Verringerung des Temperatureinflusses bei der Überwachung von Brücken am Beispiel von Messdaten aus Luxemburg

Conference given outside the academic context (2021)

A rising number of concrete bridges are showing increasing damage due to corrosion and fatigue. In addition to the regular standard visual inspection, the bridge’s condition can also be recorded using ... [more ▼]

A rising number of concrete bridges are showing increasing damage due to corrosion and fatigue. In addition to the regular standard visual inspection, the bridge’s condition can also be recorded using additional tests with repeated static loading and/or dynamic tests. To determine any damage to a structure and to check its structural stability, it is crucial to know the exact system properties of the bridge in its undamaged reference state. The system behavior is influenced by damage and bearing conditions and environmental influences, such as the structure’s temperature. The influence of temperature can even cause larger changes in the measured quantities (bending line or modal parameters) than real damage. Therefore, temperature effects should be compensated before any condition analysis. The present work aims to demonstrate the influence of different bearing types and temperature on a real bridge beam. For this purpose, various static and dynamic tests were performed in the undamaged reference state. [less ▲]

REFERENCE MEASUREMENTS AND SIMULATIONS OF STATIC AND DYNAMIC CHARACTERISTICS OF PRESTRESSED CONCRETE BRIDGES UNDER OUTDOOR CONDITIONS FOR STRUCTURAL HEALTH MONITORING

Doctoral thesis (2021)

Today’s traffic infrastructure, including its engineering structures such as bridges, is stressed not only by natural ageing and corrosion but also by fatigue. The fatigue of material is accelerated by ... [more ▼]

Today’s traffic infrastructure, including its engineering structures such as bridges, is stressed not only by natural ageing and corrosion but also by fatigue. The fatigue of material is accelerated by the steadily growing traffic volume and heavier vehicles. Many bridges were built after World War 2 using the prestressed concrete construction method that emerged at that time. Some bridges are close to the end of the planned service life and show damage such as spalling, cracking and corrosion. In addition, some bridges have not yet reached the end of their planned service life and already exhibit damage. These bridges require special attention and control, knowing that this issue is highly safety and cost relevant at the same time. Structural Health Monitoring (SHM) of bridges aims to detect and localise damage as early as possible to take countermeasures to reach at least the planned service life or even more. Therefore, control systems are needed to support the engineers in addition to the visual bridge inspection. Permanent control systems can allow real time controlling of the bridge behaviour but generate high effort and cost. One approach in SHM is damage detection based on stiffness changes. Damage can alter both the static and modal properties of a structure. It leads to a loss of stiffness and, consequently, to greater static deflection and, in dynamics, to a decrease of eigenfrequencies. A prerequisite for early damage detection is essential information about the bridge structure, best knowledge and understanding of the individual bridge behaviour already in the undamaged state to track changes. This information can be obtained with experiments on a bridge and, in parallel, by simulation with a Finite Element (FE) model. In the next step, the FE model is updated to the measurements so that the reference state of the structure is well matched. The aim of the simulation is not the ultimate load bearing analysis, but the simulation of changes in the deflection line, eigenfrequencies, mode shapes and in the best case, also in the static or dynamic flexibility matrix and even better stiffness matrix due to damage. For this purpose, recurring measurements and simulations are compared with the initial measurements. If changes in the properties occur, model updating can be used to detect, localise and quantify damage. For the described approach, the detection and localisation of damage depend on the best possible reference state’s characteristics acquisition. The most commonly used construction method for bridges is prestressed concrete. Therefore, the main focus of this work is the recording of the undamaged reference state of a post tensioning bridge beam. The test object was a 26 m long prestressed concrete T-beam, which was saved before the demolition of the real bridge. It was subsequently installed outdoors on the campus of the University of Luxembourg as a simple supported real size test beam. Since the changes in static and dynamic system properties are not only due to damage but can also occur, for example, as a result of temperature fluctuations, the work focuses as well on the recording and assessment of influences arising from bearing and real environmental conditions in the undamaged reference state. For the temperature acquisition, the tests were carried out over around 2 years. Moreover, the influence of bearing conditions was tested by three interchangeable movable bearing types. The reference condition was recorded by static, quasi-static and dynamic tests. Throughout the observation period, the temperature and deflection of the bridge were continuously measured at different positions. For the deflection measurements, a commercial system was used that requires contact with the bridge. In addition, two new non-contact measurement approaches were tested. One is a camera-based system and the other is a laser-based system. The laser-based measurement method was improved during the recordings and tested by a second laser based system at the beam. Through the various tests, the deflections, eigenfrequencies and mode shapes of the bridge were determined. With the information of the experimental part, an FE model was created and best fitted to the reference state. The FE model consists mainly of solid elements. For a future model updating, a special FE model was created, offering a slice-by-slice adjustment of the beam stiffness. The model was used to perform static deformation and modal analysis. Then, the static and dynamic flexibility matrix was calculated and compared based on the experimental and numerical results. Finally, and in view of the subsequent artificial damage of the beam, damage scenarios are proposed based on the calculated cracking moment. [less ▲]

Neuere Methoden zur Identifikation und Lokalisierung von Schäden an vorgespannten Betonbrücken

in Bischoff, Manfred; von Scheven, Malte; Oesterle, Bernd (Eds.) Baustatik-Baupraxis 14 (2020, March 23)

Zuerst wird ein rein statistischer Schadensindikator basierend auf der Hauptkomponentenanalyse vorgestellt. Wichtig sind Referenzmessungen im ungeschädigten Zustand, um Veränderungen zu identifizieren ... [more ▼]

Zuerst wird ein rein statistischer Schadensindikator basierend auf der Hauptkomponentenanalyse vorgestellt. Wichtig sind Referenzmessungen im ungeschädigten Zustand, um Veränderungen zu identifizieren. Bevor die Messdaten mit den Rechenmodellen kombiniert werden, müssen Temperatureffekte kompensiert werden, um dann die Schäden zu erkennen und zu lokalisieren. Ein „Model-Updating“ Prozess eines speziellen Finite-Elemente- Modells passt die Steifigkeitsmatrix an die gemessenen Eigenfrequenzen oder an die progressive Absenkung unter Eigengewicht an. [less ▲]

Modeling of a prestressed concrete bridge with 3D finite elements for structural health monitoring using model updating techniques

in ISMA2018 International Conference on Noise and Vibration Engineering (2018)

This paper presents a linear finite element model for a prestressed concrete beam, which was part of a real bridge. Static and dynamic tests were carried out and compared to the numerical simulation ... [more ▼]

This paper presents a linear finite element model for a prestressed concrete beam, which was part of a real bridge. Static and dynamic tests were carried out and compared to the numerical simulation responses. A solid finite element model was created including the prestressed concrete beam, permanent dead load, two additional live loads and a shaker. A well planned finite element model is very important for later detection and localization of damage. Therefore, a mapped mesh was used to define so-called ‘slices’, which enables describing stiffness changes, e.g. damage. The model validation was performed by comparing simulated results to measured responses in the healthy state of the beam. After validation of the reference model, it is possible to modify the bending stiffness along the longitudinal axis of the beam by modifying Young’s moduli of different slices to adapt for the effect of damage. [less ▲]