7.2 Ingenieurbau
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- 7.2 Ingenieurbau (43) (entfernen)
Eingeladener Vortrag
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Classic non-destructive fatigue crack detection methods reveal the state of the fatigue damage evolution at the moment of application, generally not under operational conditions. The here introduced crack luminescence method realizes a clear visibility of the occurred and growing crack in loaded components during operation. Different established experiments show that due to the sensitive coating a crack Formation can be detected even in early stage under the premise the crack reached the surface. The coating consists of two layers with different properties and functions. The bottom layer emits light as fluorescence under UV radiation. The top layer covers the fluorescing one and prevents the emitting of light in case of no damage at the surface. In case of surface crack occurrence, the luminescent light is clearly noticeable by visual observations and also by standard camera equipment which makes automated crack detection possible as well. It is expected that crack luminescence can increase structural safety as well as reduce costs and time for inspections and preventive maintenance.
Kontinuierliche sensorbasierte Bauwerksmessungen leisten einen wichtigen Beitrag zur Sicherheit von Verkehrsbauwerken. Hierzu werden im Vorhaben AISTEC Referenzbauwerke und Referenzverfahren untersucht mit Schwerpunkt auf den Einfluss klimatischer Bedingungen. Der Vortrag stellt den aktuellen Projektstand des FB 7.2 vor.
Die gesamte Prognose wurde rechnerisch erfasst. Die Rechenverfahren sind einfach und schnell. Die Emission und die Immission verwendet Übertragungsmatrizen. Die Transmissionsrechnung beruht auf der Dispersion der Rayleighwelle. Die Verknüpfung erfolgt über die Anregungskraft auf den Boden und über die Freifeldamplitude am Gebäude.
Es sind viele Eingabemöglichkeiten für Messdaten vorgesehen. Messungen können von einem Ort auf einen anderen Ort übertragen werden.
This paper proposes a novel method to estimate the lateral displacement of high-rise structures under wind loads. The coefficient β(x) is firstly derived, reflecting the relation between the structural lateral dynamic displacement and the inclination angle at the height x of a structure. If the angle is small, it is the ratio between the structural fundamental mode shape and its first-order derivative without influence of external loads. Several dynamic experiments of structures are performed based on a laser remote sensing vibrometer and an inclinometer, which shows that the fundamental mode is dominated in the structural displacement response under different types of excitations. Once the coefficient β(x) is curve-fitted by measuring both the structural lateral dynamic displacement and the inclination angle synchronously, the real-time structural lateral displacement under operational conditions is estimated by multiplying the coefficient β(x) with the inclination angle. The advantage of the proposed method is that the coefficient β(x) can be identified by lateral dynamic displacement measured in high resolution by the remote sensing vibrometer, which is useful to reconstruct the displacement accurately by the inclination angle under operational conditions
The erosion of natural sediments by a superficial fluid flow is a generic situation in many usual geological or industrial contexts. However, there is still a lack of fundamental knowledge about erosional processes, especially concerning the role of internal cohesion and adhesive stresses on issues such as the critical flow conditions for the erosion onset or the kinetics of soil mass loss. This contribution investigates the influence of cohesion on the surface erosion by an impinging jet flow based on laboratory tests with artificially bonded granular materials. The model samples are made of spherical glass beads bonded either by solid bridges made of resin or by liquid bridges made of a highly viscous oil. To quantify the intergranular cohesion, the capillary forces of the liquid bridges are here estimated by measuring their main geometrical parameters with image-processing techniques and using well-known analytical expressions. For the solid bonds, the adhesive strength of the materials is estimated by direct measurement of the yield tensile forces and stresses at the particle and sample scales, respectively, with specific traction tests developed for this purpose. The proper erosion tests are then carried out in an optically adapted device that permits a direct visualization of the scouring process at the jet apex by means of the refractive index matching technique. On this basis, the article examines qualitatively the kinetics of the scour crater excavation for both scenarios, namely, for an intergranular cohesion induced by either liquid or solid bonds. From a quantitative perspective, the critical condition for the erosion onset is discussed specifically for the case of the solid bond cohesion. In this respect, we propose here a generalized form of the Shields criterion based on a common definition of a cohesion number from yield tensile values, derived at both micro- and macroscales. The article finally shows that the proposed form manages to reconcile the experimental data for cohesive and cohesionless materials, the latter in the form of the so-called Shields curve along with some previous results of the authors which have been appropriately revisited.
A strain-based automated operational modal analysis algorithm is proposed to track the long-term dynamic behavior of a horizontal wind turbine under operational conditions.
This algorithm is firstly validated by a scaled wind turbine model, and then it is applied to the dynamic strain responses recorded from a 5 MW wind turbine system. We observed variations in the fundamental frequency and 1f, 3f excitation frequencies due to the mass imbalance of the blades and aerodynamic excitation by the tower dam or tower wake. Inspection of the Campbell diagram revealed that the adverse resonance phenomenon and Sommerfeld effect causing excessive vibrations of the wind tower.
