Correlation of the movements of the Severn Suspension Bridge derived with GNSS with temperature variations

In March 2010, four days of GNSS data were gathered on the Severn Suspension Bridge. The GNSS antennas were located on the tops of the four support towers, as well as five locations on the suspension cables. The Severn Bridge has a main suspended span of 998m long. The GNSS data were gathered at rates of 10Hz and 20Hz between the 10th to the 12th and on the morning of the 18th March 2010. In addition to the GNSS data, the air and steel temperatures were gathered every 10 minutes. The GNSS data were processed in an On The Fly manner relative to a reference GNSS receiver located on a solid building adjacent to the Bridge

Real time on-the-fly kinematic GPS

Considerable interest has been show in the development and application of real time On-The-Fly (OTF) kinematic GPS. A major error source and limitation of such a positioning technique is that caused by cycle slips. When these occur, the integer ambiguities must be resolved for, which can take hundreds of epochs to complete depending on satellite availability and geometry. This research has focused on investigating the applications of real time OTF GPS, as well as its limitations and precision, which has been shown in the thesis to be precise to a few millimetres. The limitations of such a system at present include the use of UHF telemetry links, which at best have a line of sight range of -10 km. The research has shown that alternatives are required, and the use of a relay station can prove invaluable. Cycle slips are another major limiting factor when using OTF GPS, as once a cycle slip occurs, it can either be corrected for or the integer ambiguities resolved for. The second option can take hundreds of seconds, depending on the algorithms used and the satellite number and geometry. This research has partly focused on the development of software which will instantaneously detect and correct for cycle slips in high rate GPS data. The applications of real time OTF GPS are numerous. Research has been carried out to investigate its use to monitor and control construction plant as well as monitoring the movement of large structures. As OTF positioning is precise to a few millimetres, it is ideal for the control of construction plant, and has been compared to laser levelling and precise digital levelling. Such a GPS system gives the user a 3-dimensional position for the bulldozer blade, for example. Such information can prove invaluable for quality control as well as developing an automated system, which would be controlled by real time OTF GPS. In addition, real time OTF GPS has been shown in the research to provide instantaneous positioning of large structures in the form of bridges. Such information could provide future systems which would monitor the structure for dangerous movements, resulting in a failure alarm. Carrier phase kinematic GPS has previously been shown to work over baseline lengths of < 20 km. The use of Multiple Reference Stations (MRS) has been shown in this research to enable OTF GPS to be applied over longer baseline lengths, with a precision in the order of 12 cm over 132 km

Real time on-the-fly kinematic GPS

Considerable interest has been show in the development and application of real time On-The-Fly (OTF) kinematic GPS. A major error source and limitation of such a positioning technique is that caused by cycle slips. When these occur, the integer ambiguities must be resolved for, which can take hundreds of epochs to complete depending on satellite availability and geometry. This research has focused on investigating the applications of real time OTF GPS, as well as its limitations and precision, which has been shown in the thesis to be precise to a few millimetres. The limitations of such a system at present include the use of UHF telemetry links, which at best have a line of sight range of -10 km. The research has shown that alternatives are required, and the use of a relay station can prove invaluable. Cycle slips are another major limiting factor when using OTF GPS, as once a cycle slip occurs, it can either be corrected for or the integer ambiguities resolved for. The second option can take hundreds of seconds, depending on the algorithms used and the satellite number and geometry. This research has partly focused on the development of software which will instantaneously detect and correct for cycle slips in high rate GPS data. The applications of real time OTF GPS are numerous. Research has been carried out to investigate its use to monitor and control construction plant as well as monitoring the movement of large structures. As OTF positioning is precise to a few millimetres, it is ideal for the control of construction plant, and has been compared to laser levelling and precise digital levelling. Such a GPS system gives the user a 3-dimensional position for the bulldozer blade, for example. Such information can prove invaluable for quality control as well as developing an automated system, which would be controlled by real time OTF GPS. In addition, real time OTF GPS has been shown in the research to provide instantaneous positioning of large structures in the form of bridges. Such information could provide future systems which would monitor the structure for dangerous movements, resulting in a failure alarm. Carrier phase kinematic GPS has previously been shown to work over baseline lengths of < 20 km. The use of Multiple Reference Stations (MRS) has been shown in this research to enable OTF GPS to be applied over longer baseline lengths, with a precision in the order of 12 cm over 132 km

