Two new measurement methods for rivet clamping forces of as-built hot-riveted connections

Hot-riveted connections have been widely used in the past for steel bridges which are still in good condition and in operation today. Due to conservative predictions of the remaining fatigue life, based on S-N curves, unfortunately these historical structures are often replaced too early. This should be prevented due to reasons of climate change and sustainability. Previous studies already showed a high potential of alternative prediction methods, based on fracture mechanics, to increase the remaining fatigue life significantly, especially if the beneficial effect of clamping forces of the rivets is considered. This requires an improved fracture mechanics model on the one hand, and the knowledge of the clamping forces, in term of their magnitude and scatter, on the other hand. Within a research project two new methods were developed, either destructive or non-destructive, for the accurate measurement of the clamping stresses in rivets. These methods are also applicable for small grip lengths. Within this paper, the theoretical background and the application of these two new methods are presented in detail. Further, also the results and a statistical evaluation of the measured clamping stresses from a first measurement campaign at a representative railway bridge – with a high sample size of investigated rivets – are shown. Finally, also the effects of the rivet misalignment (eccentricity of rivet heads) on the clamping stresses are discussed. • Two new methods were developed for measuring the clamping force in hot-driven rivets. • The new destructive method has some benefits compared to cylindrical strain gauges. • The new non-distructive method is also applicable for in-situ measurements. • The clamping force of n = 30 rivets from a railway bridge has been measured. • The correlation between rivet imperfections and clamping force has been analyzed.