BOAS – Bâtiment Ouvrage d´Art Services

Bridges, Viaducts and Engineering Structures Under Close Supervision with HBM Strain Gauges and Transducers

Founded in 1989, BOAS (Bâtiment Ouvrage d’Art Services) is a consultancy firm specializing in the monitoring and control of engineering structures and buildings. BOAS engineers and technicians provide their expertise for everyday and more exceptional structures around the world.

To prevent accidents, such as bridges or viaducts collapsing, BOAS closely monitors all structural builds during each project. For this vital task, the choice of instrumentation is crucial, as it must provide highly accurate data. And for BOAS, it is also extremely important to have the support of experienced partners and top-class equipment – especially in the field of extensometry.

Challenge

To prevent accidents, such as bridges or viaducts collapsing, the progress of exerted stress has to be monitored, deformation during construction and reconstruction has to be measured, the progress of stress (or deformation) during the installation of support components has to be controlled, etc. The choice of instrumentation is crucial, as it must provide highly accurate data.

Solution

BOAS needed the support of experienced partners and top-class equipment – especially in the field of extensometry, and, therefore chose to collaborate with measurement specialists, HBK, a renowned provider of reliable measurement tools. HBK recommended HBM’s LS31.6/350 strain gauge for structural monitoring. For data acquisition, the QuantumX MX1615B strain gauge amplifier was determined to be the best choice for this kind of operation.

Result

QuantumX MX1615B conditioners, synchronized with a QuantumX CX22B of the same range, were used for remote data storage and transfer via a protocol. An additional benefit for the monitoring activities was that several adjustments and settings could be optimized directly, on the measuring unit, via the Ethernet connection to a host computer or remotely via 4G wireless connection.

BOAS and HBK: A Partnership Approach

Taking all requirements into consideration, BOAS chose to collaborate with measurement specialists, HBK, a renowned provider of reliable measurement tools and complete measurement solutions. As a bonus, HBK’s international engineering team were also able to offer the technical support BOAS needed.

HBK supplied BOAS with tools, such as strain gauges and data acquisition systems (including T probes), which met BOAS’ specific needs for over-monitoring of concrete, metallic and composite structures. HBK engineers also helped BOAS’ technical team with the installation of the systems.

Within the scope of its monitoring activities, BOAS must consider the requirements of civil engineering. These include:

Monitoring the progress of exerted stress
Measuring deformation during construction, reconstruction, or repair of engineering structures
Checking and validating of the existing calculations, to optimize the human resources immobilization during construction periods or compliance interventions
Controlling the progress of stress (or deformation) during the installation of support components
Checking the stability of the unit following different interventions and during mandatory final tests

The combination of high-precision instrumentation, a complete range of sensors (resistive, piezo-resistive/electrical or optical) and engineering services, convinced BOAS that HBK´s expertise would help them successfully complete all projects.

Strain Gauges: A Must-have!

Strain gauges are key elements for structural monitoring. Whether used directly on metal or cement structures, HBM’s models offer many advantages, including long-term stability.

As well as providing high measurement accuracy, the strain gauges have to remain operational throughout the entire construction period, including up to the first years of application (for example, a bridge investigation).

The measurement quality remains uncompromised over time and calibration is not required.

In order to optimize the instrumentation on steel structures, HBK’s Senior Project Engineer, Pascal Chaffot – responsible for the construction sites – recommended HBM’s LS31.6/350 strain gauge. Typically used for offshore platforms, this particular version is micro-welded to the structures. Equipped with HBK protection, its resistance over time is unmatched, even in extreme weather conditions.

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Data Acquisition System: Versatility and Reliability

As for data acquisition, HBK’s objective was to offer BOAS a system that could support all types of gauges (with nominal resistances of 120 Ω, 350 Ω, and 700Ω), all mounting systems (¼ bridge, ½ bridge), and the full bridge. It was decided that the MX1615 strain gauge amplifier, from HBM´s QuantumX range, was the best choice for this kind of operation.

The module can also support measuring channels for PT100Ω probes, which is useful to compensate for significant temperature variations, often the case for this application during the successive operation phases.

The converter’s 24 bits and perfect signal conditioning offers unique measurement precision. Using the same instrumentation, it can capture small amplitude phenomena (a few tenths of µm/m) and other measurements during final tests.

On the subject of unprotected environment gauge instrumentation, Carola Corazza, Head of Engineering Services for HBK Southern Europe, explains: “If the signal from a gauge is weak and not properly conditioned, electrical and/or electromagnetic disturbances can seriously affect the reliability of strain measurements.”

Carola continues: “For these kinds of situations, the Quantum MX1615B allows not only the optimization of signal filtering, but also the supply of DC or carrier frequency to the gauges. Knowing that the signal from this type of sensor is in MV/V – and therefore directly dependent on the quality of the power supply – we are fully aware of the importance of a multitask strain gauge bridge, such as the QuantumX MX1615B.”

The QuantumX MX1615B conditioners, synchronized with a QuantumX CX22B of the same range, allows for remote data storage and transfer via a protocol defined by the BOAS teams. This conditioner model can also easily create measurement ‘tasks’ in which to configure the measurement according to user requirements.

It also offers an additional advantage for monitoring activities: several adjustments and settings could be optimized directly, on the measuring unit, via the Ethernet connection to a host computer or remotely via 4G wireless connection.

HBK Services: Recognized Expertise

The HBK engineering team supported BOAS on site, helping them to obtain a clear understanding of structural health, which is crucial to ensure the safety and longevity of structures and buildings.

This work, a close collaboration between BOAS engineers and HBK’s Engineering Services team, included:

Take-over of the structure
Definition of appropriate instrument points
Preparation of relevant surfaces
Installation of strain gauges
Cable pulling to the data acquisition system
Setting of parameters before implementation
Training BOAS in the use of the instrumented system

With over 50 years’ experience and know-how in the instrumentation domain, HBK’s expertise within the test and measurement industry is globally recognized.

A Partnership Under the Banner of Efficiency!

Mr. Jonathan Barbut, Managing Director BOAS, sums up his satisfaction with our collaboration: "The choice of a single supplier for all services, as well as the supply of sensors and electronics, is an advantage in terms of time and reliability. The work we do with HBK´s service engineers - performed with precision and accuracy - is extremely efficient. These measurements are crucial for optimizing both the safety and lifetime of the structures we are working on. HBK has proved to be an indispensable partner for carrying out our monitoring tasks.”