Contactless Deformation Monitoring of Bridges with Spatio-Temporal Resolution: Profile Scanning and Microwave Interferometry

Against the background of an aging infrastructure, the condition assessment process of existing bridges is becoming an ever more challenging task for structural engineers. Short-term measurements and structural monitoring are valuable tools that can lead to a more accurate assessment of the remaining service life of structures. In this context, contactless sensors have great potential, as a wide range of applications can already be covered with relatively little effort and without having to interrupt traffic. In particular, profile scanning and microwave interferometry, have become increasingly important in the research field of bridge measurement and monitoring in recent years. In contrast to other contactless displacement sensors, both technologies enable a spatially distributed detection of absolute structural displacements. In addition, their high sampling rate enables the detection of the dynamic structural behaviour. This paper analyses the two sensor types in detail and discusses their advantages and disadvantages for the deformation monitoring of bridges. It focuses on a conceptual comparison between the two technologies and then discusses the main challenges related to their application in real-world structures in operation, highlighting the respective limitations of both sensors. The findings are illustrated with measurement results at a railway bridge in operation

Überwachung von Tragwerken mit Profilscannern

Die Überwachung der Tragwerke von Ingenieurbauwerken ist ein wichtiger Grundstein zur Gewährleistung einer sicheren technischen Infrastruktur. Aufgrund der alternden Infrastruktur und der vielfach gesteigerten Belastung nimmt dabei sowohl die Anzahl an zu überwachenden Ingenieurbauwerken als auch der Umfang der jeweiligen Überwachungsaufgaben zu. Um die daraus entstehenden Herausforderungen zu bewältigen, ergibt sich der Bedarf nach einer effizienten Erfassung von Deformationen unter dynamischer Belastung. Das Ziel dieser Arbeit ist die Realisierung eines Monitoringsystems zur Überwachung von Tragwerken auf Basis eines Profilscanners. Die berührungslose Erfassung mit Profilscannern verringert zunächst den Aufwand für Personal und Instrumentierung im Vergleich zu klassischer, für die Überwachung von Tragwerken eingesetzter Sensorik und ermöglicht zusätzlich das Anmessen von nicht zugänglichen Stellen. Durch die Verfügbarkeit von Informationen entlang eines ganzen Tragwerkprofils können darüber hinaus Analysen flexibel an variierende Fragestellungen angepasst werden. Mit einer Messrate von mindestens 50 Hz können typische Tragwerksdeformationen zuverlässig erfasst und ausreichend Datenmaterial zur Charakterisierung der Deformationsprozesse gesammelt werden. Für den Einsatz von Profilscannern zur Überwachung von Tragwerken wurde neben instrumentenspezifischen Adaptionen, wie der Sensorbefestigung, einer Anzielvorrichtung sowie einer autonomen Stromversorgung, ein universell einsetzbares Prozessierungs- und Auswertekonzept entwickelt. Diese sogenannte raumzeitliche Prozessierung kann durch den Einsatz der diskreten Wavelet- Transformation nahezu vollständig automatisiert werden. Dadurch wird die Analyse der Messreihen in der Orts-Frequenz- bzw. Zeit-Frequenz-Ebene ermöglicht und so die Lokalisierung und Charakterisierung von Unstetigkeitsstellen durchgeführt. Die zentralen Bestandteile der raumzeitlichen Prozessierung sind dabei: • die automatische Korrektur von Fehlmessungen, • die strukturorientierte Segmentierung und Approximation der Messprofile, • die Unsicherheitsbestimmung in Zeitreihen. Obwohl das Messrauschen eines Profilscanners im Vergleich zu traditionell für die Überwachung von Tragwerken eingesetzter Sensorik, wie z. B. induktiven Wegaufnehmern, um ein Vielfaches höher ist, gelingt durch den Einsatz der raumzeitlichen Prozessierung die Ableitung nahezu vergleichbarer Ergebnisse für die Deformationssignale. Insgesamt gesehen wird somit ein automatisierter und effizienter Auswerteprozess realisiert, der durch den Einsatz der diskreten Wavelet-Transformation Ausreißer erkennen und eliminieren bzw. kompensieren kann. Neben der Ergebnisableitung ist so auch eine Qualitätsbewertung unter umfassender Einbeziehung der redundanten Informationen als in situ Unsicherheitsbestimmung möglich. Durch den Einsatz der raumzeitlichen Prozessierung wird an verschiedenen Beispielen das gesamte Anwendungsspektrum von Profilscannern für die Überwachung von Tragwerken gezeigt. Diese reichen von Eisenbahnbrücken bis hin zu Windenergieanlagen und decken den typischerweise bei Tragwerken auftretenden Frequenzbereich bis 10 Hz ab. Durch die nahezu kontinuierliche Erfassung der Tragwerksoberfläche können direkt Deformationsprofile entlang der Tragwerksstruktur abgeleitet werden. Damit wird u. a. die Aufdeckung von Unstetigkeitsstellen der Tragwerksstruktur, wie Risse oder Brüche sowie die Reduktion der Abhängigkeit von Vorwissen für die Messplanung ermöglicht

