3D Precision Structural Sensing system

Introduction

As structures reach (and eventually exceed) their design life it is often necessary to introduce enhanced monitoring to demonstrate that the structure remains well within safe tolerances.

Often parts of the structures (e.g. bridges, tunnels, dams etc.) are relatively inaccessible and hence any sensor systems need to be easy to install, suitably rugged and have a long service life. The monitoring employed needs to be able to identify problems often hidden within structures before they become serious. Near real-time monitoring of movements between components of the structure allows assessments of the overall performance of the structure and to predict its durability and remaining life.

Tenet were tasked to undertake development work to provide the “Proof of Concept” for a sensing system to detect sub-millimeter movements in components of a large civil structure. Many commercial systems only sense in a single dimension, however the customer required simultaneous real-time 3-Dimensional structural monitoring, which precluded the use of many existing commercial measurement systems.

Services Provided

Tenet provided the Design, Engineering and Development Services to deliver the “Proof of Concept” including:

  • Identification and selection of suitable measurement techniques to provide the desired precision and measurement stability across a range of harsh environmental conditions;
  • Design and Development of a robust sensor mounting arrangement with shallow fixings to avoid any potential to contact with the existing structural reinforcement;
  • Development of an experimental test rig and associated software data capture system;
  • Preparation of test strategies to demonstrate the sensor being utilised through a range of 3Dimensional movements with live recording and processing of measurement data;
  • Management and supervision of sub-contractors undertaking the testing;
  • Demonstration of the prototype system to the customer team and ultimate client.

Challenges

In this particular instance there were several bounding conditions which precluded the use of many standard / existing proprietary (COTS) solutions including:

Technically, there were a number of novel challenges:

  • The system must provide real-time 3Dimensional sub-millimeter measurements;
  • The health monitoring system must not have any adverse effects on the integrity of the existing structures, particularly with respect to any sensor fixing arrangements;
  • Due to site environmental conditions the time for installing or changing mounting brackets and / or sensors must be minimised, as must any maintenance or calibration periods;
  • The system must be rugged, provide a simple operator interface but also collate data for off-line scientific analysis to determine any long-term patterns or trends;
  • The measurement technique must be reliable, suitably sensitive to structural movements but insensitive to other influences such as cable length or environmental changes particularly temperature.

Tenet were responsible for identifying candidate measurement techniques and down-selecting to the most suitable overall technique bearing in mind the required measurement precision; environmental factors; fixing techniques; etc.

Tenet devised a set of evaluation tests to demonstrate key parameters including:

  • Fixing time and changeover time of mounting brackets on hardened concrete components;
  • Sensor installation and configuration time;
  • Measurement accuracy and repeatability to better than 0.1mm and ideally to 0.01mm

A specialist sub-contractor was used who had experience in the application of measurement systems on large civil structure but were not familiar with the quality systems and rigorous underpinned evidential approach used within some highly regulated environments. Working collaboratively, Tenet supported the sub-contractor and guided them through the deliver process. This included help with Quality Plans, Evidential Processes and Technical Reports.

Delivery

Many traditional sensor systems work in the amplitude domain and are therefore sensitive to changes in cable length, increases in joint resistance, or corruption by EMC/RFI. Tenet selected a frequency domain technique (Vibrating Wire Strain Gauges) which is insensitive to cable length and joint resistance. Using VWSGs simplified the maintenance and calibration requirements.

A 3-Dimensional mounting arrangement was developed which included special features to simplify installation and securely retain the VWSG sensors as any sensor slippage would be erroneously reported as a structural movement.

The test system was constructed to allow fixing of the 3-Dimensional sensor mounting arrangement to be demonstrated.  Part of the test system was a fixed concrete component and another component could be moved in very small increments using a hydraulic ram to demonstrate the sensor response.  A manual reference measurement system was also attached so that displays of actual movement could be observed and recorded.

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Conclusion

Tenet developed and delivered the “Proof of Concept” for a high precision and very sensitive 3Dimensional sensor system.

A comprehensive feasibility study and performance report was produced to record the work development work. A large ultimate client team witnessed real-time demonstrations of the system, with operatives fixing sensors; structural components being moved in real-time and results being recorded and displayed. The ultimate client team included several functional experts in Engineering (Mechanical, Civil, Instrumentation, Systems, Software) together with representatives of Technical, Projects and Operations.  The “Proof of Concept” was successfully demonstrated to the satisfaction of our customer and ultimate client teams.

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Electrical

Contact Janine on 01925 377933 Janine.Rudenko@tenetconsultants.co.uk

Mechanical

Contact Craig on 07739 654926 Craig.rogers@tenetconsultants.co.uk

Projects

Contact Kate on 01925 377938 Kate.McDermott@tenetconsultants.co.uk