Dietmar Hosser

A framework for reliability-based system assessment based on structural health monitoring

The safety and usability of transport infrastructures is of great importance for the entire society, because disturbances of traffic networks can have significant consequences for the economy and the environment. Especially today, when bad news about deteriorated structures and shortened public budgets are omnipresent, this must not be forgotten. Structural health monitoring (SHM) can help to ensure the safety of deteriorated structures. SHM is expensive and therefore the investigation of optimized inspection and monitoring strategies is an active field of research. The Collaborative Research Centre (CRC) 477 at the Braunschweig University of Technology investigates innovative methods for SHM. In project field A1, a framework for the probabilistic safety assessment of structures has been developed using data from SHM. The current paper describes and explains the methodology of the framework and shows its application using a substitute structure, which was built for the CRC 477.

Evaluation of simplified calculation methods for structural fire design

Abstract Several simplified calculation methods have been developed for structural fire design. Their function is to bridge the gap between element classification according to design tables, which are often too coarse for practical work, and elaborate scientific computer codes, which remain inaccessible for normal users. The aim of this paper is to compare and evaluate existing analytical methods for fire design of structural elements made of reinforced concrete, structural steel or timber. The fundamentals of these methods are outlined and discussed with regard to fire load, thermal and mechanical high-temperature behaviour of the materials, thermal and mechanical analysis of cross-sections and structures, and safety concept. The existing methods are valuated taking into account different criteria, e.g. consistency, theoretical and experimental verification and applicability of the procedure and input data. The overall uncertainties and deviations from existing test results are determined and covered by a global safety margin.

Modelling simplification of landfill processes by using methods of reliability theory.

By the year 2005 most landfills in Germany will be closed down and begin the closing phase and later the after-care phase. So far there have been only a few scientific investigations concerning the hazard potential of stored waste for the environment. For this reason, it is necessary to predict how the hazard potential of landfills will vary after closure. The prediction can be made by describing the coupled processes of biodegradation and pollutant transport using models that are currently being developed. These models deal with highly non-linear differential equations having a large number of parameters. In order to permit application of the model in practice, it is necessary to reduce these to parameters which are essential to the reliability of the landfill. They have to be identified by sensitivity investigations with the aid of methods of reliability theory so that models can be limited to these essential parameters and the calculation effort as well as measurement of parameters (monitoring) can be considerably reduced.

Seismic risk analyses in the German Risk Study, Phase B

Abstract The paper discusses some aspects of the seismic risk part of the German Risk Study for Nuclear Power Plants, Phase B. First simplified analyses in Phase A of the study allowed only a rough classification of structures and systems of the PWR reference plant according to their seismic risk contribution. These studies were extended in Phase B using improved models for the dynamic analyses of buildings, structures and components as well as for the probabilistic analyses of seismic loading, failure probabilities and event trees. The methodology of deriving probabilistic seismic load descriptions is explained and compared with the methods in Phase A of the study and in other studies. Some details of the linear and nonlinear dynamic analyses of structures are reported in order to demonstrate the influence of different assumptions for material behaviour and failure criteria. The probabilistic structural and event tree analyses are discussed with respect to distribution assumptions, acceptable simplifications and model uncertainties. Some results for the PWR reference plant are given.

Reliability-based Design Of Structural Members For Nuclear Power Plants

The reliability of load bearing structural members in NPP has been proved by 1st order reliability theory. Studies on the temperature development in safety related compartmenm and the failure probability of adjacent concrete members were performed. Special effects e.g. due to forced ventilation and fire extinguishing systems are accounted for in the calculations with a post-flashover heat balance model. Simplified failure models describing the load bearing capacity of concrete members were applied to check the reliability of different types of building members. The results indicate that the member temperatures and the life loads are the most important parameters. Therefore the practical design may be performed by using partial factors for the temperatures and reduction factors for the life loads. It turned out that as a rule 90 minutes fire duration acc. to DIN 4102 is a sufficient value for NPP fire compartments.

Brandverhalten von ultrahochfestem Beton

Derzeit bestehen noch erhebliche Kenntnislucken hinsichtlich der thermischen und mechanischen Materialkennwerte von UHPC unter Brandeinwirkung. Auch das Abplatzverhalten von UHPC im Brandfall ist kritisch, sodass Losungsansatze zur Vermeidung zerstorender Abplatzungen gefunden werden mussen. In diesem Bericht werden Ergebnisse aus dem laufenden Forschungsvorhaben ,,Theoretische und experimentelle Untersuchungen zur Ermittlung und Optimierung des Brandverhaltens von ultrahochfestem Beton” vorgestellt. Dabei wird insbesondere auf die thermischen Materialkennwerte fur die Berechnung der Bauteilerwarmung und die mechanischen Materialkennwerte fur den Nachweis des Trag- und Verformungsverhaltens im Brandfall eingegangen, die in Anlehnung an Eurocode 2 Teil 1-2 temperaturabhangig hergeleitet werden.