Development and Performance Verification of the GANDALF High-Resolution Transient Recorder System

With present-day detectors in high energy physics one often faces fast analog pulses of a few nanoseconds length which cover large dynamic ranges. In many experiments both amplitude and timing information have to be measured with high accuracy. Additionally, the data rate per readout channel can reach several MHz, which leads to high demands on the separation of pile-up pulses. For an upgrade of the COMPASS experiment at CERN we have designed the GANDALF transient recorder with a resolution of 12bit@1GS/s and an analog bandwidth of 500\:MHz. Signals are digitized with high precision and processed by fast algorithms to extract pulse arrival times and amplitudes in real-time and to generate trigger signals for the experiment. With up to 16 analog channels, deep memories and a high data rate interface, this 6U-VME64x/VXS module is not only a dead-time free digitization unit but also has huge numerical capabilities provided by the implementation of a Virtex5-SXT FPGA. Fast algorithms implemented in the FPGA may be used to disentangle possible pile-up pulses and determine timing information from sampled pulse shapes with a time resolution better than 50 ps.Comment: 5 pages, 9 figure

Power sector effects of alternative options for electrifying heavy-duty vehicles: go electric, and charge smartly

In the passenger car segment, battery-electric vehicles (BEV) have emerged as the most promising option to decarbonize transportation. For heavy-duty vehicles (HDV), the technology space still appears to be more open. Aside from BEV, electric road systems (ERS) for dynamic power transfer are discussed, as well as indirect electrification with trucks that use hydrogen fuel cells or e-fuels. Here we investigate the power sector implications of these alternative options. We apply an open-source capacity expansion model to future scenarios of Germany with high renewable energy shares, drawing on detailed route-based truck traffic data. Results show that power sector costs are lowest for flexibly charged BEV that also carry out vehicle-to-grid operations, and highest for HDV using e-fuels. If BEV and ERS-BEV are not charged in an optimized way, power sector costs increase, but are still substantially lower than in scenarios with hydrogen or e-fuels. This is a consequence of the relatively poor energy efficiency of indirect HDV electrification, which outweighs its temporal flexibility benefits. We further find a higher use of solar PV for BEV and ERS-BEV, and a higher use of wind power and, to some extent, fossil generators for hydrogen and e-fuels

Geochemical Changes Associated with High-Temperature Heat Storage at Intermediate Depth: Thermodynamic Equilibrium Models for the DeepStor Site in the Upper Rhine Graben, Germany

The campus of the Karlsruhe Institute of Technology (KIT) contains several waste heat streams. In an effort to reduce greenhouse gas emissions by optimizing thermal power consumption on the campus, researchers at the KIT are proposing a ‘DeepStor’ project, which will sequester waste heat from these streams in an underground reservoir during the summer months, when the heat is not required. The stored heat will then be reproduced in the winter, when the campus’s thermal power demand is much higher. This paper contains a preliminary geochemical risk assessment for the operation of this subsurface, seasonal geothermal energy storage system. We used equilibrium thermodynamics to determine the potential phases and extent of mineral scale formation in the plant’s surface infrastructure, and to identify possible precipitation, dissolution, and ion exchange reactions that may lead to formation damage in the reservoir. The reservoir in question is the Meletta Beds of the Upper Rhein Graben’s Froidefontaine Formation. We modeled scale- and formation damage-causing reactions during six months of injecting 140 °C fluid into the reservoir during the summer thermal storage season and six months of injecting 80 °C fluid during the winter thermal consumption season. Overall, we ran the models for 5 years. Anhydrite and calcite are expected mineral scales during the thermal storage season (summer). Quartz is the predicted scale-forming mineral during the thermal consumption period (winter). Within ~20 m of the wellbores, magnesium and iron are leached from biotite; calcium and magnesium are leached from dolomite; and sodium, aluminum, and silica are leached from albite. These reactions lead to a net increase in both porosity and permeability in the wellbore adjacent region. At a distance of ~20–75 m from the wellbores, the leached ions recombine with the reservoir rocks to form a variety of clays, i.e., saponite, minnesotaite, and daphnite. These alteration products lead to a net loss in porosity and permeability in this zone. After each thermal storage and production cycle, the reservoir shows a net retention of heat, suggesting that the operation of the proposed DeepStor project could successfully store heat, if the geochemical risks described in this paper can managed

VESTA - Very-High-Temperature Heat Aquifer Storage

Energy storage is one of the key challenges of the energy transition. Eight international partners from Germany, Switzerland and the USA address this challenge in the joint project VESTA. Goal of VESTA is the generic development and demonstration of high-temperature storage in the underground. Four pilot sites in the DACH region in various geologies and project phases allow feedback loops between generic scientific investigations and application of new geothermal technologies. Specifically, pilot sites that shall 1) demonstrate HT-ATES technology, 2) evaluate technical and non-technical barriers, 3) support development and implementation by providing techniques and optimized component design, and 4) support agencies with scientific and technical knowledge as a basis for advancing regulatory provisions. With this scientific program, VESTA shall form a technical-economic bases for future operational concepts