A Feasibility Study of Building Structural Deformation Monitoring using Global Positioning (GPS) - Essay Example

?Summary and Critique A Feasibility Study of Building Structural Deformation Monitoring using Global Positioning (GPS), Terrestrial Surveying Technique (TST) and Crack Gauge Measurement (CGM) Summary: Through this paper, the authors attempted to assess the utility of geodetic surveys, which include conventional terrestrial surveys as well as satellite surveys using GPS (Global Positioning System), and geotechnical or structural surveys, like crack width measurements, for the monitoring of high and low-rise buildings. The authors’ main objective was to assess the advantages and disadvantages of these techniques. To achieve their objectives through this study, the authors monitored structural deformations in one high-rise building, viz. the Twin Tower of Science and Technology Complex, and one low-rise building, viz. the Innovation Centre Building, both of which belonged to the University Technology MARA (UiTM), in Selangor, Malaysia. The authors chose high accuracy GPS (±1 mm) and total station (± 1 mm, 1”) to apply in deformation monitoring of the buildings, to improve accuracy of the survey. During the course of the study, authors identified appropriate points on the building structure, and suitable control points around the building to begin the structural monitoring process. They then carried out GPS surveys using the rapid static technique, geotechnical surveys through crack-width measurements using the digital movement gauge, and terrestrial surveys using the intersection technique on the building structures for four epochs. In this study, the authors demonstrated that while crack width measurements using the digital movement gauge were helpful in identifying deformations occurring in one dimension (1 D), the intersection technique of terrestrial surveying is advantageous for monitoring the deformations that occur in two dimensions (2 D). However, the GPS survey was of no utility for monitoring the building deformations, as it did not provide consistent results. According to the authors, the inconsistency of results of the GPS survey was due to obstruction of the antenna that was to receive the satellite signal, by the surrounding building structures. The strength of this study lies in the fact that accuracy in survey methodology and results was maintained. The authors successfully demonstrated the use of various survey techniques in monitoring building structure deformation through appropriate and reliable data and measurements. The information on the efficiency of the various techniques in monitoring building structure deformation occurring in 1D and 2D will prove to be useful in choosing the appropriate technique based on individual building survey requirements. The weakness of this study, however, is that it suffers from lack of appropriate data analysis, as the objective, i.e. assessment of the advantages and disadvantages of the discussed techniques was not sufficiently met. Importance of the study: This article is significant as the authors assess the most prominent survey techniques and distinguish them based on their utility in deformation monitoring. The study will enable making a better a choice while choosing which type of survey technique is to be used when deformations occurring in 1D or 2D are to be monitored. This study also indicates that using GPS for monitoring deformations is futile in areas where surrounding high-rise buildings and obstructions exist, such as in cities. This paper provides concise methodology and distinct deformation monitoring techniques that will be helpful in carrying out deformation measurements for my project study. 2. Deformation Monitoring by GPS at Embankment Dams and Deformation Analysis Summary: The main objective of this study was to assess deformation at the crest of the Altinkaya dam, caused by a combined effect of the weight of the dam and the water load occurring at different water levels. A secondary objective was to investigate if GPS surveying technique and its measurements are accurate enough to be used for examining deformations occurring in the structure of a dam. Deformation monitoring of a dam is a top priority for examination of the security of the dam and shelter the lives and possessions of people living in its neighbourhood. For the purpose of this study, three dual frequency GPS receivers were used. A network of eleven object points and six reference points was constructed for deformation measurements, which were conducted four times in two years. To analyse data obtained from assessment of the movement at reference and object points in deformation measurements, the authors used the iterative weighted transformation method and the Fredericton method. The former method is applicable when no prior data is available on the displacement of points in the network, and the latter one can apply to any kind of geometrical analysis. Results from both these approaches were compared and analysed. All the equipment was calibrated before starting deformation measurements. Two different GPS network observations, the reference network and the object network, were performed in the survey. Data from the GPS survey was processed using the GeoGenius 2000 software. The authors confirmed from this study that although minute displacements were observed at the central part and the extreme ends of the Altinkaya dam due to water load, it was safe and was not a threat to the safety of the people living in its vicinity. A significant finding of this study is that GPS can be used for a two dimensional (2D) deformation analysis of dams. Inaccurate Z-component limited the results of the GPS used in this study to 2D. The main strength of this study is that the technique used enables the identification of unstable reference points in the reference network during deformation