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This paper addresses how the value of damage detection Information depends on key Parameters of the Structural Health Monitoring (SHM) system including number of sensors and sensor locations. The Damage Detection System (DDS) provides the information by comparing ambient vibration measurements of a (healthy) reference state with measurements of the current structural system. The performance of DDS method depends on the physical measurement properties such as the number of sensors, sensor positions, measuring length and sensor type, measurement noise, ambient excitation and sampling frequency, as well as on the data processing algorithm including the chosen type I error for the indication threshold. The quantification of the value of Information (VoI) is an expected utility based Bayesian decision analysis method for quantifying the difference of the expected economic benefits with and without information. The (pre-)posterior probability is computed utilizing the Bayesian updating theorem for all possible indications. If changing any key parameters of DDS, the updated probability of system failure given damage detection information will be varied due to different indication of probability of damage, which will result in changes of value of damage detection information. The DDS system is applied in a statically determinate Pratt truss bridge girder. Through the analysis of the value of information with different SHM system characteristics, the settings of DDS can be optimized for minimum expected costs and risks before implementation.
This paper addresses the effects of the deterioration on the value of damage detection information. The quan-tification of the value of damage detection information for deteriorated structures is based on Bayesian pre-posterior decision analysis, comprising structural system performance models, consequence, benefit and costs models and damage detection information models throughout the service life of a structural system. The value of damage detection information accounts for the relevance and precision of the information to ensure the structural integrity and to reduce the potential structural system risks and expected costs throughout the ser-vice life before implementing damage detection system. With the developed approach, the value of damage detection information for a statically determinate Pratt truss bridge girder subjected to different deterioration models is calculated. The analysis shows the impact of the deterioration model parameters on the value of damage detection information. The results can be used to develop optimal maintenance strategies before im-plementation of the damage detection system.
In this paper, a nonlinear three-dimensional finite element (FE) model was developed and validated to study the effect of seismic damage location on the response of concrete filled tube (CFT) columns at fire after earthquakes. Three analyses were conducted consecutively in the modelling, namely, cyclic, thermal and structural. Results of the cyclic loading analysis comprising residual deformations were applied as the Initial condition to the thermal-stress model, replicating the seismic performance of column.
Following, a nonlinear sequentially coupled-thermal stress Analysis was carried out to investigate the fire response of CFT columns after the seismic event. Three damage scenarios were contemplated, considering any possible potential damages that could be generated by the earthquake loading on CFT columns. The accuracy of the proposed FE model was examined by comparing the numerical results with that of available tests on fire and cyclic loading. By means of the validated model, the performance of damaged CFT columns was then investigated under fire after earthquakes. The level of damage was assumed as a high damage level, presuming that the column reached 50% of ist lateral resistance while still maintaining its overall stability after the earthquake. The results were presented broadly, including the axial deformation history as well as the fire resistance time for CFT columns. To have a comprehensive insight on the influence of damage location in columns, the fire response of damaged specimens was compared with that of an intact one.
Die Grundidee einer Schwingungsminderung ist es eine tiefe Eigenfrequenz der Struktur zu erreichen, so dass höhere Frequenzen abgemindert werden. Das gilt für die Minderung an der Quelle, zum Beispiel einem Eisenbahngleis, und für die Minderung am Empfänger, dem Gebäude. Die Eigenfrequenz ermittelt man aus dem Verhältnis der Auflagersteifigkeit und der Masse. Wie ist die Masse bei einem Gebäude zu wählen? Und wie ist die Untergrundsteifigkeit zu berücksichtigen? Als Referenzsituation ohne Minderungsmaßnahme? Der Beitrag bringt Rechenergebnisse zu abgefederten Gebäuden mit einfachen und komplexen (FE-) Modellen, Mess- und Rechenergebnisse zur Schwingungsübertragung von unabgefederten Gebäuden. Es wird der Einfluss der Abstimmfrequenz, der Bodensteifigkeit und der „starren“ Gebäudemasse untersucht. Die komplexen Gebäudemodelle erlauben, neben der Berechnung einer elastischen Gebäudelagerung, auch die Variation von Gebäudeparametern zur Reduktion der Deckenschwingungen. Den Ergebnissen bei der Erschütterungs-übertragung in Gebäude werden zwei ähnliche Beispiele zur elastischen Maschinenlagerung und zur elastischen Gleislagerung gegenübergestellt.
