Encardio-Rite: A Guide on Structural Health Monitoring (SHM)

August 22, 2019

Credits: Encardio-Rite | Geotechnical Instrumentation Company

With technological advancements in the field of civil engineering and geotechnical engineering, the magnificent structures like Burj Khalifa and Gotthard Base Tunnel have been made possible.

Humans have built large structures like dams, tunnels, skyscrapers, power plants etc. to make their life easier.

But even a minor failure in these structures can cause loss of property as well as human life.Hence, regular structural health monitoring is a must.

Let’s discuss more on structural health monitoring, geotechnical instrumentation, and how it makes the world a safer place to live.

What is meant by Structural Health Monitoring?

Structural health monitoring is vital to avoid sudden failures and accidents. Before proceeding with any construction activity, it’s necessary to carry out the monitoring of the construction site as well as the nearby assets.

Geotechnical instrumentation and monitoring supply quantitative data on the structure’s performance to aid in evaluating its safety and detecting problems at an early stage.

Structures can fail due to several reasons like design error, geological instability, poor maintenance, deterioration of construction material, etc.

Structural health monitoring is a process to keep an eye on all the structures and generate early warnings to avoid mishaps.

Encardio-rite is geotechnical instrumentation and monitoring company that provides various monitoring services along with state-of-the-art geotechnical instruments.

Why is Geotechnical Monitoring important?

Geotechnical monitoring is an important matter of economic benefit as well as public safety.Sudden structural failures can threaten life and property.

The main purpose of structural health monitoring is to supply quantitative performance data to the concerned authority.

Geotechnical monitoring can prove beneficial at the following stages of construction:

Site investigation

Site investigation is crucial before carrying out any construction activity.

It is important to check if the land is strong enough to bear the structure. Apart from this, it is essential to check for the safety of other assets in the vicinity of the construction land.

Several geotechnical Instruments are used to characterize and determine initial site conditions.

The most common parameters of interest in a site investigation are pore pressure, the permeability of the soil, slope stability etc.

Design verification

It is quite important to verify the design of the structure. Improper designing may lead to its failure.

Geotechnical instruments are used to verify design assumptions.Instrumentation data from the initial stage of a project may show the need or provide the opportunity to modify the design in later stages.

For example, data obtained from reinforcement bar strain meters installed by Encardio-rite at Teesta Barrage in the left embankment led the project authorities to revise their estimates of the requirement of steel in the right embankment.

Construction control

Structural monitoring is necessary to help the engineer in determining how fast construction can proceed without adverse effects on the foundation soil and construction materials used.

The instruments are installed to monitor the effects of construction.

For example, the temperature rise in concrete due to heat of hydration was monitored at Sardar Sarovar Dam on the Narmada River with Encardio-rite’s temperature meters to determine the pouring temperature of mass concrete.

By mixing ice flakes, the temperature of the concrete to be poured was brought down to around 15°C.

This resulted in the temperature of the setting concrete not exceeding the critical 29°C, as specified and required by the Central Water and Power Research Station (CWPRS), Pune.

Safety

Instruments can provide early warning of impending failure. Safety monitoring requires quick retrieval, processing, and presentation of instrument data so that analyses and decisions can be made promptly.

An effective action plan for implementing corrective measures can then be prepared.

| Read More: Geotechnical Instrumentation & Monitoring: Services &Types |

Advantages of Structural Health Monitoring

Structural health monitoring (SHM) is critical because:

1. It can provide early warning to the concerned authorities so that they can take actions well before any casualties.
2. It keeps a regular check on the health of structures so that sudden failures can be avoided.
3. It safeguards human life as well as the loss of property.
4. It also protects the surrounding structures in the vicinity.
5. It increases the life span of the structures.
6. It reduces the long-term and short-term costs related to structural maintenance.
7. It monitors the performance for safety during the life of the structure.
8. It evaluates the effect of the operation of the structure on parameters like stress, strain, water, pressure, inclination, deflection and water seepage.
9. It compares the observed data with design assumptions.
10. It helps with the data to plan and schedule predictive and preventive maintenance programs for the structure.
11. It provides data to determine the effects of natural calamities such as earthquake, flooding etc. on the structure.
12. Compilation of long-term and reliable data on the various elements of the plant especially foundations, anchoring systems and containment structures.

