What a plate girder is
A plate girder is a steel beam built up from plates into an I-shaped section. A thin vertical plate, the web, is joined along its top and bottom edges to horizontal plates, the flanges, producing a section that resists bending. Early examples were assembled with rivets from angle sections and plates; later ones are welded. In Japanese the term is borrowed from English, and it is also called bangeta.
Simple to design and fabricate, plate girders were used for a great many small and medium railway bridges. From the Meiji era into the early Showa period the government railway authorities issued standard designs for each span length, and girders built to them were used across the country. Designations in records such as Tatsu 540 or Tatsu 680 are understood to name these standard types.
Girders are classed by the position of the track. A deck girder carries the track on its top surface, so the girder sits hidden below it. A through girder carries the track between two girders that rise on either side. Longer spans use trusses, whose members are arranged in triangles and look quite different from the solid web of a plate girder.
Reading the records and the structure
Records for registered bridges give the number of spans and the length in the structure line, as a steel bridge of eight girder spans 139 metres long, and the commentary adds the girder type. The records for the bridges of the Wakasa Railway in Tottori describe deck steel girder bridges and note span lengths, makers and standard types. The Second Hatto River Bridge has girders of 13 and 6.7 metres made by three different firms, all of the Tatsu 540 type. The Wakasa River Bridge uses a 30-foot plate girder of the Tatsu 680 type, altered and moved from elsewhere; lengths in feet are generally taken to reflect imported designs.
Plate girders were used for more than bridges. The record for the locomotive turntable at Wakasa Station describes a turntable 15 metres across built on a deck plate girder and turned by hand.
On site, look at the girder from the side. A solid web with flanges along its edges is a plate girder; diagonal members forming triangles indicate a truss. Rows of rivets on the web and vertical stiffening plates attached to it are further signs of a plate girder.
References
- 若桜鉄道第一八東川橋梁｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00007309
- 若桜鉄道第二八東川橋梁｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00007301
- 若桜鉄道若桜川橋梁｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00007295
- 若桜鉄道若桜駅機関車転車台｜国指定文化財等データベース（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/101/00007292
Last verified: 2026.09.26