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Eingeladener Vortrag
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Cast iron arch bridges were built in the late 18th and early 19th century across Europe. After the famous Iron Bridge in the Ironbridge Gorge in Coalbrookdale in England, being now part of the UNESCO world heritage, many cast iron bridges followed and substituted timber bridges. A series of cast iron bridges has been built in central Europe, in Laasan, Breslau, (now Wrocław), in Berlin, Potsdam, Bad Muskau and Schwerin. The paper gives an overview about the current state of some remaining cast iron arch bridges, typical damage cases, material properties and rehabilitation. Most of the old cast iron arch bridges serve as pedestrian bridges. Some of these bridges have been strengthened to increase the traffic load. Different rehabilitation measures as substitution of parts of the bridges and strengthening using Carbon Reinforced Polymers (CFRP) are discussed.
The presented development of a damping model is a research component of an experimental feasibility study about moisture in building materials measured with Bluetooth® Low Energy (BLE) signals. This study may be part of a structural health monitoring aiming on early damage detection in the built infrastructure and is increasingly focusing on wireless sensor Network technology. It is investigated, how the Received Signal Strength Indicator (RSSI) of a BLE signal, transmitted from the BLE-module embedded in building materials with changing moisture content is damped. The BLE-module communicates with a mobile Smart Device as tablet or mobile phone via 2.45 GHz-ISMfrequency band where water dipoles start to oscillate. If the BLE-signal transfers through a moist material, the moisture Content influences the RSS-Indicator. The damping model demonstrates this damping effect on RSSI by the abstraction of the reality observed in a real system.
Nuclear Power Plants have been in operation for ca. 50 years. Based on this experience, non-destructive testing tasks specific to thick and highly reinforced nuclear containment structures have materialized. The performance based Service life extension of existing NPPs also needs a measurement based decision to support continuing the service of the concrete part of the installations.
By nature, concrete is a very durable material and any natural Deterioration processes may take a long time to become critical to the structure. The experience of more than 50 years of service limits the testing tasks to a few ones which are not yet solved.
Research in NDT of concrete structures is performed by many research institutions all over the world with different technical and systematic approaches. Results are mainly obtained on laboratory specimens, sometimes additional field studies are reported. This research takes place independently without coordination and as a result, the outcomes mostly lack full comparability.
Software for data analysis has become indispensable and very powerful. This part of testing needs more attention when it comes to evaluate test results. Validation of NDE solutions is becoming a critical part in concrete structure testing.
Validation is by definition the proof that a customer´s requirements in the test are being met by the testing solution. This includes equipment, personnel qualification and data analysis. In the following tables, the research recommendation Validation is used in the sense, that proof of the performance of existing solutions needs to be adressed. In general, a validation methodology for NDE solutions for concrete testing in itself needs to be researched and established.
Comparability of research also needs an accepted and easily accessible reference. From experience, it is almost impossible to manufacture exact copies of test specimens at different locations. Round Robin tests are therefore needed to evaluate the performance of a test.
Data evaluation is generally done using dedicated software, sometimes Hardware dependant and not interchangeable between systems. Software is ever more increasingly becoming more powerful and sophisticated. An in-depth evaluation needs to address the comparability and validation of Software used for data analysis and evaluation. The vision of a unified software pool for NDE investigations would undoubtedly support research tremendously.
Quantitative NDE is mostly recommended to assess the condition of a structure. However, qualitative data can be very useful, especially for processes which change the material properties or deteriorate the structure (e.g. corrosion of reinforcement). The need for reliable baseline data is a key factor for such monitoring tasks.
Active thermography
(2017)
Active thermography is introduced as tool for diagnostics in civil engineering structures. Aside from basic information, examples for applications of active thermography in different types of structures was presented. Active thermography was applied in historic structures to reveal former components or even ancient openings. Other examples present active thermography as a tool for nondestructive detection of debonding in CFRP strengthened structures. The way is explained, how the system was optimized for different materials.
Practical applications of recent BAM-research results of NDT and monitoring in civil engineering
(2018)
Nondestructive testing and monitoring was of mayor interest in BAM-research related to the survey of civil engineering structures during the last two decades. Three case studies about research projects carried out at BAM were presented. All three projects focussed on the survey of parameters and safety related tasks in bridge engineering and inspection. First, the monitoring of the Berlin main station was presented with focus on the sensors developed specifically for this project. The second case study presented and application of guided ultrasonic waves to CFRP-strengthened bridges. The method was sucsessully applied to two of four different strengthening measures carried out min. 10 years ago. The last project presented the feasibility study of a network consisting of simple Bluetooth modules to survey changes in the moisture content in sand and massive concrete.
Within the presented research project, experimental and numerical investigations were performed to develop a thin-shelled, modular, mobile element system made of a micro-reinforced ultra-high-performance ductile concrete (DUCON®). Material parameters were experimentally determined to adapt the material model within the numerical analysis applying the Drucker-Prager relationship. Afterwards, for validation of the numerical models, quasi-static and high-velocity impact tests were performed on plate-like structures. Finally, a suitable geometry of transportable barrier elements will be designed, which provides a maximum of resistance against impact by a minimum of weight and a maximum of mobility.
The presented development of a damping model is a research component of an experimental feasibility study about moisture in building materials measured with Bluetooth® Low Energy (BLE) signals. This study may be part of a structural health- and long-term monitoring aiming at early damage detection in the built infrastructure and is increasingly focusing on wireless sensor network technology. It is investigated, how the Received Signal Strength Indicator (RSSI) of a BLE signal, transmitted from the BLE-module embedded in building materials with changing moisture content is damped. The aim of the modelling is the derivation of a damping equation for the formal model to determine the moisture damping exponent to finding a correlation.
The book chapter first analyses the history of higher education in Europe. Second step describes the current Bologna process. Finally, the rule of the Bundesanstalt für Materialforschung und -Prüfung (BAM) in supporting PhD-students during their research and preparation of theire theses in cooperation with Universities is described
Current measurement methods for dertermination of moisture analyse near-surface moisture distribution. During an externally funded research project, microwaves in the Bluetooth(R) frequency band width were utilized for Setting-up a module network. Without additional sensors, the feasibility study confirmed that threedimensional data can collected to obtain a threedimensional data set as basis for the estimation of moisture distribution inside massive building materials.