Bridges are an important element of the road network and are therefore very significant for researching the safety of structures. How do different forces and oscillations affect the individual parts of a bridge? At what speed do cracks in the concrete wall increase? The answers to these questions help determine the need for repair and forecast aging processes. This in turn helps to prevent future damage and reduce repair costs.
Promoting young scientists and networking knowledge in the safety of structures field also plays a decisive role in the advance of scientific knowledge and procedures. The European Union funds various exchanges between young scientists as part of the Horizon 2020 programme. Around 3.2 million euros are available for the INFRASTAR project. INFRASTAR supports the research work of twelve Ph.D. students from five countries. They participate in multidisciplinary, intersectoral – meaning private and public sector – training. The project enables Ph.D. students to share and expand their widespread knowledge on the maintenance management of the built infrastructure. Lijia Long, Ph.D. student in the Safety of Structures Department, and Xin Wang, Ph.D. student in the Non-Destructive Damage Assessment and Environmental Measurement Methods Division, are part of the INFRASTAR network.
Finding damage in structures using coda waves and tree diagrams
Ultrasound measurements on structures offers the advantage that the ultrasonic sensors used in the concrete continuously monitor the condition of a structure and can detect defects that are not visible from the outside. Ph.D. student Xin Wang is involved in the development of innovative ultrasound networks for structural monitoring at BAM.
Changes between damaged and intact structures shows that damage can sometimes not be detected when mapping the direct ultrasonic wave. However, the wave train following the direct ultrasonic wave is randomly deflected even at a small nonuniformity in the material. This delays its arrival at the measuring points. This wave train, also called the ‘coda wave’, provides appropriate information about the condition of the structure by means of sensitive coda wave interferometry. Xin Wang summarises the advantage of this method: "This method enables the early detection of minor and impending damage in a structure".
Ph.D. student Lijia Long in the Safety of Structures Department is determining the added value of structural monitoring with modern measuring technology. Cost-benefit statements are made about the use of modern measuring technology for damage assessment using probability calculations for different approaches. "The statements serve as a decision-making tool to help select the measuring method that is most suitable and at what point the monitoring and procedures such as a repair of the structure, are particularly useful," says the researcher Long.
Researching more together
INFRASTAR provides helpful impulses for their research work. "The training and research visits to the project partners provide exciting ideas for joint research projects", explains Lijia Long. Research reports are thus often compiled in international, multidisciplinary groups. In order to clearly detect damage, it is also usually necessary to link the measurements of several physical quantities with each other. "Coda wave interferometry captures the moment fractures form in the structure. In contrast, fibre optic sensors can identify the position of these fractures. Combining the methods brings together their significance", says Xin Wang.
Through the visits and training workshops, BAM also contributes to the education of the other Ph.D. students. Dr. Ernst Niederleithinger from the Non-Destructive Damage Assessment and Environmental Measurement Methods Division is the head of the INFRASTAR subproject ‘Monitoring and Auscultation’ and provides training in the field of monitoring and non-destructive testing of structures. The joint research also uses the model ‘reference bridge’ from BAM‘s project BLEIB (German for assessment, service life forecast and repair of bridges) at BAM’s Test Site for Technical Safety (BAM TTS) at Horstwalde. In their blogs, the two Ph.D. students also report on their experiences as trainee researchers and on the INFRASTAR project. Lijia Long does not blog solely to inform, but also to motivate other young people to get involved in science.
The ‘Innovation and Networking for Fatigue and Reliability Analysis of Structures – Training for Assessment of Risk’ project (INFRASTAR) provides innovative, multidisciplinary and intersectoral training for young asset management researchers for the built infrastructure. The emphasis lies on forecasting the behaviour of concrete structures during fatigue. INFRASTAR deals with two representative structure types: bridges and the towers and foundations of wind turbines.
The aim of the project is to train young researchers. It supports twelve Ph.D. students in five countries. INFRASTAR also helps extend the service life of structures, reduce operating costs, and provides risk-based lifespan methods for the design of future structures.
This project is funded by the European Union under the Horizon 2020 programme through the Marie Skłodowska-Curie grant agreement No 676139.Running time: 01/05/2016-30/04/2020