The Effect of Temperature Changes on Vertical Deflections of Metal Rail Bridge Constructions Determined by the Ground Based Radar Interferometry Method

Abstract

The paper describes possibilities of the relative new technique-ground based radar interferometry for precise determining of the effect of temperature changes on vertical deflections of metal bridge structures. The ground based radar interferometry method is used in practice, among other things, for the quick contactless determination of vertical deflections of metallic railway bridge structures. The precision in deflection determination is up to 0.01 mm in real time. At the same time, it is also possible to capture and analyze the oscillation frequencies of the monitored object with a maximum frequency of up to 50 Hz. Deflections are determined at multiple points of the object at the same time, for example on individual cross beams. This allows to obtain both general and detailed information about the behaviour of the structure under its dynamic load and to monitor the impact of vehicle passages or their groups. Moreover, the ground based radar interferometry method is not sensitive to temperature changes. It can therefore to be used successfully to determine the effect of temperature changes on deflections and deformations of metallic objects, such as bridge structures. The influence of temperature changes is of two kinds. First, a direct effect on the very structure causes deformations due to thermal expansion of the metallic material. Furthermore, it is the effect on the character of the dynamic deformations caused by load changes-the transit of vehicles. This character varies with temperature, as demonstrated by experimental measurement in practice. Practical examples from practice documented by experimental measurements are given in the article. For example, at a 75m long metal bridge over a six-hour period with a temperature change of 25°C, a vertical deflection-lifting the bridge deck was about 9.5mm due to the thermal expansion of the material. There has been also a change in the nature of the dynamic deflections caused by train passes. At low night temperatures (about 14°C), deflections were much smoother than at high afternoon temperatures (about 39°C).