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Eingeladener Vortrag
- nein (56)
Periodic mapping of reinforcement corrosion in intrusive chloride contaminated concrete with GPR
(2014)
This paper presents an experimental effort for developing a novel reinforcement corrosion monitoring technique based on Ground Penetrating Radar (GPR). Experiments were carried out to periodically monitor the accelerated reinforcement corrosion process with GPR. The data were processed in both time and timefrequency domains to investigate the tendencies of GPR signal attribute changes related with corrosion, moisture and chloride contamination. Data processing methods were proposed to visualize the reinforcement corrosion and chloride distribution with target specified signal attribute mapping. Half-Cell Potential (HCP) and Laser-Induced Breakdown Spectroscopy (LIBS) methods were employed to verify the GPR observations.
Für den Entwurf neuer Bauwerke gewährleistet die Einhaltung aktuell gültiger Normenwerke eine ausreichende Sicherheit. Diese Normen und die zugehörigen Lieferbedingungen gelten ausschließlich für Neubauten aus heute produzierten Stählen. Technische Regeln für die Begutachtung alter Materialien, wie sie zuletzt im Beiblatt 2-"Altstahl im Hochbau" von 1948 zur DIN 1050 "Stahl im Hochbau" [35] verankert waren, sind zurückgezogen worden. Bei der Bewertung alter Baukonstruktionen greift man häufig auf vorhandene Materialinformationen aus Bauwerksunterlagen, Vorschriften und Berechnungen, z.B. im Verantwortungsbereich der Deutschen Bahn AG, zurück. Die geltende Richtlinie der Modulfamilie 805.001 der Deutschen Bahn AG [21] erlaubt in Abschnitt 2, Absatz (2) sogar ausdrücklich die Nutzung alter Berechnungen und Vorschriften, wenn bei gleich bleibender Nutzung nur Eingriffe von untergeordneter Bedeutung, wie kleine Reparaturen oder lokale Verstärkungen, vorgenommen werden. Ein Eingriff in die Tragsicherheit des Bauwerkes ist nicht zulässig. Für umfassendere Maßnahmen und für Bauwerke außerhalb des Zuständigkeitsbereiches der Deutschen Bahn AG oder für die Bewertung der Konstruktionen bei Umnutzung bzw. bei umfangreichen Maßnahmen ist diese Ausnahme nicht anwendbar. Daraus ergibt sich für den auf die Beurteilung und Bewertung von bestehenden Bauwerken spezialisierten Ingenieur der Bedarf, alte Materialien, Bauweisen und Vorschriften zu kennen und zu verstehen. Aufwändige Versuchsserien an originalen Vollwand- und Fachwerkträgern zur Ermittlung von Schadensmechanismen im einstufigen Ermüdungsversuch werden vorgestellt. Sie resultieren in erweiterten Kenntnissen über Versagenskriterien für genietete Bauteile. Die Weiterentwicklung und Erprobung einander ergänzender zerstörungsfreier und minimal-invasiver (zerstörungsarmer) Verfahren verbessert die Schadensfrüherkennung an ermüdungsbeanspruchten Stahlkonstruktionen, z.B. bei Inspektionen. Intensive Materialuntersuchungen zur Mikrostruktur und zu mechanischen Materialparametern tragen zum Verständnis bestimmter, für moderne Stähle untypischer, Schadensmechanismen bei. Die interdisziplinäre Kooperation mit den Laboratorien der Abteilungen V, VIII und S bei der Analyse von Rissentstehung und Risswachstum erweitert die verfügbaren Kenntnisse über das Versagensverhalten alter Stähle und Stahlverbindungen. Aufbauend auf einer Darstellung der Entwicklung alter Bauweisen und Bauwerke, einer Literatur- und Normenanalyse zu Lieferbedingungen von Stahl für das Bauwesen und zu konstruktiven Details, so wie sie um die Jahrhundertwende zwischen dem 19. und 20. Jh. üblich waren, werden Materialuntersuchungen an alten Stählen, Ermüdungsversuche und Messungen an bestehenden Brückenbauwerken aus alten Stählen präsentiert. Innerhalb des Projektes gab es eine enge Zusammenarbeit mit Brückenbetreibern, die gewährleistete, dass die Ergebnisse aus Prüfungen, Forschung und Entwicklung direkt in die Praxis, aber auch in interne Vorschriften der Brückeneigner überführt werden konnten. So wurde in der Subgroup Remaining Fatigue Life of Bridge Structures der Gruppe ECOBRIDGE der Europäischen Eisenbahn Vereinigung UIC unter Beteiligung der BAM eine Machbarkeitsstudie [1] zusammengestellt. Auf dieser Basis erarbeitete ein bilaterales Konsortium der Schweiz und Deutschlands im Auftrag der Schweizerischen Bundesbahn und der Deutschen Bahn mit Ermüdungsspezialisten der RWTH Aachen, der EPFL Lausanne und der BAM einen Vereinheitlichten Sicherheitsnachweis für die Beurteilung alter Eisenbahnbrücken aus Stahl [2]. Der Abschlussbericht liegt seit 2001 im federführenden Institut für Stahlbau der RWTH Aachen vor. Die Überführung der Forschungsergebnisse in eine Richtlinie der Europäischen Konvention für Stahlbau (EKS) mit empfehlendem Charakter liegt als Entwurf [4] vor. Die Veröffentlichung nach abschließender Begutachtung durch namhafte auf Altstahl und Ermüdung spezialisierte Fachkollegen durch die EKS ist in Vorbereitung.
