Full-Scale Testing and Stringer Connection Fatigue Analysis of a Historical Swiss Military Bridge for the Rhaetian Railway

Abstract

The stringer connections of a historical “Model 1936” Swiss military bridge are investigated through a full-scale field-testing program, with the aim of clarifying modeling uncertainties and enabling a standard fatigue analysis for practicing engineers. Due to global bending, axial tension forces arise in the bridge’s stringers, which were not considered in original dimensioning. In contrast to historical steel bridges with typical riveted connections, Fritz Stüssi designed the “Model 1936” military bridge with custom bolts and nuts. Unlike rivets, these custom bolts and nuts can accommodate prestressing and enhance connection stiffness and thereby encourage potential fatigue problems. Field tests with strain measurements along the stringer beams themselves were used to determine bending moment profiles and connection stiffness parameters, and to calibrate a static model of the bridge. Following the nominal stress method with a standard load model, a basic finite-element analysis indicates that the stress range in the bridge’s stringer connections lies within the prescribed fatigue limits from standards. The implementation of a five-year periodic inspection plan further ensures the bridge’s safe use and long-term integrity.