Eindimensionale Modelle des Gleises aus einem Schienenstützpunkt, zweidimensionale Modelle enthalten die Kraftverteilung der Schiene. Eindimensionale Modelle machen einen Fehler, weil sie eine zu große Fahrzeugmasse berücksichtigen. Man kann jedoch bei der Berechnung der Minderungswirkung von Gleiselementen eindimensionale Gleismodelle verwenden, um die Kraftübertragung des Gleises bzw. die Minderungswirkung des Gleises zu berechnen. Die Wechselwirkung mit dem Fahrzeug kann einfach mit der dynamischen Stützpunktsteifigkeit berechnet werden. Dabei muss die Stützpunktsteifigkeit mit einer charakteristischen Gleislänge multipliziert werden, die frequenz- und systemabhängig ist.
The train passages over intact or damaged slab tracks on different soils have been calculated by the finite-element boundary-element or the wavenumber-domain method. The influence of track and soil parameters on the distribution of the track displacements and the soil forces has been analysed. The measured and calculated displacement time histories of train passages could be used to identify track damages such as lose sleepers or a lose track plate. The time histories and spectra of the soil forces can explain the measured ground vibration reduction of slab tracks. The calculated displacement and force distributions of slab tracks on continuous soils do not fulfil the Winkler hypothesis and Winkler models should not be used for track analysis.
This article deals with the relevance and practical feasibility of micromechanical simulations for their application to general geomechanical problems involving fluid-saturated granular assemblies, whether frictional or cohesive. A set of conceptual and numerical tools is here presented, advocating for a parallel computation using graphical processing units (GPUs) to treat large numbers of degrees of freedom with conventional Desktop computers. The fluid phase is here simulated with a particle-resolved approach in the frame of the Lattice Botzmann Method (LBM) while the granular solid phase is modelled as a collection of discrete particles from a Molecular Dynamics DEM perspective. The range of possible material behaviours for the solid granular phase is intended here to cover a broad spectrum from purely frictional to viscous cohesive materials with either brittle or transient debonding features. Specific details of the implementation and some validation cases are put forward.
Finally, some exemplary applications in the fields of soil erosion and geotechnical profile installation are provided along with a discussion on the parallel performance of the presented models. The results show that a micromechanical approach can be feasible and useful in practice, providing meaningful insights into complex engineering problems like the erosion kinetics of a soil under an impinging jet or the penetration resistance of a deep foundation in a layered soil profile.
The surface erosion of soil samples caused by an impinging jet can be analyzed using the jet erosion test (JET), a standard experimental test to characterize the erosion resistance of soils. This paper specifically addresses the flow characteristics of a laminar impinging jet over the irregular surface of granular beds to discuss the pertinence and relevance of commonly used empirical estimations based on a selfsimilar model of a free jet. The JET is here investigated at the microscale with a coupled fluid-particle flow numerical odel featuring the lattice Boltzmann method (LBM) for the fluid phase combined with the discrete element method (DEM) for the mechanical behavior of the solid particles. The hydrodynamics of a laminar plane free jet are confronted with the results from a parametric study of jet impingement, both on solid smooth and fixed granular surfaces, that take into account variations in particle size, distance from jet origin, and jet Reynolds number. The flow characteristics at the bed surface are here quantified, including the maximal values in tangential velocity and wall shear stress, which can be regarded as the major cause of particle detachments under hydrodynamic solicitation. It is shown that the maximal velocity at the impinged surface can be described by the free jet self-similar model, provided that a simple empirical coefficient is introduced. Further, an expression is proposed for the maximal shear stress in laminar conditions, including a Blasius-like friction coefficient that is inversely proportional to the square root of the jet Reynolds number. To conclude, finally, the JET erosion of different cohesionless granular samples is analyzed, confirming that the threshold condition at the onset of granular motion is consistent with the Shields diagram and in close agreement with previous experimental results.
The stability and geometric nonlinearities of slender structures are a major topic in structural design. While this topic is most relevant in the field of Structural Engineering, e.g. for steel or concrete structures, only few applications take the role of soil-structure-interaction explicitly into account. The focus of this paper is placed on the impact of soil support and its modelling for the buckling analysis based on examples both for pile foundations and for railway track stability. The general interaction between steel design and the geotechnical input will be addressed. The paper discusses and summarizes a range of subtopics based on experience and current research at the author’s institute.
Reliability analysis of deteriorating structural systems requires the solution of time-variant reliability problems.
In the general case, both the capacity of and the loads on the structure vary with time. This analysis can be approached by approximation through a series of time-invariant reliability problems, which is a potentially effective strategy for cases where direct solutions of the time-variant reliability problem are challenging, e.g. for structural systems with many elements or arbitrary load processes. In this contribution, we thoroughly Review the formulation of the equivalent time-invariant reliability problems and extend this approximation to structures for which inspection and monitoring data is available. Thereafter, we present methods for efficiently evaluating the reliability over time. In particular, we propose the combination of sampling-based methods with a FORM (first-order reliability method) approximation of the series system reliability problem that arises in the computation of the lifetime reliability. The framework and algorithms are demonstrated on a set of numerical examples, which include the computation of the reliability conditional on inspection data.