Filtern
Erscheinungsjahr
- 2016 (13) (entfernen)
Dokumenttyp
- Vortrag (6)
- Beitrag zu einem Tagungsband (5)
- Buchkapitel (2)
Schlagworte
- Offshore (3)
- Ballast (2)
- Bauwerksüberwachung (2)
- Concrete sleepers (2)
- Degradation (2)
- Pfahlgründungen (2)
- SHM (2)
- Track assessment (2)
- Track optimisation (2)
- Train-track-modelling (2)
Eingeladener Vortrag
- nein (6)
This paper deals with the assessment of track deterioration using a train-track interaction model. While modelling a train-track system a balance has to be found between the complexity and effort of the model on the one side and the needs for the assessment. The choice of assessment criteria are decisive for the given task. For an optimization of the track and its components simple assessment criteria are needed to allow for a variation of parameters. The paper describes the generalized process for track assessment and optimization and gives examples for specific members.
This paper presents a three dimensional numerical model which is can be used to
investigate the effects on the track and in its vicinity due to a train passage. The numerical
model for train track interaction is based on a time domain dynamic finite
element model. Due to the unbounded nature of the soil the truncated boundary of the
finite element domain is modelled with the scaled boundary finite element method,
which is a semi-analytical approach. The application for a heterogeneous track along
the track line is exemplified by a track with a bridge structure, where close attention
is paid to the wheel-rail contact force. The results indicate that the wheel-rail contact
force is not symmetrical around the bridge structure and an optimisation in terms of a
backfilling area and under-sleeper-pads can improve such a transition.
Suction Bucket Jackets (SBJ) are found as a suitable alternative to driven piles for the support of jacket or tripod foundations for offshore wind energy converters. Offshore wind energy turbines are characterized by a small self weight and they can be subjected to different load combinations. The work presented here aims to show the numerical investigation on the behavior of suction bucket foundations under different kind of loads as well as load combinations. In order to do so, a suitable numerical model is much needed. The theoretical basis of the model lies on the Swansea formulation of Biots equations of dynamic poroelasticity combined with a constitutive model that reproduces key aspects of cyclic soil behavior in the frame of the theory of generalized plasticity. An adequate FE formulation, the representation of appropriate soil-structure interfaces and the computational efficiency are key aspects in order to successfully model such complex systems. The 3D numerical simulation allows a special insight into the fundamental behavior of the founding of Suction Bucket Jackets such as the evolution of the pore water pressure or the occurrence of the so called soil liquefaction.
This paper deals with the assessment of track deterioration using a train-track interaction model. While modelling a train-track system a balance has to be found between the complexity and effort of the model on the one side and the needs for the assessment. The choice of assessment criteria are decisive for the given task. For an optimization of the track and its components simple assessment criteria are needed to allow for a variation of parameters. The paper describes the generalized process for track assessment and optimization and gives examples for specific members.
Fatigue is of relevance not only for metals but also for concrete. The current knowledge about fatigue behaviour of concrete is, however, incomplete. This concerns especially the progress of fatigue which precedes the fatigue failure. Some macroscopic effects of this process are well known but the governing material changes behind them are still less studied. The focus of the present contribution lay on a systematic and comprehensive investigation of the fatigue process under cyclic compressive loading. The aim was to obtain a deeper insight and to provide a better understanding of the damage process in the material. Cylindrical specimens were tested with a number of cycles to failure between 106 and 107. Various methods of non-destructive and destructive testing were used to investigate macroscopic and microscopic changes in the material. One main result was that the changes in the macroscopic material behaviour could not be explained only by the development of micro cracks. The results indicated that the related changes in the fatigue behaviour originate rather from viscous processes in the cement stone, similar to the process of creep. A sound description of the possible processes was derived from the obtained experimental results which concerns material structure during fatigue loading. It has been shown that in case of isotropic material behaviour a stiffness reduction related to a scalar value could not capture the damage effect on the stress-strain relationship caused by fatigue.
Schieflagen bitte vermeiden
(2016)
Vieles ist möglich, auch auf dem Meeresboden. Wind und Wellen rütteln gemeinsam an der Gründung, den Fundamenten der Offshore-Windenergieanlagen. Hinzu kommen die „ganz normale“ Strömung sowie die in der Nordsee besonders ausgeprägten Gezeiten von Ebbe und Flut. Zudem kann am Meeresboden Porenwasserüberdruck entstehen, der den Boden lockern und im schlimmsten Fall bei Monopiles die Stabilität der gesamten Anlage ändern kann. Selbst wenn ein solcher in den Meeresboden gerammter Pfahl bis zu 8 Meter Durchmesser hat. Über die Hälfte der geplanten Offshore-Anlagen in Nord- und Ostsee werden mit Ein-Pfahl-Gründungen geplant, über 40 % sollen als Mehrpfahl-Gründungen, zum Beispiel als Tripod, ausgeführt werden. Von daher verdienen Pfahlgründungen und ihre Belastungen besondere Aufmerksamkeit. Denn eines gilt es im Anlagenbetrieb unbedingt zu vermeiden: Eine drohende Schiefstellung der Anlage
Offshore-Windenergie betritt Neuland, gerade bei der Gründung. Denn Windenergie auf See kann die Erfahrungen der gängigen Offshore-Konstruktionen der Öl- und Gasindustrie nur bedingt nutzen. Mehr als dort, versucht man bei der Offshore-Windenergie, die Gründungsabmessungen – insbesondere die Pfahllängen – soweit wie möglich zu reduzieren. Denn dies kann bei der hohen Anzahl der Windenergieanlagen erhebliche wirtschaftliche Vorteile bringen. Andererseits wird die Standsicherheit der Gründungen durch den viel höheren Anteil an zyklischen Lasten gegenüber den gängigen Offshore- Strukturen in schwer einschätzbarer Weise zusätzlich gefährdet. Da Offshore-Windenergieanlagen in Serienfertigung produziert werden, wirkt sich hier jeder systematische Fehler bei der Gründung dann gleich als Serienfehler auf eine Vielzahl von Anlagen aus. Überwachung ist also angesagt – und das richtige Maß bei der Pfahlgründung, der am meisten verwendete Fundamenttyp bei Windenergieanlagen.
It is widely recognized that the dynamics of large civil structures, such as bridges or offshore structures, is significantly affected by temperature and other environmental influences. The most significant effect on the structural stiffness is due to temperature variations and especially due to the thermal gradients within the structures cross section. For civil engineering structures, changes in the dynamic response produced by varying environmental conditions can be equivalent or greater than the ones produced by damage.
Therefore, handling the environmental effects has become a major research field for global Structural Health Monitoring. A number of methods and techniques have been developed for addressing this issue for different civil engineering application examples.
An additional question is if temperature changes of stiffness correlate with a change in safety level of the structures bearing capacity which has to be discussed case dependent
In our contribution we show the result of an extensive literature review on the matter of varying temperature, describing the characteristic effects on the structure as well as the various approaches to that issue, including the experiences our work group has gained in the last 20 years of SHM on civil engineering structure.