Correlated GNSS and temperature measurements at 10-minute intervals on the Severn Suspension Bridge

Global Navigation Satellite System (GNSS) data were gathered on the 998-m-long Severn Suspension Bridge main span. The antennas were located on the tops of the four support towers, as well as five locations on the suspension cables; data were gathered at rates of 10 and 20 Hz. In addition, air and steel temperatures were gathered every 10 min. The GNSS data were processed in an On The Fly manner relative to a reference receiver located on a fixed position adjacent to the Bridge, and the resulting dataset was compared to the air and steel temperature data measurements, and correlations reported. Moving average filters that eliminate short-term movements due to wind loading and traffic loading were applied to the GNSS data, resulting in the longer-term deflections due to temperature changes every 10 min. The temperature over the 3 days varied by up to 10 °C, and movements of the order of decimetres were seen. Clear numerical correlations between the changes in temperature and the changes in height are presented when analysed at these 10-min intervals, suggesting that temperature compensation in structural health monitoring systems could be readily applied, resulting in a sustainable structure

Deflection Monitoring of the Forth Road Bridge by GPS

Researchers at the IESSG at the University of Nottingham, in conjunction with colleagues from Brunel University, have carried out deflection monitoring work on structures, notably bridges, for a decade. Initial work was carried out on the Humber Bridge, London\u27s Millennium Bridge and the Wilford Footbridge in Nottingham. These trials were carried out over a number of years, using a whole succession of GPS receivers. The initial trials showed that the use of carrier phase GPS could indeed allow sub centimetre movements to be detected, in addition to which, the frequencies of the movements could be calculated. Today, the authors are carrying out such work using state of the art dual frequency surveying grade code and carrier phase GPS receivers. The Forth Road Bridge has an overall length of 2.5 km, a main span length of 1,005m, and was opened in 1964. Traffic has steadily increased over this bridge, from 4 million vehicles in 1964 to over 23 million in 2002. In addition, the heaviest commercial vehicles weighed 24 tonnes; the current limit is 44 tonnes. When the bridge opened, it brought to an end an 800 year history of ferryboat service across the river at Queensferry. Such bridges experience traffic loading greater than that initially anticipated. The following paper details how GPS can be used to evaluate the performance of such a structure. On the 8 and 9 February 2005, a series of tests was conducted upon the Forth Road Bridge in Scotland. During the trials, 7 Survey grade GPS receivers were located upon the bridge, and a further two located as reference stations adjacent to the structure. In addition, a high accuracy Applanix INS, POS-RS, was also located upon the bridge; this is the subject of another paper. Of the 7 receivers on the bridge, four were located at the 1/8, 1/4, 1/2 and 3/4 span on the East side of the deck, whilst a fifth was located at the 1/2 span on the west side of the bridge. A further two receivers were located on top of the two towers at the south end of the bridge. All the receivers gathered data, almost non-stop, for a 48 hour period, at a rate of 10Hz or 20 Hz. Leica 530, 510 and GPS1200 receivers were used during the trials. During the trials, a weather station was used to gather the wind speed and direction, as well as the temperature. This could then be used to evaluate the total force i.e. wind and traffic, experienced by the bridge. During previous trials upon structures, the 10Hz GPS data has been densified with accelerometers capable of gathering data at up to 1,000 Hz. However, as this structure is so large, such high speed movements were not expected, and hence no accelerometers were used, and only the INS. The Ordnance Survey of Great Britain has 74 active station GPS receivers located around the UK. These stations gather data at 1Hz, but then the data is made available at a 15s epoch rate to the public via their web site. In addition to this, the OS are currently establishing their own Network RTK system in the UK. During the trials, the GPS data from a number of OS stations located adjacent to Edinburgh were gathered for the IESSG in order to use these as a comparison with the bridge data processed relative to the reference stations next to the bridge. During the trials, gusts of up to 60 mph were experienced, and the traffic loading was very heavy, especially at rush hour times. In addition, during the trials, a 100 tonne lorry passed over the bridge, and a series of trials were carried out with two 40 tonne lorries, equipped with DGPS to ascertain their locations, and having the bridge closed to other traffic. This is the most controlled of all the trials, as the wind loading is known from the weather station and the only traffic present on the bridge are the two 40 tonne lorries. The expected movements were calculated from the FEM, and the true results compared very well to these. Further to this, during the trials, IESSG staff took shifts to occupy the points, sitting in cars whilst the GPS receivers gathered the data to post-process in an On The Fly manner. During the data gathering exercise, it was evident that the bridge did move, and it was also possible to see a rippling effect on the bridge deck. On processing the data, movements of almost a metre were seen and the rippling effect was evident in the data as well. The results are compared to finite element models (FEM) that exist of the bridge. The 3D coordinates available from the GPS results were transformed into frequencies of the structure\u27s movements. These frequencies and magnitudes of the movements compared very well with the FEM. The following paper details the trials, as well as the post processing techniques carried out on the single and dual frequency carrier phase data. The results are given for all the locations upon the bridge, showing how the bridge moves over a 46 hour period with a variety of loading. Further to this, detail is given on how the GPS results were compared to the FEM, and how such results can indeed be used for structural health monitoring. Reprinted with permission from The Institute of Navigation (http://ion.org/) and The Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation, (pp. 1016-1021). Fairfax, VA: The Institute of Navigation

