Diagnostic load testing and assessment of existing bridges: examples of application

Load testing method is a significant tool in the assessment of bridge safety. One type of load tests is diagnostic load testing, the aim of which is to establish a comparison between real bridge behaviour and analytical calculation. It can be used either as acceptance test of the structures or as an estimation tool for the load carrying capacity of the already existing structures that have been in service for some time. This article presents diagnostic load tests and three examples of their application to various bridge structures and emphasises their diagnostic potential for assessment. In the majority of cases of diagnostic load tests presented in the literature, the experimental results (deflections, strains, etc) are very close or lower than the predicted ones and for this reason, such tests are expected to validate the existing structure. However, in the cases presented here, it is shown how the experimental results differ considerably from the expected ones. Since the theoretical and the experimental results of all three examples did not match, it was highly recommended to keep the matter under close investigation. A deep insight into the bridges showed serviceability and safety concerns and in some cases a repair/strengthening was necessary.