ABSTRACT
There were detailed investigation made on the three Polish bridges – the Zakroczym bridge, the Nur bridge and the Kaczawa bridge.
The investigation scenario was moreover similar in all three cases, however the Zakroczym bridge was under special surveillance including inside temperature and humidity monitoring, due to its extraordinary box cross section. There was a dedicated automatic monitoring system installed. It was to register the climate condition inside and outside the box girder. For nearly two years, five gauges measuring humidity and ten measuring temperature (half of them were measuring the steel surface temperature and half the air temperature) every ten minutes was monitoring and recording measured values. The cyclical structure assessment revealed that one of the steel of one bridge span did not create proper patina layer neither after three years of service nor after five years since it was produced. The girder surface was covered with thick, brittle layer of corrosion products, which were tearing apart exposing bare steel surface, which was not protected with the patina again. The specimens were examined in periodical time space, so there is a possibility to trace the particular value variation in the time. The investigation revealed two main reasons of the steel behavior.