Temperature effects on the vertical movements of the Severn Suspension Bridge’s suspension cables measured by GNSS

The use of GNSS for the deflection monitoring of large bridges has been an ongoing field of research for 20 years. The Severn Suspension Bridge, in the UK, has a main span length of 988 metres. Datasets were gathered in both March 2010 and July 2015 by placing GNSS antennas on the tops of the support towers, as well as on the suspension cables. The data were gathered over four days and three days respectively during these surveys. In addition to the GNSS data, weigh in motion data of the traffic loading, the temperature of the bridge’s steel work, and the air temperature and wind speed and direction at a number of locations were collected. In 2010, the temperature during the survey varied between 0.335ºC to 13.750ºC for the air temperature, and between 0.886ºC to 12.390ºC for the steel temperature. During the survey in 2015, the temperature for the air varied between 10.800ºC to 22.160ºC, and the steel temperature varied between 13.820ºC to 20.410ºC. This paper analyses the vertical movements at the mid span of the bridge’s suspension cable using the data from 2010 and also 2015. The vertical movements are due to a number of reasons. Firstly, the traffic flow will cause rapid changes in the height of the cable, of the order ofdecimetres due to changes in traffic loading over a time period of seconds or minutes. Secondly, the wind will also cause movements in the cable, but mainly in the horizontal direction. Vertical movements due to the vibrating nature of the cable will also be present, at a rate of 0.1Hz or so. Finally, the cable will expand and contract due to the change in temperature. This will take place over a period of tens of minutes. The relation between the antenna location in 2010 and 2015 are calculated against changes in temperature, and correlation between the movements are shown. The overall movements due to the change in temperature during the survey in 2010 can be shown to be of the order of decimetres, and similarly in 2015. The change in a bridge’s height, due to a change in temperature is an important parameter to be known. A bridge in the UK could experience changes in temperature from almost 30ºC to -10ºC in a period of a year during its lifetime. In other parts of the world, this differential could be even more. This could result in a very significant vertical movement of the bridge, which in turn could affect the clearance space under the bridge for passing ships. This type of movement tied with changing tides could result in large ships colliding with such bridges if the clearance is not fully understood

A set-covering model for a bidirectional multi-shift full truckload vehicle routing problem

This paper introduces a bidirectional multi-shift full truckload transportation problem with operation dependent service times. The problem is different from the previous container transport problems and the existing approaches for container transport problems and vehicle routing pickup and delivery are either not suitable or inefficient. In this paper, a set covering model is developed for the problem based on a novel route representation and a container-flow mapping. It was demonstrated that the model can be applied to solve real-life, medium sized instances of the container transport problem at a large international port. A lower bound of the problem is also obtained by relaxing the time window constraints to the nearest shifts and transforming the problem into a service network design problem. Implications and managerial insights of the results by the lower bound results are also provided

