Concrete Bridges in Germany
This article gives an overview over the state of th e art of concrete bridges in Germany. In addition t o the presentation of actual bridges projects (e.g. winners of German bri dge award) new trends in bridge construction and po st-tensioning technology will be presented. One is prestressing b y combining unbonded internal and external tendons which already had been realized at the pilot-projects Mühlenbergb rid e and Roßriether Graben-Bridge. Furthermore, th development and actual state of standards for the design concre te b idges are shown. At the moment the design is d one according to the German code DIN-Fachbericht 102 “Betonbrücken”.
Innovative technique for identification of prestressing tendons layout in post-tensioned bridges using a probe with MEMS accelerometer
Abstract Post-tensioned concrete bridges are currently often constructed engineering structures. In this type of bridges it is crucial that geometrical layout of prestressing system complies with the design requirements. Unfortunately, major errors still occur during assembly of tendon routes. This has often negative effects. In a local aspect, it may cause a local damage, such as spalling of concrete cover. In a global aspect, prestressing may produce distribution of forces in the bridge structure different from the expected. That is why numerous methods have been developed to control the accuracy of executed tendon routs. Some of them, e.g. geodetic measurements with levelers, require direct access to tendon sheaths. Other methods, which can be used after casting of concrete (mainly NDT methods) have a series of resolution, efficiency and accessibility limitations. Hence, the paper presents a proposal of an alternative method for control of tendons routing using a special probe with Micro Electro-Mechanical Systems capacitive accelerometer. The paper presents a concept of tests performed with the probe, evaluation of the probe application in the view of a random process and finally assessment of the results obtained with the use of the constructed measurement system in trial laboratory conditions.
Numerical tools applied to power reactor noise analysis
In order to be able to calculate the space- and frequency-dependent neutron noise in real inhomogeneous systems in two-group theory, a code was developed for the calculation of the Green's function (dynamic transfer function) of such systems. This paper reports on the development as well as the test and application of the numerical tools employed. The code that was developed yields the space-dependence of the fluctuations of the neutron flux induced by fluctuating properties of the medium in the two-group diffusion approximation and in a two-dimensional representation of heterogeneous systems, for both critical systems and non-critical systems with an external source. Some applications of these tools to power reactor noise analysis are then described, including the unfolding of the parameters of the noise source from the induced neutron noise, measured at a few discrete locations throughout the core. Other concrete applications concern the study of the space-dependence of the Decay Ratio in Boiling Water Reactors, the noise-based estimation of the Moderator Temperature Coefficient of reactivity in Pressurized Water Reactors, the modeling of the beam- and shell-mode core-barrel vibrations in Pressurized Water Reactors, and the investigation of the validity of the point-kinetic approximation in subcritical systems driven by an external source. In most of these applications, calculations performed using the code are compared with at-power plant measurements. Power reactor noise analysis applications of the above type, i.e. core monitoring without disturbing plant operation, is of particular interest in the framework of the extensive program of power uprates worldwide.