How does Structural Health Monitoring work?

Structural health monitoring requires several geotechnical instruments installation.The instruments like strain gauges, piezometers, tilt meters, temperature sensors, pressure cells, load cells etc. measure the crucial parameters affecting the structures.

These instruments are installed on dams, tunnels, nuclear power plants, buildings, monuments to measure the important parameters.

The measured data is logged in real-time through data loggers and displayed via a PC/laptop/mobile device at any remote location.

The data loggers are capable of generating early warnings such that the concerned person can take actions accordingly.

Structural Health Monitoring of Bridges

There are numerous rail and road bridges built across the globe. They are an essential component of transportation networks and, hence, structural health monitoring of bridges is crucial.

Any damage or collapse of bridges due to their deteriorating performance disrupts transportation systems and may result in the loss of life as well as property.

The railway bridges are well documented and have a laid down system for checking and maintenance.

The Ministry of Road Transport & Highways in India has established an Indian Bridge Management System (IBMS) to carry out condition surveys and instrumentation of all bridges on National Highways in India.

Till date, an inventory of more than 170,000 bridges and culverts has been compiled.

Bridges must function safely at all times. A large number of bridges are quite old and not designed for the heavier and faster-moving vehicular loads that they are currently subjected to.

Online cloud-based web data monitoring service

Encardio-rite offers public cloud-based online web data monitoring services for the safety of existing rail and road bridges.

The heart of the online structural monitoring instrumentation system is a web data monitoring service (WDMS) offered by Encardio-rite. The service forms an important part of the Bridge Management System.

It is a web-based data-management and presentation tool for retrieving data from the sensors through Encardio-rite range of automatic data loggers.

WDMS consists of Drishti, data management software that acts as a data collection agent, a database server and a web server hosted on a high-reliability server computer.

The host computer periodically collects data from the remote data logger over cell phone networks.

Users interact with the software using their web-browser when connected to the Internet. The only requirement is that the data logger site is covered by a cell phone service provider who can provide reliable GSM/GPRS enabled cellular data connection locally.

Multiple authorized users at different locations assigned with an individual password are allowed to view any data or report from the structure simultaneously.

Graphs & reports can be viewed using popular web browsers like Microsoft internet explorer or Mozilla Firefox amongst others.

Details like sensor identification tag, last recorded sensor reading and values of programmed alert levels can be viewed on the first page of the site that shows the location of installation.

If anyone of the alarm level exceeds, the sensor location turns to a red dot.

Clicking the pop-up table brings up an associated data window where the sensor data can be seen either as a table or as a graph.

Site administrators can set alarm limits which are generally considered as “alert level” and “action level”.

WDMS can also be programmed to send SMS alert messages or e-mail to selected users as soon as any sensor data crosses its predefined alarm levels, either while going above or going below the alarm level.

Bridge Monitoring Instrumentation Scheme

There are two types of instrumentation schemes to monitor the health of the bridges.

Figure 1: Online web based monitoring of surface parameters like tilt, crack, load, strain, vibrations and subsurface parameters like lateral movement, settlement and piezometric pressure.

Figure 2: Online web based monitoring of lateral movement and settlement using robotic total stations and prism targets

The picture on the left is a typical installation of a robotic total station installed to automatically gather data from prism targets installed on the structure of a bridge.

The picture in the middle is that of a mini prism target.

The figure on the right shows points at which prism targets may be installed on a typical bridge. More than one robotic total station may be required for proper monitoring of a structure.

| Read More: A Guide on Geotechnical Instruments: Types, & Application |

Screenshots of some sample long term monitoring data

The figure above shows structural crack monitoring over a period of one year using Encardio-rite Model EDJ-40V crack meter. Crack opening is in blue and variation in temperature is in red. The initial opening of the crack gauge was set at 5.12 mm.

The above image shows the structural tilt monitoring of the bridge from September 12, 2015 to December 8, 2016 using Encardio-rite Model EAN-92M biaxial tilt meter.

Tilt variation in the two directions is shown by the blue and black lines..[Continue Reading]