analysis. According to the authors, this will enable the selection of best minimum constraints and deformation models during the later stages of analysis. The shortcoming of the network is shortage of some GPS baselines with object points and reference points. The reliability of deformation monitoring surveying can be enhanced if the network contains sufficient redundancy, which could check and eliminate the observational and processing errors. Importance of the study: Protecting the structure of a dam can be immediately carried out once abnormal deformation in its structure is detected using appropriate techniques. Therefore, accurate methods of deformation analysis of dams are vital. The present study is critical since the process of deformation monitoring surveying of this study provides a distinct outline comprising the network design, surveying methods and approaches of data analysis. This study also proves the utility of GPS measurements in deformation monitoring of dams. The techniques used in this study will enable future insights into accurate analysis of deformation in dams. GPS measurements will be taken into account in my project as an important surveying method. 3. Progress in Deformation Monitoring for Dams, Bridges and Power Lines Summary: Deformation monitoring of structures is of extreme importance to ensure the safety of any construction. Most traditional deformation techniques have been replaced with satellite-based spatial technologies. In dangerous or inaccessible regions, satellite based techniques are being used for deformation monitoring. The present article discusses the use of satellite-based spatial technologies for deformation monitoring in different types of constructions– dams, river beds, power lines, bridges and high-rise buildings. Dam deformation monitoring using global navigation satellite systems (GNSS), which have several strengths such as rapid feedback of deformation, monitoring network configuration and dam design, wireless and other flexible communication links was discussed using the Geheyan hydropower station as an example. River bank deformation monitoring using virtual reference stations (VRS) was also discussed. A VRS system covers a large area and has numerous roving points that are sustained by reference stations. VRS monitoring of the Yangtze River banks was explained to provide a working example of the use of VRS in monitoring of extra-long linear structures such as rivers. Use of high-resolution synthetic aperture radar (SAR) images for monitoring the deformation of power lines present in inaccessible environments was also discussed. Physical changes in power lines can be detected using SAR images. Using the target-scattering properties of the transmission tower, SAR images can be obtained at all times and even under extreme weather conditions. The Sutong Bridge on the Yangtze River, which is the longest suspension bridge in China, was used as a case study to exemplify the use of GPS in combination with total station-based ‘georobot’ subsystem for monitoring bridge deformations. Finally, monitoring of deformation during construction of high-rise buildings was also discussed. Winding vibrations, incident angle of sunrays, deadweight and temperature discrepancies between the top and bottom floors cause deformations in buildings. These deformations can be detected using GPS systems. The Beijing CCTV new tower and the Shanghai Financial Centre are examples where GPS monitoring was used at construction sites. The strength of this study is the concise way in which the author has described the various kinds of applications of GPS technology in deformation monitoring of different types of constructions, and the suggestions given to cover blind areas that are not covered by GPS. However, this study suffers from the lack of sufficient data and data analysis, which is a weakness of this article. Moreover, the processes are described comparatively superficially and ordinarily, which is another shortcoming of this article. Importance of the study: This article is chosen as an important research paper because satellite-based spatial technologies are systematically illustrated in various applications for deformation monitoring of dams, river banks, transmission towers, bridges and high buildings. By condensing research on the five main construction structures and the feasibility of use of GPS technologies in monitoring them, the author has provided a brief yet rich resource of information. Including suggestions for overcoming the current shortcomings of these technologies for each type of construction in particular, especially focusing on possible alternatives for blind areas that cannot be monitored by GPS, this paper offers directives for future research, apart from stressing on present applications. 4. Monitoring of Bridge Deformation using GPS Technique Summary: Bridges are indispensable structures for transportation, and the inspection of bridges for structural safety has complicated technical issues. This paper demonstrates the characteristics of long and short-term deformations in suspension bridges and the merits of using global positioning system (GPS) in monitoring bridge deformation. The advantages of using GPS in bridge monitoring include the possibility of “all-time monitoring” even in inclement weather conditions, full time observation, automatic measurements, high speed monitoring and high precision of measurements and data processing. Another significant advantage is that since GPS depends on signals from satellites located in space, there is no need for visibility between the observation stations, and the data captured by each station are independent of one another. This article further discusses other requirements to be used in conjunction with GPS technology for bridge monitoring. These include preprocessing of the GPS signals for noise removal and filtering of useful signals