We offer inspection tools for cables, bars and tie rods to assess structural pathologies and help preview the residual life of cable-stayed and prestressed structures.
Our solutions provide stress and strain measurement and detect hidden defects, such as age-related corrosion and other failures, before they become visible.
The measuring device is an annular capacitive probe, made up of two electrodes forming a capacitor, whose capacitance depends on the dielectric characteristics of the materials inside the cable’s polyethylene sheath.
The monitoring device, which completely surrounds the sheath, is moved along the cable to detect injection anomalies. Escan technology was developed in partnership with Cerema.
The patented Uscan technology, co-developed with UGE, is the only technology that can assess the condition of guy wire strands in the sensitive anchorage area. The technique uses an ultrasonic transducer pressed against the end of a wire by an operator. The “pulse-echo” principle, commonly used in non-destructive testing, is applied here with a wave guided along the wire to detect the presence of defects over a distance of several tens of centimeters. As soon as the wave encounters a discontinuity (partial or complete loss of wire section), an echo is generated in return and signal analysis allows the detection and approximate location of the defect.
The vibration frequency of a cable is linked to its tension. The method involves recording the cable’s natural frequencies and using them to estimate its tension. The calculations are made by assimilating the vibration of the cable to that of a vibrating string. The frequencies are obtained by manually vibrating the cable or by recording its natural vibrations.
This method is particularly useful when it is not possible to measure the force by weighing at one of the cable anchors. It is also commonly used to qualify shock absorbers installed on guy wires.
The 4DVib solution uses the principle of interferometric radar to measure the dynamic displacement of one or more points in its line of sight. This solution is easy to deploy on site and quickly provides the vibration level of a structure, determines its dominant vibration modes, or qualifies excessive deflection when a load passes.
The flexibility of this tool makes it very useful for accepting a structure (vibration acceptance criteria) or for checking its suitability for service. The tool can also be used to remotely estimate the tension of structural cables thanks to the simple relationship between the natural frequency and the tension of a cable.
Acoustic detection of broken wires in stay cables
When an individual wire or strand in a stay cable breaks, it emits a shock wave that propagates along the cable.
Acoustic monitoring involves detecting this wave using sensors positioned at the cable anchors or, if applicable, at the suspension collars. This network of sensors enables the location of the break along the cable to be determined by triangulation.
This method consists of determining the existing tensile force in a tie rod or bar with a free length, by measuring the force required to cause its head to detach from the anchor plate. It is governed by the TA 2020 guide for active tie rods.
The weighing operation is carried out using a jack, a hydraulic power unit, force and displacement sensors, and parts adapted to the various anchor heads (threaded heads, serrated heads, smooth heads) or prestressing bars that may be encountered.
The tension is obtained by exploiting the force/displacement measurement curve during the loading and unloading phases.
Upus® can be used to check the durability of structural reinforcement or connections made using prestressing bars. Prestressing bars are widely used to assemble components or to ensure structural strength. The release of forces in these bars can lead to critical structural risks. It is therefore necessary to periodically check that the forces applied remain acceptable.
The Upus® technique uses ultrasonic wave propagation to measure the stress in the bars. An ultrasonic transducer/receiver is attached or applied to the end of the bar. The Upus® measurement is taken from one end of the bar and can therefore be applied to bars where only one end is accessible.
Single-toron load cells are designed to continuously measure the force in guyed cables, both during tensioning and over the long term. They fit perfectly into the anchor covers of modern Freyssinet-type guy wires and are resistant to hot wax filling. Laboratory and field tested, they offer reliability, precision and durability, even at -40°C.
Sensors allow continuous monitoring of the forces in the strands. The total load of a guy wire is obtained by multiplying the load per strand by the number of strands.
A portable reader is available for each conditioned signal output.
Measuring changes in stresses in a structure is a common engineering need, as it enables us to verify the response of a structure to the stresses to which it is subjected. We offer a wide range of solutions:
The name ‘strain gauge’ is somewhat of a misnomer, as it measures micro-strain, which can then be converted into stress, provided that the Young’s modulus of the material is known.
Another name known in France for the same sensor is ‘vibrating string extensometer’.
It should be noted that it is possible to calculate the fatigue of certain materials on the basis of stress cycles accumulated over time, in order to estimate the residual service life. An example of an application is the monitoring of orthotropic metal slabs for bridges.
Finally, it should be remembered that the sensors only measure variations in stress relative to the day of installation. Other techniques exist for measuring historical stresses, such as the flat jack or Slotstress, the central hole method, etc.
Our solutions facilitate proactive decision-making so that you can: