Use of sensors in structural engineering by pirpasha ujede
INTRODUCTION Sensors and actuators are either embedded in or attached to the system to form an integral part of it. http://www.facebook.com/pirpasha Pirpasha Ujede The structures which contain sensors, actuators can respond to counteract loads, reduces vibration, change shape and prevent their own degradation. The use of these sensors will improve the performance of structures, safety, durability, reliability, decreased life cycle costs and reduction of physical dimensions and weight.
OPTICAL FIBER SENSORS Fiber-optic sensors (also called optical fiber sensors) are fiber-based devices for sensing some quantity, typically temperature or strain, but http://www.facebook.com/pirpasha Pirpasha Ujede sometimes also displacements, vibrations, pressure, acceleration, rotation. measurement of deformations, penetration of chemicals, and so on. The general principle of such devices is that light from a laser (often a single frequency fiber laser) or from a superluminescent source is sent through an optical fiber experiences subtle changes of its parameters in the fiber and then reaches a detector arrangement which measures these changes.
ADVANTAGES They consist of electrically insulating materials. They can be safely used in explosive environments, http://www.facebook.com/pirpasha Pirpasha Ujede because there is no risk of electrical sparks. Their materials can be chemically passive, i.e., do not contaminate their surroundings and are not subject to corrosion. They have a very wide operating temperature range .
OPTICAL FIBER BRAGG GRATINGSENSORS (FBGS) Optical fiber Bragg grating sensors are strain measuring devices. http://www.facebook.com/pirpasha Pirpasha Ujede A principle operation of a fiber Bragg grating is wavelength-dependent reflector formed by introducing a periodic refractive index structure, with spacing on the order of a wavelength of light, within the core of an optical fiber. Optical Fiber Bragg grating sensors have been widely used for monitoring of civil structures like highways, bridges, buildings, dams, etc., remote sensing of oil wells, power cables, pipelines, space stations, etc.
ADVANTAGES FBGS can measure very high strain. FBGS are small sized and light weight. http://www.facebook.com/pirpasha Pirpasha Ujede FBGS are immune to electromagnetic interference. FBGS signals are not distance dependent( up to >50 km connection length is possible ). Long term stability is very high. Good corrosion resistance. Very low magnetic field interactions. Easy to install.
PIEZOELECTRIC SENSORS Piezoelectric sensors are used to detect crack in structures. http://www.facebook.com/pirpasha Pirpasha Ujede Strain changes caused by cracks in the structure are relatively small, and the resulting variations of the voltage output of the piezoelectric sensors (which are proportional to the strain changes) are difficult to be measured. For this reason, in this detection strategy two piezoelectric sensors are used. By conveniently measuring the voltage difference between the two piezoelectric strip sensors, the presence of cracks can be predicted.
HUMIDITY SENSORS Humidity sensor is base on the microwave reflection of concrete at different moisture condition. http://www.facebook.com/pirpasha Pirpasha Ujede The Humidity Sensor measures two parameters for the evaluation of the humidity content of concrete: electrical resistance and temperature. Those two measurements are performed at different depths, typically placed between the concrete surface and the reinforcement bars depth. This allows the evaluation of water content , across the concrete depth.
Pirpasha Ujedehttp://www.facebook.com/pirpasha Installation of moisture sensor
The Corrosion sensor is composed by 4 stainless steel bars that are anchored to a stainless steel support. The 4 bars are placed in the concrete at 4 different depths. The data logger measures the resistivity between pairs of bars to determine the concrete resistivity across http://www.facebook.com/pirpasha Pirpasha Ujede the depth. A low resistivity indicates higher humidity and vice versa. The concrete temperature also influences the resistivity and is therefore measured at two depths. This sensor is designed for installation in new structures or for repair work, when the concrete cover is replaced
APPLICATIONS OF SENSORS Structural Health Monitoring (SHM). Inspections for Fatigue Cracks. http://www.facebook.com/pirpasha Pirpasha Ujede Seismic Damage Identification.
STRUCTURAL HEALTH MONITORING(SHM) The process of implementing a damage detection http://www.facebook.com/pirpasha Pirpasha Ujede 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, which adversely affect the system’s performance. SHM aims to provide, in near real time, reliable information regarding the integrity of the structure.