Benefit of triple-frequency on cycle-slip detection

At the time of writing, all the Global Navigation Satellite Systems (GNSS) support or are designed to support triple- or multi- frequency, which is expected to have advantages over single- and dual- frequency. This paper will conduct research on how triple-frequency can benefit the cycle-slip detection process. Correctly detecting and repairing cycle slips can help extend the latency of the fixed ambiguities, estimate the ionospheric delay, reduce the measurement noise and finally improve the positioning precision of the carrier phase. This paper will firstly review the widely used cycle-slip detection methods, including high-order phase differencing, Doppler integration and the ionospheric residual. For applying triple-frequency in cycle-slip detection, we will modify the Hatch-Melbourne-Wübbena combination to eliminate the effect of the ionospheric bias and reduce the measurement noise on the detection value. The triple-frequency method can detect and correct cycle slips instantaneously. All the mentioned methods will be tested using triple-frequency Galileo data observed in static condition. The results show that the performance of the triple-frequency method has a higher success rate and a lower missed detection compared to those using single-frequency, especially in detecting small cycle slips in observation with large intervals. Although the ionospehric residual provides higher success rates at low elevation angles, the triple-frequency method is more advanced than the ionospheric residual, which cannot decide the magnitude of the cycle slips easily

Change detection and assessment of fire-damaged concrete using terrestrial laser scanning

Fire is one of the serious potential hazards to most structures and damage assessment is the first and the most important job for structural safety evaluation of a structure subjected to fire. The extensive use of concrete as a structural material has neccessitated an investigation into more robust and cost-effective techniques for the assessment of fire-damaged concrete using terrestrial laser scanning. Although concrete is known to be a fire resistant structural material, it undergoes severe changes when exposed to elevated temperatures and this can affect the load bearing capacity of structural bearing elements in several ways. Apart from spalling, there can be a permanent loss of strength in the remaining material. In the aftermath of a fire on a structure, various workers get involved in a variety of response and recovery from disaster operations. Furthermore, following a catastrophic failure of a structure after a fire, rescue workers and emergency responders may be required to enter the fire-damaged structure which can be risky and so an assessment method which has the potential to improve safety was investigated. Within the field of structural and civil engineering, the methods employed in assessing fire-damaged concrete involve both field and laboratory investigations to determine the extent of fire damage in order to design appropriate and cost effective repairs or to decide whether to demolition the structure. Concrete structures show significant loss of strength when heated above 300ºC. This study aimed at investigating whether terrestrial laser scanning can be used to detect fire-damaged concrete using specimens heated up to 1000ºC as it is important to estimate the maximum temperature attained in a fire. The results obtained from the study clearly demonstrated the feasibility of using terrestrial laser scanning to detect fire-damaged concrete via modelling and analysis of laser returned intensity. Laser scanning has emerged as a complementary assessment method of fire-damaged concrete with a couple of advantages in that the whole concrete element can be scanned and an average intensity value over the area concerned can be determined which would represent the whole element overcoming the challenge of some traditional methods where cores are drilled in limited areas. Scanning is rapid with millions of points measured in a few seconds. Laser scanning of the fire-damaged structure can be done from a distance without having to enter the structure and this improves safety. Laser scanning is a non-destructive technique for detecting fire-damaged concrete

A non-destructive technique for health assessment of fire-damaged concrete elements using terrestrial laser scanning

Concrete structures are routinely monitored to detect changes in their characteristics in the field of engineering surveying and other disciplines such as structural and civil engineering. There is growing demand for the development of reliable Non-Destructive Testing (NDT) techniques for concrete structures in the assessment of the deteriorating condition of infrastructures or in an event of fire-damaged structures. In this paper, the feasibility of using Terrestrial Laser Scanning (TLS) technology for change detection and assessment of fire-damaged concrete has been investigated through measurements and analysis of laboratory size concrete specimens that underwent heating up to 1000°C. The TLS technique employed in detecting fire-damaged concrete involved modelling and analysis of the TLS intensity returns as well as RGB image analysis. The results obtained clearly demonstrate the feasibility of using TLS to detect fire-damaged concrete. Although the laser scanners used in the study have different wavelengths, the results obtained in both cases are promising for a detection technique of fire-damaged concrete structures