20-04-2012, 03:01 PM
INTELLIGENT SKYSCRAPER MONITORING SYSTEM BASED ON GPS AND OPTICAL FIBRE SENSORS
[attachment=20453]
INTRODUCTION:
The collapse of the World Trade Center (WTC) twin tower has caught many people by surprise and has reminded us of the importance of structural integrity monitoring for improving disaster preparedness and response. “Nobody thought it (WTC) would collapse!” The sentence has been repeated many, many times in the media on the first anniversary of 11 September 2001. The events following the 11 September 2001 attacks in New York City were among the worst building disasters in history and resulted in the largest loss of life from any single building collapse in the United States. Of the 58,000 people estimated to be at the WTC Complex, over 3,000 lost their lives that day, including 343 emergency responders. Two commercial airliners were hijacked, and each was flown into one of the two 110-story towers. The Structural damage sustained by each tower from the impact, combined with the Ensuing fires, resulted in the total collapse of each building. In total, 10 major buildings experienced partial or total collapse and approximately 30 million square feet of commercial office space was removed from service, of which 12 million belonged to the WTC Complex.
The collapse of the twin towers astonished most observers, including knowledgeable structural engineers, and, in the immediate aftermath, a wide range of explanations were offered in an attempt to help the public understand these tragic events. However, the collapse of these symbolic buildings entailed a complex series of events that were not identical for each tower.
To determine the sequence of events, likely root causes, and methods or technologies that may improve the building performance observed, the Federal Emergency Management Agency (FEMA) and the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), in association with New York City and several other Federal agencies and professional organizations, deployed a team of civil, structural, and fire protection engineers to study the performance of buildings at the WTC site.
Although the team conducted field observations at the WTC site and steel salvage yards, removed and tested samples of the collapsed structures, viewed hundreds of hours of video and thousands of still photographs, conducted interviews with witnesses and persons involved in the design, construction, and maintenance of each of the affected buildings, reviewed construction documents, and conducted preliminary analyses of the damage to the WTC towers, with the information and time available, each tower could not be definitively the sequence of events leading to the collapse of determined. Because of lack of built-in monitoring system and there was not time to deploy an external one, it is unfortunate that the studies had to rely on some subjective information as well, in addition to field observations. Therefore, from our opinion, objective, uniform, scientific data is missing about what actually happened during the collapse of the WTC.
Let's remember that after September 11 similar attacks to high-rise buildings happened again inside as well as outside the US.
Unfortunately, terrorist attack is not the only threat to such structures. For example, if a high-rise building or a bridge is partly damaged in a major earthquake, the very first decision we need to make is whether the structure is still safe for rescue personnel to enter (in the case of a building) or for emergency vehicles to pass (in the case of a bridge) in order to carry out rescue work. A real-time monitoring system can function as an early warning system, will provide crucial data for making these decisions, and will help to establish the mechanism if the structure is collapsed.
A real-time system based on optical fiber and GPS sensors for monitoring structural integrity has been proposed in this paper.
CONCEPTUAL DESIGN OF THE SYSTEM:
In the designed system (Figure 1), there are 4 RTK GPS receivers atop the skyscraper on the vertices and 4 groups of several strings of optical fiber Bragg grating (FBG) sensors deployed along the 4 edges of the perimeters. The GPS sensors are used to measure the 3D positions of the vertices so that strain, tilt and rotation of the skyscraper can be determined. The vibrations of the skyscraper can be measured directly if an external reference GPS receiver is used together with the rover receivers atop the skyscraper at high sampling rate. The optical fiber Bragg grating (FBG) sensors are used to measure both strain and temperature. In the system 20 FBG sensors connected by optical fiber form one linear array (string) in which they are arranged in 10 pairs of 2 closely located FBG sensors. In each pair, one FBG sensor is in thermal contact with the structure but does not respond to local strain changes while the other FBG sensor responds to both temperature and strain changes so that temperature and strain changes can be discriminated. The length of optical fiber between two adjacent FBG sensor pairs is the same as the height of one storey so that there is one FBG sensor pair at each of the 4 edges on every floor. Hence, one string with 20 FBG sensors will cover 10 storey of the skyscraper. Therefore, depending on the total number of storey in the skyscraper, several strings of optical fiber Bragg grating (FBG) sensors will have to be used in each edge. Taking the WTC as an example, 11 strings have to be used at each edge in order to cover the entire storey.
Experiments have been carried out to study the feasibility of using the GPS and FBG sensors in such an integrated system.