Evaluation of evacuation process is common separated by two phases: pre-movement and movement-phase. Individual capabilities of pedestrians have an impact on both and therefore on the time required for safe escape. In view of evaluating the evacuation process, characteristics of realistic movements of pedestrians involved are needed, but so far such data are mainly available for individuals with unrestricted evacuation capabilities only.
Due to the lack of available data, parameter studies in an assisted living for people with disabilities were performed to explore the movement during evacuation. Preparation times for assistance (n=10), unimpeded walking speeds (n=34) depending on the assistance devices in the plane as well as walking speeds on stairs (n=11) were focussed.
Time to prepare an assistance device for utilisation depends significantly on the kind of device type. Further on, practical experience in handling the devices for assistance has an impact on the preparation time. In contrast to the results of the preparation times, any relation on assistance devices were investigated for the unimpeded walking speed in the plane. A remarkable decrease of walking speed on stairs was observed which is independent from the utilised assistance device.
The presented data improve and extend the insufficient engineering data base and raised up questions regarding the complexity of considering pedestrians movement with impairments in evacuation planning.
Fires in road tunnels constitute complex scenarios with interactions between the fire, tunnel users and safety measures. More and more methodologies for risk analysis quantify the consequences of these scenarios with complex models. Examples for complex models are the computational fluid dynamics model Fire Dynamics Simulator (FDS) and the microscopic evacuation model FDS+Evac. However, the high computational effort of complex models often limits the number of scenarios in practice. To balance this drawback, the scenarios are often simplified. Accordingly, there is a challenge to consider complex scenarios in risk analysis.
To face this challenge, we improved the metamodel used in the methodology for risk analysis presented on ISTSS 2016. In general, a metamodel quickly interpolates the consequences of few scenarios simulated with the complex models to a large number of arbitrary scenarios used in risk analysis. Now, our metamodel consists of the projection array-based design, the moving least squares method, and the prediction interval to quantify the metamodel uncertainty. Additionally, we adapted the projection array-based design in two ways: the focus of the sequential refinement on regions with high metamodel uncertainties; and the combination of two experimental designs for FDS and FDS+Evac.
To scrutinise the metamodel, we analysed the effects of three sequential refinement steps on the metamodel itself and on the results of risk analysis. We observed convergence in both after the second step (ten scenarios in FDS, 192 scenarios in FDS+Evac). In comparison to ISTSS 2016, we then ran 20 scenarios in FDS and 800 scenarios in FDS+Evac. Thus, we reduced the number of scenarios remarkably with the improved metamodel. In conclusion, we can now efficiently integrate complex scenarios in risk analysis. We further emphasise that the metamodel is broadly applicable on various experimental or modelling issues in fire safety engineering.
Quenching and partitioning (Q&P) heat Treatment increases the deformability of high-strength martensitic steels. Therefore, it is necessary to have some metastable austenite in the microstructure, which transforms in martensite during plastic deformation (TRIP effect). The austenitic-martensitic microstructure is gained by an increased austenitization temperature, water quenching and additional partitioning. The partitioning enables local carbon diffusion, which stabilizes retained austenite and leads to partial reversion of martensite to austenite. The influence of partitioning time was studied for the martensitic stainless steel AISI 420 (X46Cr13, 1.4034). In line with these efforts, metallographic, XRD and EBSD measurements were performed to characterize the microstructural evolution. The mechanical properties were tested using tension and compression loading. Additional corrosion investigations showed the benefits of Q&P heat treatment compared to conventional tempering. The reversion of austenite by the partitioning treatment was verified with EBSD and XRD. Furthermore, the results of the mechanical and corrosion testing showed improved properties due to the Q&P heat treatment.
