Assessment of an Old Steel Railway Bridge Using Dynamic Tests.

Abstract

The paper describes an experimental analysis of more than one hundred years old railway bridge in the Czech Republic. It spans over the Vltava river and Orlík dam. Recently, the bridge was subjected to the extensive assessment of the load capacity and the general condition. The results of the assessment showed, that the corrosion in the important details, insufficient horizontal stiffness, together with insufficient stability for the wind and unloaded train load were the most critical problems. Based on those findings, the large static, dynamic and brake load tests were proposed to be done. It was mainly focused on measurement of strains ad acceleration in critical locations on the steel structure. These accelerometers were also used for ambient vibration measurement to assess the basic natural frequencies and mode shapes of the bridge. The last tests were the brake and acceleration tests, focused on verification of the real brake forces of the train. The results were compared with theoretical predictions to verify the FE model of the bridge. The vertical accelerations were high but acceptable with respect to the character and the age of the structure, while horizontal vibrations were very high and uncomfortable. These results indicate the lack of the stiffening, the bridge is very sensitive to the horizontal excitement. The bridge corrosion was found to have a significant impact on its capacity. Based on such findings, the load-bearing capacity of the bridge was reduced for safety reasons.