Monitoring, Instrumentation, and Diagnosis
This theme is dedicated to the development and evaluation of inspection, instrumentation, and diagnostic techniques for existing structures. The laboratory's activities focus on assessing control or monitoring methodologies for the most critical and least accessible points encountered on-site based on feedback (cable anchoring, inspection of inaccessible cable parts, evaluation of pre-cracking fatigue damage, inspection of bonded joints to detect adhesion defects, etc.).
Together with its partners Artelia, Autoroutes Paris Rhin Rhône and the University of Western Brittany, the SMC laboratory is the winner of the call for projects "Ponts Connectés" led by CEREMA, thanks to its project CAHPREEX. Based on the use of RFID sensor technology developed at the University of Western Brittany, this project aims at facilitating inspection work on cable stays and prestressing as well as external prestressing ducts, particularly pipe joints, which are sensitive elements of these structures. Due to their low cost, these RFID sensors should reduce inspection costs while maintaining a high level of monitoring of the instrumented elements. In the end, an in-situ experimentation on structures proposed by APRR will be carried out. This final part will conclude this 2-year project.
Civil engineering infrastructures need to be regularly evaluated regarding their structural health condition. Among the elements to monitor, cables are the most sensitive because they are subjected to severe environmental and mechanical stresses. Monitoring of the common parts of civil engineering structures is increasingly mastered, but there are several parts that are not accessible to conventional monitoring techniques, in particular, cable anchorage zones where damage mechanisms can occur and lead to cable failure.
Among the various potential techniques, we are investigating the potential of acousto-ultrasonics to monitor these very specific areas. The Acousto-ultrasonic technique is an active non-destructive method consisting in the emission and reception of an ultrasonic wave that has interacted with the material/structure. It combines an analysis of the signals collected according to the formalism of acoustic emission with an ultrasonic characterization methodology.
Our laboratory manufactures the test specimens, implements the acousto-ultrasonic systems, and analyzes the collected data.
The VIPP beam project (Viaduct with Independent Spans and Prestressed Beams) in Clerval, led by the Autun laboratory and co-financed by ASFA, CEREMA, and IFSTTAR aims to study the failures of this type of structure, and to verify the capabilities of a repair/reinforcement method increasingly used in this context, namely composite materials bonding.
VIPP-type constructions represent a widely used category of structures in the French heritage, especially in the highway domain. These structures were extensively used between 1955 and 1970 and suffer from many pathologies due to design issues (lack of metallic reinforcement due to the lack of knowledge of some mechanical phenomena); construction issues (absence or poor sealing of the structure, injection defects of the prestressing ducts); as well as material selection issues (steels susceptible to cracking corrosion under tension). Moreover, the increasing traffic evolution confronts these structures with an additional problem not taken into account during their construction, and reinforcement solutions must be implemented.
For the highway managers, these needs imply:
- having non-destructive methods and precise inspection protocols for these structures to best re-evaluate their performance and establish a diagnosis of repair and/or reinforcement needs,
- having adapted and effective repair or reinforcement methods.
In the context of this project, we will focus on studying the use of bonded composite materials, which is now relatively common. While many studies have proven their effectiveness, questions remain, particularly regarding the reinforcement of a damaged prestressed structure.
By working on a real VIPP beam from a structure built between 1952 and 1954, the objective of the Clerval research project was to provide solutions to these two issues. Several control methods have been implemented to evaluate the initial condition of the structure, and different testing phases (bending and then shear) were planned to test the results of these evaluations before and after reinforcement with bonded composites. Finally, the conclusions from these experiments were also be compared to the results that can be obtained using current calculation methods before and after reinforcement.
The SMC laboratory intervened by implementing acoustic monitoring (CASC 2 system) during the testing phases on the entire beam to detect and locate prestressing wire breaks, and acoustic emission during all testing phases on pre-defined local zones of interest to monitor concrete cracking.