s performance. The SHM process involves the observation of a system over time using periodically sampled dynamic response measurements from an array of sensors, the extraction of damage-sensitive features from these measurements, and the statistical analysis of these features to determine the current state of system health. For long term SHM, the output of this process is periodically updated information regarding the ability of the structure to perform its intended function in light of the inevitable aging and degradation resulting from operational environments. After extreme events, such as earthquakes or blast loading, SHM is used for rapid condition screening and aims to provide, in near real time, reliable information regarding the integrity of the structure.

Health Assessment of Engineered Structures of Bridges, Buildings and other related infrastructures

Commonly known as Structural Health Assessment (SHA) or SHM, this concept is widely applied to

various forms of infrastructures, especially as countries all over the world enter into an even greater

period of construction of various infrastructures ranging from bridges to skyscrapers. Especially so when

damages to structures are concerned, it is important to note that there are stages of increasing difficulty

that require the knowledge of previous stages, namely:

1) Detecting the existence of the damage on the infrastructure

2) Locating the damage

3) Identifying the types of damage

4) Quantifying the severity of the damage

It is necessary to employ signal processing and statistical classification to convert sensor data on the

infrastructural health status into damage info for assessment.

Operational Evaluation

Operational evaluation attempts to answer four questions regarding the implementation of a damage

identification capability: i) what are the life-safety and/or economic justification for performing the SHM?

ii) How is damage defined for the system being investigated and, for multiple damage

possibilities, which cases are of the most concern?

iii) What are the conditions, both operational and environmental, under which the system to be

monitored functions?

iv) What are the limitations on acquiring data in the operational environment?

Operational evaluation begins to set the limitations on what will be monitored and how

the monitoring will be accomplished. This evaluation starts to tailor the damage

identification process to features that are unique to the system being monitored and tries

to take advantage of unique features of the damage that is to be detected.

The Fundamental Axioms of SHM

Axiom I: All materials have inherent flaws or defects;

Axiom II: The assessment of damage requires a comparison between two system states;

Axiom III: Identifying the existence and location of damage can be done in an unsupervised learning

mode, but identifying the type of damage present and the damage severity can generally only be

done in a supervised learning mode;

Axiom IVa: Sensors cannot measure damage. Feature extraction through signal processing and

statistical classification is necessary to convert sensor data into damage information;

Axiom IVb: Without intelligent feature extraction, the more sensitive a measurement is to damage, the

more sensitive it is to changing operational and environmental conditions;

Axiom V: The length- and time-scales associated with damage initiation and evolution dictate the

required properties of the SHM sensing system;

Axiom VI: There is a trade-off between the sensitivity to damage of an algorithm and its noise

rejection capability;

Axiom VII: The size of damage that can be detected from changes in system dynamics is inversely

proportional to the frequency range of excitation.

SHM Components

SHM System's elements include:

Structure

Sensors

Data acquisition systems

Data transfer and storage mechanism

Data management

Data interpretation and diagnosis:

1) System Identification

2) Structural model update

3) Structural condition assessment

4) Prediction of remaining service life

An example of this technology is embedding sensors in structures

like bridges and aircraft. These sensors provide real time monitoring of various structural

changes like stress and strain. In the case of civil engineering structures, the data

provided by the sensors is usually transmitted to a remote data acquisition centres. With

the aid of modern technology, real time control of structures (Active Structural Control)

based on the information of sensors is possible

RECENT AREA OF RESEARCH: STRUCTURAL-HEALTH-MONITORING-USING-WIRELESS-SENSOR-NETWORKS