through wavelet analysis, for further data processing. Kalman Filter (KF) and Parametric Least Square (PLS) are the two common types of wavelet analysis, and these are discussed further in this article. The outline of structural deformation monitoring system of the Yonghe Bridge is presented in this paper. Details of GPS data collection including the surveying network and GPS observations are also described. The Bursa-Wolf transformation method was used for transformation of GPS observations from global coordinates to local coordinates of the bridge. Two adjustment steps–KF and PLS were performed using the Matlab software. The cycle ambiguities and the detection and correction of cycle slips were performed in KF algorithms. The outcomes of the coordinate values from KF and PLS were very similar. SPSS statistical software was used to analyse bridge deformation. There are three key findings of this study. Firstly, traffic load played a major role in bridge deformation, and this was established through the KF method. Secondly, the maximum deformation occurred after six months of opening of the bridge, due to highest traffic load during mid span. The distance between this deformation and the beginning abutment was 48.2 m. This result was established through the PLS method. Finally, using the F-test, it was found that the south tower returned to its original condition after ten months of opening. An apparent weakness of this study is that there is only one reference station in the GPS surveying network. Consequently, deformation monitoring will be unauthentic due to base point instability. Another shortcoming is that only the south tower of the bridge was used for deformation studies. Importance of the study: I consider this paper critical as a thorough analysis of bridge deformation monitoring was done. This was reinforced using the Yonghe Bridge in China as a case study. This study confirms the accuracy of measurements using GPS and also discusses appropriate techniques for data processing and analysis. DGPS and RTK are presented as valuable tools in surveying techniques. One of the significant findings of this study is that the crack width on the abutment is greater than that on the mid span of the bridge. This study offers a concise plan of bridge deformation monitoring, and will be useful as a primer for further studies. 5. Fundamental Principles of Deformation Measurement Summary: The objective of this paper was to clarify basic principles and problems in deformation monitoring. Some surveyors are negligent about the importance of precision and other factors vital for deformation surveys, often ending up in damage to property and loss of life through improper deformation monitoring. Therefore, this paper demonstrates and discusses radical rules that underlie deformation monitoring, as this field is complicated and entails sophisticated work. The authors discuss five critical principles, which include understanding of the basic processes of the measurement in monitoring programmes, ascertainment of the importance of precision in results to ensure repeatability and reproducibility of data, design of appropriate measurement systems that fulfill the requirements and objectives of the survey, guaranteeing the stability of marks used during survey to ensure high precision and longetivity, and importance of appropriate sampling frequency. The authors discuss each of these five principles in detail, giving necessary examples and relating incidences that resulted from improper surveying and deformation monitoring. As this field involves an in-depth analysis of the structural changes occurring in a construction, an understanding of the underlying processes that are involved in causing the change is of utmost importance. This requires a multi-disciplinary approach. Furthermore, the authors assert that “measurement precision takes centre stage” in deformation monitoring. Since it deals with detection of change in the building structure, the reproducibility and repeatability (precision) of the measurements is vital. This is because monitoring requires frequent and periodic measurements under different conditions and at different times. Apart from the use of appropriate equipment, the design of an appropriate procedure is also critical to deformation monitoring. A well-designed and mathematically simulated system can predict the precision and reliability of results. Another aspect of surveying, namely the use of benchmarks and control points is also discussed. The authors write that in order to ensure the stability of marks taken during the survey, they must be taken in reference to an external reference system. Surveyors should ensure that the marks can withstand mishaps and are stable, enabling reproducibility of measurements with precision. Finally, the number of times a survey is performed and the sampling frequency should be reflective of the need of the particular structure. Negligence of each of the five principles and its consequence was discussed using independent examples from real life incidents. The only shortcoming of this study is that an elaborate discussion of methodologies was not dealt with, and authors agree that the subject is too broad and beyond the scope of the paper. Importance of the study: This article is vital for all those who are involved in deformation monitoring and surveying, as it deals with the most important issues in the field. Deformation surveying is different from other types of surveys because it comes with an extended responsibility. The surveyor has to ensure that nothing is being missed or neglected while taking measurements and analysing them, to ensure the safety of a structure. Failure to do so will not only result in damage to property, but also in loss of life. Following the five critical principles discussed in this article with dedication and responsibility is thus recommended. Read More