Remediation of Cracks Formed in Grouted Connections of Offshore Energy Structures under Static Loads
(2018)
The future energy demand necessitates the exploration of all potential energy sources both onshore and offshore. Global trend has shifted towards offshore energy, which can be obtained from either carbon intensive or renewable options, hence requiring structures such as rigs, platforms, and monopiles. Most of these structures adopt easily installable construction techniques, where lower foundation need to be connected with the super structure by mean of grouted composite joints. Generally, these composite connections have exterior sleeve, interior pile and infill grout. Being located in remote offshore conditions, connections can experience considerable adverse loading during their lifetimes. Degradations were reported inside similar connections, which were installed in last three decades. Besides, grouting in the offshore sites may often be proven difficult, which eventually leads to reduced capacity of connections in the long run. Thus, repair and rehabilitation of such connections should be planned ahead to minimize operational delays and costs in the future. This study aims at characterizing the nature of crack generation in grouted connections and thereby identifying the potential of repair using suitable repair material. Scaled grouted joints were manufactured using a novel mold, and connections were loaded under static load to visualize the main failure pattern. The failure mechanism and loading capacity are found compatible to previous results from earlier literature. Grouted connection was then repaired using cementitious injectable grout. The effectiveness of the repair system is also discussed.
Die Erkenntnisse zu reaktiven Brandschutzsystemen (RBS) werden kontinuierlich erweitert, was sich in der Entwicklung neuer Produkte und der Ausweitung des durch technische Regelungen abgedeckten Anwendungsbereichs äußert. Der hier vorliegende Beitrag konzentriert sich auf die Verwendung von RBS auf Stahlkonstruktionen. In den vergangenen zehn Jahren wurden, abgesichert durch neue Erkenntnisse aus der Forschung, die Anwendung auf Stahlzuggliedern mit offenem Profil präzisiert und im Rahmen allgemeiner bauaufsichtlicher Zulassungen (abZ) neu geregelt. Ferner wurde die Grundlage geschaffen, die Anwendung von RBS auf Zuggliedern mit kreisrundem Vollprofil zu bewerten und auf Basis der abZ zu ermöglichen.
Neben einer umfassenden Darstellung der aktuellen nationalen und europäischen Regelungen zu RBS, werden technologische Besonderheiten und deren Einfluss auf den Regelungsinhalt im Beitrag thematisiert.
In der jüngsten Vergangenheit stellt sich mit zunehmender Dringlichkeit die Frage nach der Bewertung der Dauerhaftigkeit von RBS für lange Zeiträume, wobei damit Nutzungsdauern weit jenseits der in den nationalen und europäischen Regelungen bereits etablierten 10 Jahre gemeint sind. In diesem Zusammenhang ist zu klären, wie der Feuerwiderstand von Konstruktionen zu bewerten ist, die bereits über lange Zeiträume mit RBS versehen sind. Nicht zuletzt stellt sich die Frage nach der Dauerhaftigkeit der Systeme selbst und adäquaten Prüfverfahren zu deren Beantwortung. Neue und bereits etablierte
Ansätze werden vorgestellt und diskutiert.
Der Beitrag schließt mit einer Darstellung der aktuellen Forschung. Neben den Forschungsaktivitäten zur Dauerhaftigkeit sind hier insbesondere Untersuchungen zur Anwendung und Bewertung von RBS auf Grundlage von Naturbränden und extremen Brandereignissen genannt. Neuste Untersuchungen befassen sich auch mit der Anwendung von RBS auf komplexen Geometrien wie auch auf anderen Substraten wie Beton, Aluminium und faserverstärkten Kunststoffen sowie hybriden Werkstoffen. Die hybriden Werkstoffe aus der Kombination von Metallen und Verbundwerkstoffen sind derzeit vorwiegend im Behälter-, Fahrzeug- und Flugzeugbau anzutreffen. Auch die bereits vor Jahrzehnten begonnenen Aktivitäten zur Entwicklung rechnerischer Verfahren zur Beurteilung der Wirkungsweise von RBS werden in der aktuellen Forschung fortgeführt und weiterentwickelt.