Structural health monitoring

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Structural health monitoring (SHM) is an upcoming technology in civil, mechanical, and aerospace engineering. In the last ten to fifteen years, SHM technologies have emerged creating an exciting new field within various branches of engineering. These technologies are currently becoming increasingly common. SHM is a new approach to collect data about critical structural elements using sensors to provide indicators when some anomalies are detected in a structure. This approach will continuously update the data in a structure on current conditions of a structure including the detection of changes in chemical and electrical properties of materials related to deterioration, such as corrosion and chloride attack, steel corrosion and fatigue, alkali-silica reaction, and PH, humidity and changes in the service environment or exposure. SHM can also continuously monitor structure physical properties, such as loadings, stresses, strains, accelerations, cracks, etc. [1] SHM refers to the broad concept of assessing the ongoing, in-service performance of structures using a variety of measurement techniques.

Contents

[edit] SHM Components

SHM System's elements include:

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

[edit] Examples

Wind and Structural Health Monitoring System for Bridges in Hong Kong: The Wind and Structural Health Monitoring System (WASHMS) is a sophisticated bridge monitoring system, costing US$1.3 million, used by the Hong Kong Highways Department to ensure road user comfort and safety of the Tsing Ma, Ting Kau, and Kap Shui Mun bridges that run between Hong Kong and the Hong Kong Airport.

In order to oversee the integrity, durability and reliability of the bridges, WASHMS has four different levels of operation: sensory systems, data acquisition systems, local centralised computer systems and global central computer system.

The sensory system consists of approximately 900 sensors and their relevant interfacing units. With more than 350 sensors on the Tsing Ma bridge, 350 on Ting Kau and 200 on Kap Shui Mun, the structural behaviour of the bridges is measured 24 hours a day, seven days a week.

The sensors include accelerometers, strain gauges, displacement transducers, level sensing stations, anemometers, temperature sensors and dynamic weight-in-motion sensors. They measure everything from tarmac temperature and strains in structural members to wind speed and the deflection and rotation of the kilometres of cables and any movement of the bridge decks and towers.

These sensors are the early warning system for the bridges, providing the essential information that help the Highways Department to accurately monitor the general health conditions of the bridges.

The structures have been built to withstand up to a one-minute mean wind speed of 95 metres per second. In 1997, when Hong Kong had a direct hit from Typhoon Victor, wind speeds of 110 to 120 kilometres per hour were recorded. However, the highest wind speed on record occurred during Typhoon Wanda in 1962 when a 3 second gust wind speed was recorded at 78.8 metres per second, 284 kilometres per hour.

The information from these hundreds of different sensors is transmitted to the data acquisition outstation units. There are three data acquisition outstation units on Tsing Ma bridge, three on Ting Kau and two on the Kap Shui Mun.

The computing powerhouse for these systems is in the administrative building used by the Highways Department in Tsing Yi. The local central computer system provides data collection control, post-processing, transmission and storage. The global system is used for data acquisition and analysis, assessing the physical conditions and structural functions of the bridges and for integration and manipulation of the data acquisition, analysis and assessing processes.

[edit] Structural Health Monitoring for bridges

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Please improve this article if you can (February 2008).

Health monitoring of large bridges shall be performed by simultaneous measurement of loads on the bridge and effects of these loads. It typically includes monitoring of:

  • Wind and weather
  • Traffic
  • Prestressing and stay cables
  • Deck
  • Pylons
  • Ground

Provided with this knowledge, the engineer can:

  • Estimate the loads and their effects
  • Estimate the state of fatigue
  • Forecast the probable evolution of the bridge

[edit] References

  1. ^ Darbani, B.M., and Hammad, A.(2007) "Critical Review of New Directions in Bridge Management Systems", AASCE conference of Computing in Civil Engineering 2007, Pittsburgh, PA.

[edit] See also

[edit] External links

[edit] Journals of Structural Health Monitoring

Journal of Structural Health Monitoring(sagepub)

Structural Control and Health Monitoring (wiley)

Smart Materials and Structures (IOP)

Smart Materials Bulletin (science direct)

Intelligent Material Systems & Structures(ASME)

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