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The Measurement- and Model-based Structural Analysis (MeMoS) integrates a finite element model into least squares adjustment and thus allows to evaluate a mechanical model and measurements in a combined analysis. To examine the capability to detect and localise damage using this integrated analysis MeMoS, a small-scale truss bridge made of aluminium profiles is built as a test specimen for this purpose.
The determination of material parameters from displacement field measurement is being examined for linear elastic solid. A frequently used approach to compute material constants can be found in many studies. Even though they presented the approach in many different variations, but in the end they are essentially based on the same algorithm: Parameters are iteratively tuned until the computed results are in accordance with the measurements. The main drawback of this approach is that mainly commercial software is used that hinders us to investigate its inner evaluation process. This leads to the question, how the results from this commercial software can be trusted. On the contrary to these debatable approaches, we present a method that inverts the procedure of finite element method by using the most general model for a least-squares adjustment – the GAUSS-HELMERT Model.
The integration of finite element method (FEM) into the least-squares adjustment presented in [1] is further extended for a joint evaluation of an elastostatic model and displacement field measurement. For linear solids which obey the HOOKE's law, the material parameters determination from measurements is being examined. In many literature, see for example [2], parameters are iteratively tuned until the computed FEM results are in accordance with the measurements. In contrast to these debatable approaches, we follow a rigorous and direct method. The “classical” FEM procedure starts with known material constants and ends up with computed fields such as dis-placement or temperature field. We present a method to invert the FEM procedure using the most general least-squares adjustment – the GAUSS-HELMERT Model (GHM). From given fields, the material parameters are directly calculated.
By means of a small-scale truss bridge, the ability of the Measurement- and Model-based Structural Analysis to detect and localise damage was examined in. Although there was no noteworthy difficulty in detecting damage, it turned out that damage localisation responds sensitively to systematic influences, i.e. non-modelled properties of the mechanical model. Therefore, another experiment is being conducted to re-examine the Measurement- and Model-based Structural Analysis. For this purpose, the bending test is carried out as it has been already theoretically respectively numerically discussed in. In this attempt, the systematic influences such as residual stress are kept as low as possible.
By means of a small-scale truss bridge, the ability of the Measurement- and Model-based Structural Analysis to detect and localize damage was examined. Although there was no noteworthy difficulty in detecting damage, it turned out that damage localization responds sensitively to systematic influences, i.e. non-modelled properties of the mechanical model. Therefore, another experiment is being conducted to re-examine the Measurement- and Model-based Structural Analysis. For this purpose, the bending test is carried out as it has been already theoretically respectively numerically discussed. In this attempt, the systematic influences such as residual stress are kept as low as possible.
Many engineering structures are nowadays made of composite materials or metal foam. These modern engineering materials contain very complex inner geometry. To simulate the deformational behaviour of these structures often requires a high number of discretisation elements. This in turn yields a very large system of linear equations that are extremely time and memory consuming or practically impossible to solve. It is therefore desirable to find an approach to overcome this obstacle. In this paper a numerical method is proposed to find an approximate substitute model for geometrical complex structures.
To examine the capability to detect and localise damage using the Measurement- and Model-based Structural Analysis (MeMoS), a small-scale truss bridge (1520 mm × 720 mm × 720 mm) made of aluminium profiles is built as a test specimen for this purpose. The truss frame of the test bridge is made of aluminium profiles with a sophisticated design of the cross-sectional area. In comparison, with solid profiles, only a fraction of the material is needed to produce the profiles, while their bending resistance decreases slightly. The profiles are built into a truss frame by connecting them by means of fastening sets made of steel. The bridge model is mounted on four steel bearings which each of them consist of a cylinder arranged between two plates. Fixed bearings are made by holding onto one end of the bridge. The bridge is subjected by an external load by placing a heavy object beneath it. At the same time, measurements can be conducted below the bridge. Therefore, the bridge specimen is elevated by attaching it on a pedestal with four columns. Damages can be induced by loosening the fastening pieces.
One major ambition in Structural Health Monitoring (SHM) is to develop the ability to detect, identify and localize damage as well as to predict the lifespan of civil structures (Worden et al. 2007). This would allow well-informed decision on whether to repair or to demolish these structures. The word monitoring in SHM brings up several frequently ignored questions: What type of sensors and accuracies are needed to monitor a given structure? Where are the optimal sensor placements? How many sensors are necessary? How to analyse spatially distributed hybrid measurements? Or, in short: What is the sensor configuration best suited for structural health monitoring? If these questions are not explicitly addressed, the usefulness of the measurement data for an evaluation is left to coincidence.
Integration der Finite-Elemente-Methode in die Ausgleichsrechnung zur Parameteridentifikation
(2014)
Die Strukturüberwachung von Ingenieurbauwerken beruht heutzutage auf einer Auswertung räumlich und zeitlich verteilter hybrider Messungen, die z. B. mittels Tachymeter, Neigungssensoren, faseroptischen Sensoren (FOS), Dehnmessstreifen (DMS), GPS etc. erfasst werden. Für eine gemeinsame Auswertung müssen neue Methoden adaptiert werden, da diese, wie Lienhart (2012) aufzeigt, nur unter Verwendung eines mechanischen ‘Bauwerkmodells erfolgen kann.
In vielen Ingenieurwissenschaften, wie z. B. dem Bauingenieurwesen, findet die Modellierung physikalisch-mechanischer Eigenschaften von Strukturen mithilfe der Finite-Elemente-Methode (FEM) statt. Die Verifizierung eines derartigen Modells erfolgt vorwiegend lediglich durch stellenweise Messung von z. B. Durchbiegungen und einer anschließenden Gegenüberstellung mit den berechneten Modellwerten. Dies ist meist der Tatsache geschuldet, dass für die FE-Modellierung in der Regel kommerzielle Programme verwendet werden, und somit auf viele Teilprozesse des Auswertealgorithmus nicht zugegriffen werden kann. Aus diesem Grund erfolgt in vielen akademischen Fragestellungen die FE-’Modellierung mit Open-Source-Software, wie z. B. FEniCS (2013) oder OpenSees (2013), wodurch auch eine kombinierte Auswertung von Messungen und Modell nach der Methode 'der kleinsten Quadrate ermöglicht wird.
In diesem Beitrag wird eine messungs- und modellbasierte Strukturanalyse (MeMoS) durch (die Integration der Finite-Elemente-Methode in die Ausgleichungsrechnung am Beispiel eines Vier-Punkt-Biegeversuchs vorgestellt. In numerischen Untersuchungen wird gezeigt, wie diese integrierte Analyse für eine Parameteridentifikation angewendet werden kann. Für diese Untersuchungen wird ein Finite-Elemente-Modell mit bekannten Randbedingungen und Materialeigenschaften aufgestellt. Die Durchbiegungen, die als Beobachtungen in die Ausgleichung eingehen, werden mithilfe von Simulationsrechnungen erzeugt; der zu fidentifizierende Parameter ist der Elastizitätsmodul eines Balkens.
Es wird untersucht, mit welcher Genauigkeit Durchbiegungsmessungen durchgeführt werden müssen und an welcher Stelle des Bauwerks diese Messungen erfolgen sollen, um den Elastizitätsmodul möglichst genau zu bestimmen. Des Weiteren wird der Einfluss der Anzahl der Messstellen auf den zu identifizierenden Parameter untersucht.
