Takuya Kobayashi 

Study on the Buckling Strength of I-Girders Subjected to Negative Bending with Corrosion-Induced Section Loss in the Bottom Flange

Eiji Iwasaki 

 Many of Japan's bridge infrastructures were constructed intensively during the period of rapid economic growth, and a large number of these bridges have now been in service for several decades. As a result, the proportion of aging bridges has been steadily increasing, and the deterioration of structural performance and durability has become a serious concern. Meanwhile, it is unrealistic to maintain all bridges at a uniformly high standard. Therefore, in order to allocate limited resources efficiently and rationally, it is essential to establish maintenance priorities.
Accordingly, this study focused on the local buckling strength of the bottom flange near the intermediate support of steel I-girder bridges, and aimed to quantitatively evaluate the local buckling stress when corrosion-induced thickness reduction progresses. In particular, since the bottom flange is subjected to compressive stress under negative bending moments in the intermediate support region, It is important to clarify the influence of corrosion-induced section loss on the reduction of local buckling stress.
 Elastic plastic analyses were conducted using a finite element method (FEM) analysis program, and multiple analytical cases were examined in which the degree of corrosion-induced thickness reduction was varied stepwise. Furthermore, based on the obtained analytical results, detailed investigations were carried out regarding the influence of corrosion-induced thickness reduction on local buckling stress. The reduction trend of buckling stress due to differences in corrosion level and the characteristics of its variation were systematically organized, and their relationship with local buckling strength was clarified.
 Based on these findings, an evaluation formula representing local buckling stress was assumed, and regression analysis was performed using the analytical results. As a result, a new evaluation formula capable of relatively simple estimation of the local buckling stress of the bottom flange near the intermediate support of corroded steel I-girder bridges was proposed.