Erfahrungen bei der Beurteilung der Dauerhaftigkeit vorgespannter Bewehrung von älteren Spannbetonbrücken

Experiences due to the evaluation of the durability of prestressed reinforcements in old prestressed concrete bridges. Old prestressed concrete bridge superstructures exhibiting cracks across the prestressed reinforcement need detailed inspections for estimating maintenance requirements. Only this type of evaluation makes it possible to determine the required extent and nature of maintenance. In this paper essential steps of the “Directive of the durability of prestressed reinforcements in old prestressed concrete bridge superstructures” of the Federal Highway Research Institute are explained, also against the effects of growing heavy traffic with expected higher gross weights and axle loads.     

Modellkorrekturfaktoren als “Performance Indikatoren” für die Langzeitbewertung der integralen Marktwasserbrücke S33.24

Monitoring hat für den Entwurf und die Beurteilung sowohl neuer als auch bestehender Ingenieurtragwerke eine enorme Wichtigkeit. Die praktische Erfahrung und Beobachtungen zeigen, dass Monitoring die Grundlage für neue normative Grundlagen oder effiziente Erhaltungsprogramme liefern kann. Darüber hinaus können Monitoringsysteme erhebliche Instandsetzungskosten und Unannehmlichkeiten infolge von Störungen vermeiden. Dies begründet den erheblichen Forschungsaufwand, um eine effektive Implementierung der aufgenommenen Monitoringdaten in ein numerisches oder analytisches Strukturmodell zu erreichen, welches die Ermittlung eines vom erwarteten Verhalten abweichenden Strukturverhaltens und die Entdeckung eines beginnenden Verschlechterungsprozesses erlaubt. Dieser Aufsatz behandelt ein Konzept für eine effektive Einbindung einer Monitoringinformation in ein numerisches Modell auf Basis des Konzeptes der Modellkorrekturfaktoren. Insbesondere entstand diese Studie aus den Fragestellungen im Zuge des Forschungsprojektes “Monitoringbasierte Analyse von Integralen Brücken (MAIB)”. Das Forschungsvorhaben MAIB verfolgt Fragestellungen, welche das Tragwerk, die Interaktion zwischen Tragwerk und Bodenkörper, die Stabilität des Bodenkörpers hinter dem Widerlager und den Übergangsbereich zwischen dem Tragwerk und dem Boden im Fahrbahnbereich betreffen. Monitoring and Influence Lines Based Performance Indicators Monitoring is of most practical significance for the design and assessment of new as well as of existing engineering structures. Practical experience and observations show that monitoring can provide the basis for new code specifications or efficient maintenance programs. Moreover, monitoring systems can avoid considerable costs of repairs and inconvenience to the public due to interruptions. This gives rise to the need for a thorough investigation to achieve an effective implementation of recorded monitoring data in numerical or analytical structural models that allow the detection of a deviant behavior from the proposed and the detection of initial deterioration processes. This study attempts to derive a concept for the effective incorporation of monitoring information in numerical models based on the concept of model correction factors. In particular, these studies are performed on the abutment free bridge structure S33.24 that has been proof loaded in February 2010 and monitored since December 2008. A merit of models derived based on monitoring data is that they are directly related to performance indicators which can be used for the assessment of the existing structural capacity and for an efficient life cycle analysis.     

Dynamische Verformungsmessungen an Eisenbahnbrücken mittels Mikrowelleninterferometrie

Dynamic measurements of railway bridge displacements through microwave interferometry – Part 1: measurement method The microwave interferometry is a rather new measuring technique, yet little‐known in civil engineering applications. It allows the non‐contact acquisition of structural displacements with accuracy in the sub‐millimetre range at a sampling rate of up to 4 kHz. The high sampling frequency allows also the caption of dynamic structural responses, which can be used for a straightforward determination of the main modal parameters of the structures (natural frequencies, damping ratios). Furthermore, the synchronous acquisition of the overall motion of the targeted object is possible due to a high range resolution, which facilitates a direct identification of modal shapes. This paper gives a short introduction of the measurement method and outlines its boundary conditions and limitations with respect to applications in railway bridge dynamics. The knowledge has been gained on the basis of comprehensive systematic experimental investigations performed within the frame of a cooperation project with the German Railways (Deutsche Bahn AG). As a result an evaluation matrix was created, which clearly illustrates the applicability of the microwave interferometry for different railway‐specific tasks. The second part will present selected results of microwave interferometry measurements of railway bridges in comparison to parallel conventional measurements and the corresponding numerical investigations, which were used for the validation of the measurement technique.