GeoSHM (GNSS and Earth Observation for Structural Health Monitoring) is a Structural Health Monitoring (SHM) system that integrates GNSS and Earth Observation technologies to offer an integrated solution for the maintenance of different types of asset. GeoSHM will provide users with real-time measurements of their assets during normal and abnormal loading conditions. It will also provide a complete picture of the structure in its changing landscape, identifying threats caused by environmental conditions, land motion, engineering works, landslip, mining and industrial activity.
The objective of the study is to determine the technical feasibility and economic viability of the integrated use of multiple space assets for the structural health monitoring of bridges.
GeoSHM will provide the following information to the end users:
- Real-time 3D displacement and acceleration data streams at key locations on the structure using GNSS;
- Precise synchronisation of terrestrial sensors with GNSS time tags using fibre-optics;
- Slow subsidence characteristics of the supporting structures provided by satellite Interferometric SAR (InSAR) data;
- Estimates of long-term bridge motion, such as affected by thermal expansion, using integrated GNSS and InSAR data;
- Deformation estimates of a wide area of land surrounding the bridge using an integrated GNSS and InSAR solution.
Users and their needs
GeoSHM is a system that will appeal to a multitude of infrastructure operators and owners. In order to maximise the potential impact of the system and also its attractiveness to the target markets, it is essential that a range of stakeholders are engaged. Involving users and stakeholders ensures that proposed GeoSHM is functional and accurate. Users and stakeholders include: highways agencies, transport and bridge authorities/owners, maintenance service providers and Original Equipment Manufacturers (OEM).
Specific users/stakeholders include:
- Bridgemasters and Infrastructure Managers
- Forth Road Bridge
- Humber Bridge
- Yangtze River Bridge
- Engineering and Maintenance Contractor
- Flint and Neill
- Telespazio VEGA UK Ltd
- Transport Research London
- Smithers Purslow
- Leica Geosystems
- Public Authority
- London Borough of Hammersmith and Fulham
- London Highways
- Dissemination, Media, Industry Bodies & Networks
- National Physical Laboratory
- Critical Software
Feedback from individual use cases and the output of the user/stakeholder workshop have emphasised several user needs. The following are the most prominent:
- Reduce the cost of bridge maintenance by implementing a more targeted approach to inspections.
- To implement an automated, practical and cost-effective solution to assess the FRB's operational conditions and identify potential structural damage.
- To generate deflection data that provides more accurate guidance as to pinpoint necessary refurbishment, and thus avoid huge unnecessary costs.
- To install a monitoring system that can be integrated with existing monitoring technologies, allowing for cost savings, and wider monitoring potential.
- The need to design data collection and handling with a specific focus on who this data is destined for, and how it will be used.
Service/ system concept
The GeoSHM service will consist of:
- Data collection from multiple on-bridge sensors
- Time synchronisation of data
- Collection and processing of InSAR images for deformation monitoring:
- Large area environmental overview
- Input for post-event analysis, long term monitoring and SHM
- Data processing: Resulting in bridge deformation information
- Delivery of information to end users:
- Real-time SHM, and early warning of structural issues
- Post-event analysis of bridge behaviour for engineers and bridge operators
Space Added Value
The use of GNSS in SHM is commonplace, although the utilisation of its strengths is not high. The GeoSHM project will develop this aspect to make GNSS positioning a cornerstone of SHM. EO technology will be exploited to provide a thorough environment overview of the structural health of long span bridges and better define the expected maintenance schedule.
Current monitoring systems based on GNSS positioning present limitations when they are used to monitor long and flexible structures such as bridges. The limitations are due to: the high unit price of the COTS receivers, the relatively low and unstable positioning accuracy, the frequent signal blockage, the high level of multipath and the uncorrected residual tropospheric delay. Other conventional monitoring tools including accelerometers cannot provide direct geometric displacement information and the interpreted position drifts over time. Other force measurement tools and sensors fixed to bridges such as strain gauges are often more costly, complex to install and maintain and require frequent calibration. GeoSHM will integrate and use the complementary advantages of each individual sensor or system is proposed.