Dokumentation von Ermüdungsversuchen an genieteten Querträgern einer schweißeisernen Trogbrücke
(2001)
Ermüdungsversuche an alten genieteten Stahlbrücken: Beurteilung der verbleibenden Restnutzungsdauer von Querträgern einer originalen schweißeisernen Trogbrücke nach fast einhundert jähriger Nutzung. Verbindungen und Elemente des alten Bauwerks sind zunächst unter Verkehr und nach dem Abriss der Brücke im Labor getestet worden. Es kamen sowohl Dehnungsmessungen als auch zerstörungsarme bzw. Zerstörungsfreie Prüfverfahren zur Anwendung. Materialuntersuchungen, auch neuartige, wie z. B. Rissfortschrittversuche, Gefügeuntersuchungen und Zugversuche ergänzten die Untersuchungen.
Laboratory model test for monitoring the new main railway station of Berlin - The Lehrter Bahnhof
(2002)
Inspection of steel bridges
(2007)
Assessment of existing steel structures - A guideline for estimation of the remaining fatigue life
(2007)
In many countries and regions, traffic infrastructure projects suffer from low funding. The budget is tight for new infrastructure building and, thus, the importance of inspection, maintenance and assessment of the existing traffic infrastructure increases. A new fatigue assessment guideline for the estimation of the remaining fatigue life of steel bridges has been written by technical committee 6 of the European Convention of Constructional Steelwork (ECCS). It will be a useful tool for the complementation of bridge management systems, used commonly for condition assessment.
Design specifications and rules are harmonised throughout Europe. They are under constant development, but there is still a lack of forwarding and concentrating experiences as well as developing rules for the fatigue assessment on existing steel structures. This paper presents a guideline with a proposed fatigue assessment procedure for existing steel structures embedded in information about old materials and non-destructive testing methods for the evaluation of details (ECCS 2004, Assessment of existing steel structures). Particular attention is paid on remedial measures which are proposed for weak details and damages caused by fatigue. The developed fatigue assessment procedure can be applied to existing steel structures under cyclic loading in general, but the guideline concentrates on the existing traffic infrastructure made from old steel, because of the public importance. The proposed procedure summarizes, regroups and arranges the knowledge in the field of assessment on existing steel to be applied by practicing engineers. The procedure is a milestone in knowledge transfer from a state of scientific knowledge to state-of-the-art.
Assessment of existing steel structures - Recommendations for estimation of remaining fatigue life
(2008)
Acoustic measurement methods
(2008)
Concrete railway bridges - taxonomy of degradation mechanisms and damages identified by NDT methods
(2006)
Assessment of existing steel structures - A guideline for estimation of the remaining fatigue life
(2007)
Die zunehmende Bedeutung der Nachhaltigkeit im Bauwesen wird in Zukunft das Bauen im Bestand gegenüber Neubauten in den Vordergrund rücken. Dies gilt auch für den Brückenbau, wo das Qualitätsmanagement seit langem Brücken von ihrem Entstehungsgang über den Betrieb bis in die Entsorgung begleitet.
