Riku KABASAWA

Study on Stress Evaluation of Gusset Section Just Above the Lower String of a Truss Bridge with Corrosion Thinning

Eiji IWASAKI

Steel truss bridges are known to have low redundancy. In particular, gusset plates play a crucial role in connecting multiple members, making them highly susceptible to structural impacts caused by damage due to corrosion or fatigue. Additionally, nodal points tend to accumulate rainwater and dust, leading to localized corrosion. While design specifications provide the required plate thickness for gusset plates in truss bridge nodes, there are no established criteria for assessing damage that occurs after construction. Furthermore, the stress state in these areas is complex, requiring finite element analysis for evaluation, which is time-consuming. As a result, making prompt decisions regarding the necessity of repairs remains challenging.To address this issue, Iwasaki et al. proposed a simplified method for evaluating the stress state at these locations based on equilibrium conditions and several assumptions. However, their method focused on nodal points in Warren-type steel truss bridges, without considering Pratt-type trusses, which are more widely used. Unlike Warren-type nodes, where diagonal members are inserted symmetrically from both sides, Pratt-type nodes have diagonal members inserted from only one side, making it impossible to ignore axial forces in the vertical members. Consequently, stress evaluation formulas developed for Warren-type nodes may not be applicable to Pratt-type nodes.In this study, we examine a simplified method for evaluating the stress distribution directly above the lower chord of the gusset in Pratt-type steel truss bridges.

As a result of the study, we proposed a stress evaluation formula that allows calculating the stress distribution directly above the lower chord of the gusset in a Pratt-type steel truss bridge without relying on finite element analysis. Additionally, several parameters were introduced to compute the stress distribution. These parameters were determined as constants or based on the nodal geometry, such as the insertion depth and angle of the diagonal members, through comparison between the evaluation formula and FEA results.