THE GPS COMPONENT:
In a joint experiment in Tokyo on 10 August 1999 between the University of New South Wales (UNSW), Australia and the Meteorological Research Institute (MRI), Japan, two Trimble MS750 GPS receivers were Used in the RTK mode with a fast sampling rate of up to 20Hz (Ge 2000). As can be seen from Figure 2, the GPS antenna, an accelerometer, and a velocimeter were installed on a metal plate,
[attachment=20453]
INTRODUCTION:
The collapse of the World Trade Center (WTC) twin tower has caught many people by surprise and has reminded us of the importance of structural integrity monitoring for improving disaster preparedness and response. “Nobody thought it (WTC) would collapse!” The sentence has been repeated many, many times in the media on the first anniversary of 11 September 2001. The events following the 11 September 2001 attacks in New York City were among the worst building disasters in history and resulted in the largest loss of life from any single building collapse in the United States. Of the 58,000 people estimated to be at the WTC Complex, over 3,000 lost their lives that day, including 343 emergency responders. Two commercial airliners were hijacked, and each was flown into one of the two 110-story towers. The Structural damage sustained by each tower from the impact, combined with the Ensuing fires, resulted in the total collapse of each building. In total, 10 major buildings experienced partial or total collapse and approximately 30 million square feet of commercial office space was removed from service, of which 12 million belonged to the WTC Complex.
The collapse of the twin towers astonished most observers, including knowledgeable structural engineers, and, in the immediate aftermath, a wide range of explanations were offered in an attempt to help the public understand these tragic events. However, the collapse of these symbolic buildings entailed a complex series of events that were not identical for each tower.
To determine the sequence of events, likely root causes, and methods or technologies that may improve the building performance observed, the Federal Emergency Management Agency (FEMA) and the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), in association with New York City and several other Federal agencies and professional organizations, deployed a team of civil, structural, and fire protection engineers to study the performance of buildings at the WTC site.
Although the team conducted field observations at the WTC site and steel salvage yards, removed and tested samples of the collapsed structures, viewed hundreds of hours of video and thousands of still photographs, conducted interviews with witnesses and persons involved in the design, construction, and maintenance of each of the affected buildings, reviewed construction documents, and conducted preliminary analyses of the damage to the WTC towers, with the information and time available, each tower could not be definitively the sequence of events leading to the collapse of determined. Because of lack of built-in monitoring system and there was not time to deploy an external one, it is unfortunate that the studies had to rely on some subjective information as well, in addition to field observations. Therefore, from our opinion, objective, uniform, scientific data is missing about what actually happened during the collapse of the WTC.
Let's remember that after September 11 similar attacks to high-rise buildings happened again inside as well as outside the US.
Unfortunately, terrorist attack is not the only threat to such structures. For example, if a high-rise building or a bridge is partly damaged in a major earthquake, the very first decision we need to make is whether the structure is still safe for rescue personnel to enter (in the case of a building) or for emergency vehicles to pass (in the case of a bridge) in order to carry out rescue work. A real-time monitoring system can function as an early warning system, will provide crucial data for making these decisions, and will help to establish the mechanism if the structure is collapsed.
A real-time system based on optical fiber and GPS sensors for monitoring structural integrity has been proposed in this paper.
CONCEPTUAL DESIGN OF THE SYSTEM:
In the designed system (Figure 1), there are 4 RTK GPS receivers atop the skyscraper on the vertices and 4 groups of several strings of optical fiber Bragg grating (FBG) sensors deployed along the 4 edges of the perimeters. The GPS sensors are used to measure the 3D positions of the vertices so that strain, tilt and rotation of the skyscraper can be determined. The vibrations of the skyscraper can be measured directly if an external reference GPS receiver is used together with the rover receivers atop the skyscraper at high sampling rate. The optical fiber Bragg grating (FBG) sensors are used to measure both strain and temperature. In the system 20 FBG sensors connected by optical fiber form one linear array (string) in which they are arranged in 10 pairs of 2 closely located FBG sensors. In each pair, one FBG sensor is in thermal contact with the structure but does not respond to local strain changes while the other FBG sensor responds to both temperature and strain changes so that temperature and strain changes can be discriminated. The length of optical fiber between two adjacent FBG sensor pairs is the same as the height of one storey so that there is one FBG sensor pair at each of the 4 edges on every floor. Hence, one string with 20 FBG sensors will cover 10 storey of the skyscraper. Therefore, depending on the total number of storey in the skyscraper, several strings of optical fiber Bragg grating (FBG) sensors will have to be used in each edge. Taking the WTC as an example, 11 strings have to be used at each edge in order to cover the entire storey.
Experiments have been carried out to study the feasibility of using the GPS and FBG sensors in such an integrated system.
THE GPS COMPONENT:
In a joint experiment in Tokyo on 10 August 1999 between the University of New South Wales (UNSW), Australia and the Meteorological Research Institute (MRI), Japan, two Trimble MS750 GPS receivers were Used in the RTK mode with a fast sampling rate of up to 20Hz (Ge 2000). As can be seen from Figure 2, the GPS antenna, an accelerometer, and a velocimeter were installed on a metal plate,