Die starke Vergrößerung der Frachtvolumina für Straße und Schiene und die zunehmende Überalterung des Brückenbestandes fragen danach, ob die bestehenden Brücken für die veränderten Betriebsbedingungen noch geeignet sind und wie sie und ob sie dafür instandgesetzt werden könnten.
Für die erforderlichen Instandhaltungs- und Instandsetzungsmaßnahmen oder einen eventuellen Ersatz durch einen Neubau ist aber die Frage der Restnutzungsdauer von entscheidender Bedeutung. Es ist daher nicht von ungefähr, dass sich Baulast-träger auf nationaler und internationaler Ebene frühzeitig zusammengetan haben, um nach geeigneten Methoden der Bestimmung der Sicherheit und Restnutzungsdauer bestehender Brücken zu forschen. Auch die internationalen technisch-wissenschaftlichen Verbände wie EKS und fib sowie die Standard-Organisationen ISO und CEN sind der Frage eines internationalen Austauschs und der Vereinheitlichung der Methoden nachgegangen.
Für Stahlbrücken hat insbesondere das technische Komitee6 - Ermüdung - der EKS Anregungen aufgegriffen, aus den verschiedenen nationalen Erfahrungen und dem vorhandenen Wissen technische Empfehlungen für die Beurteilung bestehender Stahlbrücken zu entwickeln [1], die sich als Grundlage für die von CEN/TC 250 - das CEN-Komitee für die Bearbeitung der Eurocode - geplante Erweiterung der Eurocode zur Instandhaltung und Instandsetzung des Brückenbestandes eignen.
Das Ergebnis ist ein technisch-wissenschaftlicher Bericht, der im Rahmen der Zusammenarbeit der europäischen Kommission (DG-Research - Joint Research Centre JRC) mit der EKS als Basispapier für eine zukünftige Eurocode-Erweiterung veröffentlicht wurde und schon jetzt als Empfehlung für eine Vorgehensweise nach dem Stand der Technik verwendet werden kann.
Der vorliegende Beitrag behandelt die Grundzüge dieses Berichtes [1], der vom e-bookshop der Kommission kostenfrei herunter geladen werden kann.
In this research, laboratory experiments were carried out to investigate the feasibility of using ground penetrating radar (GPR) for corrosion detection and/or monitoring, and the mechanism of corrosion caused GPR signal changes, taking into account the influence of several parameters: Chloride, rebar size and cover depth. With the understanding of the mechanism, a novel method for detecting reinforcement corrosion in concrete with GPR is proposed, together with a series of signal processing toolkits for corrosion visualization and image comparison.
Ultrasound sensors should be embedded into concrete for monitoring concrete properties. These new longitudinal wave sensors with a center frequency of 60 kHz were examined regarding their suitability for ultrasonic measurements in concrete structures in terms of emission characteristics, sensitivity and frequency ränge.
For the measurement of the radiation patterns, the sensors were embedded vertically and horizontally in concrete cylinders. The directivity pattern was measured using a laser vibrometer.
The sensitivity of the sensor was determined in water using different sensors of the same type. It shows changes in the signal amplitude as well as variations in the frequency ränge for different transmitter-receiver combinations.
The attenuation of the concrete affects the achievable resolution of the measurements and thus, the maximum possible spacing of the sensors within a concrete element. Experimental tests helped optimizing the distances with respect to the required resolution and the effort of embedding the sensors. The signal attenuation in the concrete was measured in the frequency ränge of 60 kHz in response to various degrees of reinforcement and grain size. For this purpose, the sensors were cast at different distances in the specimens studied. The recorded Signals were evaluated for their amplitude and frequency spectrum.
Measurements, NDT and laboratory testing of the wrought iron bridge at Berlin-Friedrichstraße
(2010)
Messungen und Laborversuche an der schweißeisernen Spreebrücke an der Berliner Friedrichstraße
(2010)
Monitoring accelerated corrosion in chloride contaminated concrete with ground penetrating radar
(2012)
Condition assessment of old railway bridges, a scientific cooperation between Berlin and Wroclaw
(2009)
Two years ago, the East Prussian and the Low-Silesian Railway lines celebrated their 160th anniversaries. The history of both first railway connections in the Eastern railway network development in the whole region in the 19th century is presented together with information about the railway between Berlin and Wroclaw. Special attention is paid to the railway bridges built in this period. The first large iron bridges and typical masonry arch structures are presented. Special attention is paid to masonry arches. The condition appraisal of existing masonry arches requires new developed technical methodologies, effective tools and procedures for the description of the bridges current state and function. Their current technical condition as well as service-ability is described.