The benefits posed to the user are:
- Enhanced awareness of the maintenance requirements (quantifiable).
- Targeted maintenance
- Increased maintenance intervals
- Early warnings
- Emergency warnings
- Lowering the maintenance costs (via above benefits).
- Measuring the performance of structural design models against the real world performance.
- Identifying structural failures promptly.
Monitoring of the structure 24/7.
The GeoSHM system will provide bridgemasters with essential quantitative information that are useful to extract critical parameters about the safety conditions of their bridges and help them schedule cost-effective maintenance.
The proposed system will be directly linked to the computers of bridgemasters and maintenance engineers to conduct 24/7 monitoring of the health status of the bridge without physically accessing the infrastructure. The system is expected to be particularly useful for safeguarding bridges when they experience extra loads such as under high winds, extreme tides, temperature changes and unusual traffic loading.
The figure below shows the proposed architecture of GeoSHM: the GNSS information is gathered by receivers on the bridge and combined with GNSS information from reference receivers. Through secure internet connections this information is passed to the Central Processing Facility (CPF) where it is combined with EDAS (EGNOS Data Access Service) services and passed on to the Control Centre (CC). In the CC, the GNSS data are integrated with the data collected by the bridge sensors (e.g. accelerometers, wind sensors, etc.) to generate relevant bridge deformation measurements.
At the CC, an integration with InSAR products will also be performed. InSAR measurements have proven to be useful in identifying subsistence in the area surrounding the bridge and in providing critical information on the displacements and thermal responses of important substructures of the bridge such as supporting towers and cables.
The combination of GNSS data and InSAR measurements will provide a complete picture of the bridge deformations with a high temporal and spatial resolution.
Current structural health monitoring systems on long span bridges are not typically designed by the end user, and often drawn together from a number of different purposes. The following are the key issues that need to be addressed:
- Converting data into useful information for the user.
- Synchronising all monitoring sensors to the correct time.
- Effectively integrating InSAR monitoring into an SHM system.
- Protecting any system from vandalism/tampering.
- Structuring the system to make it attractive to the relevant purchasing organisations. Making any system affordable and cost effective.
The GeoSHM Feasibility Study has been successfully completed and its final review meeting was held on 12 March 2015. During this final meeting GeoSHM consortium summarised the achievements and discussed the existing issues and lessons learnt. They had also presented their plan to develop GeoSHM into the next stage.
During the GeoSHM FS a monitoring system that consists of dedicated communication system, four permanently installed GNSS receivers and three anemometers have been installed on the Forth Road Bridge (FRB). The installation on the FRB will stay for further test during demonstration project. Synthetic Aperture Radar images have been acquired of the surrounding area of the FRB and analysed with UNOTT’s in-house software pack PUNNET, which won the Copernicus Masters award in 2014.
It has proven that even with a limited monitoring system the Bridgemaster of the FRB could fully understand the loading and response effect under normal loading conditions and can also easily identify unusual deformations when there were extreme weather conditions.
EO data have proved to be extremely useful and confirm that over the years there are no significant movements on the supporting towers and surrounding areas. When analysed in China, EO images have shown ground subsidence around bridge sites located in two mega cities – Shanghai and Wuhan in China, that was caused by the underground engineering and water extractions.
During GeSHM FS two stakeholder workshops had been held to identify the end-users real needs and requirements which are fully reflected in the designing of the monitoring system that not only produces data but most importantly generates essential information for bridgemasters to assist them for decision-making practice The workshops were also used to disseminate the preliminary findings of GeoSHM FS. In September 2013 UNOTT organised an international deformation monitoring conference – JISDM 2013 that was attended by more than 200 people to promote GeoSHM which has attracted many potential users/stakeholders attention. Following the workshop, a Chinese bridge owner (BRDI) will join the next stage of GeoSHM development.