Quantitative Comparison of International Design Standards of Escape Routes in Assembly Buildings

The design standards for escape routes in assembly buildings are discussed by comparing the building codes and regulations of eight European countries, China, and USA. To quantify the results for the simple scenario of the evacuation of an assembly room, the travel times are calculated by flow capacity equations. For each country the results vary with the area of the assembly room. Among different countries there is a significant scatter of the results which varies by a factor of three. As the travel times are influenced by the design occupant densities which range from 0.5 to 4 p/m2 for places of entertainment, a second comparison is made with a normalized density of 4 p/m2. Here the results also scatter by a factor of three. The implications on occupant safety are discussed with regard to potential fire scenarios.

Vorlesungsskripte im E-Learning-Zeitalter

In der universitaren Lehre dominieren Lernmaterialien, die hauptsachlich aus Text, Formeln, Tabellen und graphischen Illustrationen bestehen. Die Hersteller von E-Learning-Werkzeugen tragen dieser Tatsache jedoch nicht ausreichend Rechnung und bieten fast ausschlieslich Autorensoftware an, die auf die Erstellung von audiovisuellen Inhalten ausgerichtet ist. Obwohl sich die Integration von solchen textbasierten Inhalten in Lernplattformen und andere E-Learning-Systeme anbietet, fehlen bislang tragfahige Konzepte zur technischen Umsetzung. Zum einen mussen diese fachspezifische Anforderungen berucksichtigen, wie etwa ausreichende Unterstutzung fur mathematische oder chemische Formeln, und zum anderen sollen die erstellten Inhalte auch wiederverwendbar und moglichst plattformunabhangig sein. Im Rahmen dieses Beitrags diskutieren die Autoren zunachst mogliche Losungsansatze fur diese Problemstellung, im Weiteren stellen sie geeignete Werkzeuge fur die Inhaltserstellung vor und prasentieren schlieslich ihre Erfahrungen mit XML-basierter Inhaltserstellung im universitaren Praxiseinsatz.

Fire tests to validate fire simulation codes : experimental results

Abstract An “International Collaborative Project to Evaluate Fire Models for Nuclear Power Plant Applications” (ICFMP) has been started in 1999 to improve the reliability and the applicability of different fire models with respect to applications for nuclear plants. Within the frame of this project five benchmark exercises (BE) have been conducted from different organizations to represent various fire scenarios. Two of these five benchmark exercises (BE No. 4 and No. 5) have been performed at iBMB in Germany during 2002 and 2004. In BE No. 4 a large pool fire inside a compartment (with a volume of ≈ 76 m3) with respect to under-ventilated situations has been examined in a series of tests. In BE No. 5 four full scale cable tray fire tests have been performed in the same compartment, but with a different construction of the ceiling. The cable tray fire test series with vertically orientated cables considered pre-heating effects and includes time dependent electrical functional failure measurements. In this paper, an overview of the specification and of the experimental results of Benchmark Exercises No. 4 and No. 5 is given.

Das Risiko Feuer aus der Sicht von Wissenschaft und Technik

6 ZusammenfassungDie in erster Linie auf „übliche“ Gebäude zugeschnittenen gesetzlichen Brandschutzanforderungen erweisen sich bei baulichen Anlagen besonderer Art oder Nutzung oft als zu unflexibel. In solchen Fällen kann mit Hilfe ingenieurmäßiger Methoden das Brandrisiko individuell und optimal abgedeckt werden. Entsprechende wissenschaftliche Grundlagen sind vorhanden und werden im Rahmen der internationalen Brandschutzforschung mit Hochdruck weiterentwickelt. In der Praxis haben die aus theoretischen und experimentellen Untersuchungen abgeleiteten und durch Großbrandversuche und praktische Branderfahrungen bestätigten Berechnungsmodelle schon oft bei der Klärung strittiger Fragen weitergeholfen, wie in diesem Beitrag an drei Anwendungsbeispielen aus der eigenen Begutachtungspraxis demonstriert wird.Abschließend wird über die Entwicklung des rechnergestützten Systems SAFIR berichtet, in dem die derzeit verfügbaren Ingenieurmethoden nach dem Stand von Wissenschaft und Technik in einer Prozedurenbibliothek als Hilfsmittel für umfassende, risikogerechte Beurteilungen von Gebäuden besonderer Art und Nutzung implementiert sind. Für Beurteilungen auf „normalem“ Niveau sind die Brandschutzvorschriften nach dem Baurecht und die Brandschutzmaßnahmen nach dem geltenden Normenwerk in einer Regeldatei erfaßt. Schließlich bietet eine umfangreiche Datenbank mit Daten aus Brandberichten der Feuerwehr, aus Schadensakten von Feuerversicherern und aus Brandschutzgutachten von Sachverständigen eine Basis für statistische Aussagen im Rahmen einer Abschätzung des Brandrisikos anhand der Gebäudeart und -nutzung.