The European infrastructure asset has developed historically and is characterized by nation-specific construction processes. Inspection, condition assessment, and maintenance procedures differ from country to country. Because of historical and political circumstances, national infrastructure assets are maintained at different levels, too. Since the budget for maintaining the bridge infrastructure less and less meets the demands of a growing bridge stock, bridge inspection, maintenance, and life-cycle considerations gain higher importance. The need exists to develop effective diagnosis tools for early detection of construction faults, defects, and deterioration processes during inspection, to keep the bridge infrastructure at an acceptable level, from structural safety and economic viewpoints. An overview on the latest research projects and integrated bridge management systems in Europe is given. The potentials of nondestructive testing (NDT) are presented, with special focus on technical advances of NDT applications to reinforced concrete (RC) and posttensioned concrete bridges. Although NDT is not regularly integrated in these processes, the application brings valuable information on the current condition of the inner structure in called-in special inspections. NDT-automation and the application of imaging echo methods, combined with advanced data processing, produce a surprising level of information about the inner structure of massive RC slabs up to a depth of about 60 cm. Detected inhomogeneity and scatterers of acoustic or electromagnetic waves can be visualized in vertical or horizontal slices through the structure or animations. The fusion of different three-dimensional data sets of processed data improves the interpretability and accuracy of the results.
Complex special inspection of an old masonry arch bridge according to the Guideline on Inspection and Condition Assessment of Railway Bridges and numerical analysis of the structure are presented. The guideline summarises recommendations for the step-by-step investigation of railway bridges applying enhanced methods developed during the EU-funded project Sustainable Bridges. For the investigation of the arch barrel, the ballast parameters and the inner structure of the backfill behind the arch barrel a number of various advanced non-destructive and minor-destructive testing methods were applied. Deformation of the structure during load tests was measured using three independent measuring systems: laser vibrometer, LVDT and microwave radar. Results of calculations performed with 2D and 3D models based on FEM are compared with the field load tests. Sensitivity of the ultimate load of the structure to investigated parameters is studied in FE model. Some general conclusions according to methods of testing and modelling of masonry arch bridges are presented and discussed.
Complex special inspection of an old masonry arch bridge according to the Guideline on Inspection and Condition Assessment of Railway Bridges and numerical analysis of the structure are presented. The guideline summarises recommendations for the step-by-step investigation of railway bridges applying enhanced methods developed during the EU-funded project Sustainable Bridges. For the investigation of the arch barrel, the ballast parameters and the inner structure of the backfill behind the arch barrel a number of various advanced non-destructive and minor-destructive testing methods were applied. Deformation of the structure during load tests was measured using three independent measuring systems: laser vibrometer, LVDT and microwave radar. Results of calculations performed with 2D and 3D models based on FEM are compared with the field load tests. Sensitivity of the ultimate load of the structure to investigated parameters is studied in FE model. Some general conclusions according to methods of testing and modelling of masonry arch bridges are presented and discussed.
A toolbox with non-destructive testing methods for the condition assessment of railway bridges
(2006)
The unified economic structure of the European market requires a unified transport infrastructure to ensure seamless and barrierfree transportation of passengers and goods. The European commission is funding the European Integrated Project Sustainable Bridges to comply with future traffic demands. The main objective of the project is to reliably assess and upgrade the bridge infrastructure for the required increase of axle loads and transport volume. 32 Institutes from 12 countries develop unified procedures for the assessment and improvement of the existing railway bridge stock under the guidance and review of six major European railway companies.
Non destructive testing (NDT) is given a high priority. One of the work packages concentrates on the potential of advanced NDT-methods and creates a toolbox with advisable methods for the condition assessment of all types of railway bridges. Although NDT-methods are implemented in the quality assurance process in many industries, their application in the railway infrastructure is not common. Only a few countries have included selected NDT-methods into advanced condition assessment procedures for the management of their bridge stock.
This paper describes also current activities to enhance pulse-phase thermography, impulse-radar and acoustic methods. The advanced methods enable infrastructure owners to verify construction plans, to assess structures, repair and strengthening quality or to identify in-service damages. Latest development is an automated scanning system for combined acoustic and electromagnetic measurements. The results are then combined through data fusion techniques to further increase their value for the bridge owners.
