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A balloon flange girder is a form of vertical I-beam wrought iron plate girder, where the top flange, instead of being a simple flat plate, is extended into a hollow tube. This type of girder was rarely used, its only common user being Isambard Kingdom Brunel in the 1840s and 1850s. == Design == Brunel was working at a period of increased theoretical and mathematical analysis of bridge and mechanical structures. Together with the work of Charles Fairbairn, particularly in relation to Stephenson's tubular bridges such as Conwy, there was an increased understanding of how beams in compression would fail by buckling. Brunel was known for his distrust of cast iron as a material, at least for large beams. This distrust of cast iron was vindicated when his friend Stephenson's adventurous cast-iron Dee Bridge (1846) collapsed in 1847. Brunel gave evidence in his support at the following inquiry, but this was on the basis of Stephenson being a competent engineer within the bounds of current knowledge, rather than in support of large cast-iron beams.〔 Stephenson's Dee Bridge had used a truss girder, where an inverted T-shaped cast iron girder was trussed by applied wrought iron tension bars. This faulty design was instrumental in the bridge failure, where tension in the truss rods increased compression in the upper part of the girder such that it underwent columnar failure. Despite this, although with the advantage of hindsight, Brunel would use similar applied tension chains for his truss design. Around the 1840s, developments in the puddling furnace reduced the cost of wrought iron and improvements to rolling mills allowed the production of large flat sections. This iron was now economic for the construction of girders, assembled by riveting of flat sections. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Balloon flange girder」の詳細全文を読む スポンサード リンク
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