Rivet clamping force of as-built hot-riveted connections in steel bridges

Hot-riveted connections have been widely used in the past for metallic bridges, of which a large part is still in service, making relevant the assessment of their fatigue life. Previous studies have shown that the fatigue behavior of hot-riveted connections depends on many factors; among these, the residual tensile force in the rivets that clamps the plates together, i.e. the clamping force, is one of the most prone to uncertainty and scatter. Investigations p in the past made use of specimens produced in controlled laboratory conditions, potentially leading to optimistic results. This paper presents an experimental investigation on the clamping force of as-built hot-driven rivets extracted from an old steel bridge. On average, the clamping stress was found to be ∼100 MPa and ∼60 MPa, but with large scatter, for two or three plates being clamped, respectively, and for grip length over diameter ratios close to unity. This significant dependency on the number of clamped plates, as well as the lower values observed as compared to earlier studies, are attributed to larger imperfections in rivets installed in-service, as compared to the controlled laboratory environment. In addition, a finite element model is presented that simulates the development of the clamping force following the installation of the rivet. The finite element model was validated on the basis of the experimental data and it appears able to predict the effect of the grip length on the clamping force. The larger the grip length over diameter ratio, the larger is the clamping force.