SHM technologies detect and identify the invisible damage in the components before complete failure. The popular techniques for real-time SHM are http://www.facebook.com/pirpasha Pirpasha Ujede ultrasonic sensing (electronic) and fiber optic sensing. Ultrasonic sensing offers a wealth of information and straightforward damage detection. However, ultrasonic sensors and actuators require separate electrical wiring and perform poorly in harsh environments. Fiber optic sensors, on the other hand, offer stability in harsh environments.
These sensors provide real time monitoring of various structural changes like stress and strain. In the case of civil engineering structures, the data http://www.facebook.com/pirpasha Pirpasha Ujede 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.
THE BIGGEST ON-GOING BRIDGEMONITORING PROJECTS The Rio–Antirrio Bridge, Greece: has more than 100 http://www.facebook.com/pirpasha Pirpasha Ujede sensors monitoring the structure and the traffic in real time. Millau Viaduc, France: has one of the largest systems with fiber optics in the world which is considered state of the art. The Huey P Long Bridge, USA: has over 800 static and dynamic strain gauges designed to measure axial and bending load effects.
The Fatih Sultan Mehmet Bridge, Turkey: also known as the Second Bosphorus Bridge. It has been monitored using an innovative wireless sensor network with normal traffic condition. Tsing Ma, Ting Kau, and Kap Shui Mun bridges, Hong http://www.facebook.com/pirpasha Pirpasha Ujede Kong: approximately 900 sensors are monitoring the structure
INSPECTIONS FOR FATIGUE CRACKS The ultrasonic interrogation of components for the detection and sizing of defects has advantages over other http://www.facebook.com/pirpasha Pirpasha Ujede techniques in that surface as well as subsurface defects can be probed. The experimental configuration of our ultrasonic measurements is such that a fatigue crack is illuminated by a longitudinal wave incident perpendicular to the crack face and focussed in the plane of the crack. The longitudinal wave is partially transmitted by the closure zone and picked up by another focused receiver transducer.
By changing the angular orientation of this receiver, one can monitor the frequency, spatial, and angular dependence of the crack transmissivity. The Eddy current system can be used for inspections of http://www.facebook.com/pirpasha Pirpasha Ujede fatigue crack.
SEISMIC DAMAGE IDENTIFICATION A distributed fiber optic monitoring methodology based on optic time domain reflectometry technology is http://www.facebook.com/pirpasha Pirpasha Ujede developed for seismic damage identification of steel structures. Sensing the local deformation of the structure, the epoxy modulates the signal change within the optic fiber in response to the damage state of the structure. Damage can be identified by the optic sensors, and its maximum local deformation can be recorded by the sensing system; moreover, the damage evolution can also be identified.
CONCLUSION For the safety of a structure its strength and integrity, the sensors are used to provide real time information of the http://www.facebook.com/pirpasha Pirpasha Ujede structure. Sensors can be used to study the dynamic measurement, in the structural elements and structures buildings, bridges, dams and tanks. Because of use of these sensors we are able to get real time information of the structure and further decisions can be made with available information regarding structure strength and its life. The development and the use of these sensors are to be encouraged for the safety of the structures and life
REFERENCES www.opticsinfobase.org Dan Mateescu, Yong Han and Arun Misra “Dynamics of Structures with Piezoelectric Sensors and Actuators for http://www.facebook.com/pirpasha Pirpasha Ujede Structural Health Monitoring” Key Engineering Materials Vol. 347 (2007) pp 493-498. Encyclopedia of Laser Physics and Technology - fiber-optic sensors. Manfred Kreuzer “Strain measurement with fiber Bragg grating sensors”. Liu, Y. (2001). Advanced fiber gratings and their application. Ph.D. Thesis, Aston University.
C.R. Farrar.; S. W. Doebling and D. A. Nix (2001). "Vibration-Based Structural Damage Identification". Philosophical Transactions of the Royal Society M. Raymond. (2001). Structural Monitoring with Fiber Optic Technology. San Diego, California, USA: http://www.facebook.com/pirpasha Pirpasha Ujede Academic Press. pp. Chapter 7.