EXPERIMENTAL INVESTIGATIONS ON SLIDING FRICTION OF HISTORIC BRIDGE BEARINGS

The necessity to reassess historic bridges has yielded the recurrent insight in recent years that the bearings made from iron or steel implemented in those structures have not received any scientific attention for nearly a century. This paper presents results, some of them surprising indeed, from a series of experimental investigations performed on sliding bearings from past generation. The findings show that these types of bearings require further investigation not only for economic reasons, but also for safety issues. These examinations were to yield realistic coefficients of sliding friction. It could be demonstrated that the coeffecients at the upper margin (95%-quantile) were unexpectedly high and almost linear depending on the existing contact stress, whereas some of the coefficients at the lower margin (5%-quantile) were seen to diminish to zero, once a local maximum friction was exceeded. In addition the data measured proved that the lower coefficients do not only result from the naturally operant materials combination of the bearing parts, but furthermore are determined in differing degrees by factors such as topography of the surfaces, corrosion, dirt, contact stress and loading order. The upper coefficients mainly depend on the theoretical contact stress and the materials combined.