腐食した鋼桁端部のせん断耐力評価および補修に関する研究

Abstract

Steel girders are vulnerable to corrosion due to prolonged exposure to deicing agents, humidity, and inadequate ventilation, particularly at girder ends. These regions are crucial for resisting shear forces, and corrosion can significantly reduce shear strength and load-carrying capacity. This study investigates the impact of corrosion-induced web thinning on shear strength through a numerical approach, considering several levels of corrosion damage· and the damage height. Eigenvalue analysis evaluates buckling modes and shear buckling coefficients, showing that as corrosion progresses between the web. and. lower flange, boundary conditions change, leadin to a gradual decline in buckling strength. Increasing corrosion height further accelerates reductions in both buckling and post-buckling strength. To assess more severe corrosion, a model was developed for web panels with through-thickness cracks between the web and lower flange, accounting for boundary continuity loss and its effect on shear resistance. Numerical and experimental results indicate that when corrosion affects more than half of the web's length, shear strength deteriorates significantly due to shifts in buckling modes and tension field action. Advanced corrosion patterns, such as web detachment from the lower flange, further reduce post-buckling strength by altering the tension field and plastic hinge locations. Furthermore, a study on real bridge conditions with even heavier corrosion damage reveals severe shear strength decline when both the web and lower flange sustain damage. Corrosion spreading transversely across the flange, combined with web panel deterioration, leads to web-flange disconnection, causing local yielding and a sudden reduction in post-buckling shear strength. After evaluating corrosion-induced shear strength loss, this study explores CFRP as a strengthening solution with cost-effectiveness as a main parameter. CFRP's high tensile strength and lightweight properties enhance shear buckling strength, with no notable difference between full and partial.coverage for web panels without severe localized damage. The study further identifies optimal CFRP fiber orientation for restoring post-buckling shear strength. While CFRP has been applied to repair damaged girders, this study extends the analysis to severe corrosion cases involving web detachment and lower flange damage. Results demonstrate that CFRP reinforcement effectively mitigates shear strength loss, even in extreme cases, by restoring structural capacity and preventing excessive shear deterioration when strategically applied. Overall, this study provides insights into corrosion-induced shear strength deterioration in steel girder ends, evaluating the limitations of the average web thickness approach and severe corrosion effects. Findings highlight the progressive decline in shear strength and web detachment effects while demonstrating CFRP's effectiveness in restoring shear resistance.博士（工学）http://purl.org/coar/resource_type/c_db06琉球大学University of the Ryukyu