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.
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.
The Berlin Main Station was built between 2000 and 2006. At the occasion of the 10th anniversary after the Berlin Main Station was officially opened to train traffic, a view back on eight years of monitoring was given. For the period of the construction with different load cases, the monitoring system was required by the Railway Authorities (Eisenbahnbundesam, EBA) to survey differential vertical displacements between neighbouring supports of the glas roof and the partially prestressed middle bridges. 128 sensors were installed.The data was published in the Internet with access restricted to the BAM scientists and the owner of the station, the German Railways DB AG.
Civil engineers, who are involved in nondestructive testing have to solve an essential task: the transfer of the results of NDT-research into practice. NDT in civil Engineering is a quite new discipline. The results must meet the needs of the infrastructure owners to convince them about the usefulness of NDT. The issue of reliability of the NDT-data was discussed.
The research project "Ultrasonic Net for Concrete Monitoring (UNeCOM)" aims at developing a methodology for an embedded ultrasonic network for the condition assessment of infrastructure constructions. Civil engineering structures made of concrete, which are located in tectonically active regions or undergo special loading conditions, may require continuous monitoring. It is important to assess the condition of the building and its stability to recognise and classify the effect of a seismic event or evolving damage at early stages before failure occurs. Embedded ultrasonic sensors offer the possibility to detect changes in the material and degradation mechanisms from inside the structure in areas which are difficult or impossible to inspect otherwise. In contrast to conventional ultrasonic testing methods, where the concrete surfaces are scanned with ultrasound probes, this new approach uses sensors, which are embedded into concrete, eliminating the effect of variable coupling conditions between sensors and concrete. This method allows an integral detection of changes in the concrete structure, for example due to seismic activities, to detect mechanical impacts, as well as degradation of the material due to overloading. Such methods have great relevance especially for the monitoring of constructions like power plants, bridges, offshore structures and other structures with high technical safety requirements. The sensor network can be controlled remotely through the internet which is also being used for data transfer. The embedded sensor network is designed to monitor structural damage and concrete degradation globally with high sensitivity.
The Berlin Congress Hall was a gift of the United States of America to Germany for the Berlin World Exhibition in 1957. The elegantly double-curved roof was made from an advanced prestressed concrete construction. The construction followed the design by the American architect Hugh Stubbins with special structural modifications to comply with German construction rules. No early indications for failure initiation were detected before a sudden partial collapse. On May 21st, 1980, the Southern external roof overhang collapsed. In December 1980, Jörg Schlaich and his co-authors published a summarizing expert opinion about structural causes of failure. The present paper mainly introduces results of cause analysis made at the Federal Institute for Materials Research and Testing (BAM), mandated by the Public Prosecutor at the Berlin District Court to specify the causes of the sudden failure. This paper refers to BAM-publications about analyses that were performed under this mandate and published – most of them in German language – within the first years after failure. The expert's opinions comprise structural considerations materials investigations, metallographic analyses and corrosion. Nowadays experts have learnt from the failure and built a slightly modified roof in the original shape at the 750th birthday of the city of Berlin and re-opened the former Berlin Congress Hall to the public on May 9th, 1987. The Hall is now serving as the House of the Cultures of the World, following the initial intention of the hall.
Adolf Martens (18501914) was a pioneer of materials engineering. After his studies in Berlin he joined a railway company being responsible for the technical equipment. His interest for the basic mechanisms of mechanical strength and fracture of metallic materials led him to the development of the basic concepts for metallography; his papers published between 1878 and 1889 laid the fundament of this technique. In 1880 Martens changed to the Royal Industrial Academy in Berlin and by 1884 he was designated as director of the Materials Testing Laboratory at the Technical University Berlin. Under his guidance this institution acquired an excellent reputation in all relevant areas of the German industry, forming the nucleus of the Bundesanstalt für Materialforschung und -prüfung (BAM) – the Federal Institute for Materials Research and Testing. Martens developed equipment in many different areas as mechanical testing of metallic materials and of paper, characterization of the wear behavior of materials and viscosity of lubricants. His overwhelming contribution to materials engineering was recognized as early as 1895 by Floris Osmond, who denominated martensite a metallographical constituent resulting from quenching of steels. In 2000 ISO designated the value obtained from the instrumented indentation method as Martens Hardness – HM.