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Steel bridge on Shinkansen-railway, Japan.
The Tokaido Shinkansen is the first bullet train system in Japan. This line connects between Tokyo and Osaka 515km in length, has been carrying almost 300 trains a day since 1964.
There are totally 1511 steel bridges, about 27 km in length, in Tokaido Shinkansen.
Occurrences of fatigue damage began to be reported from around 10 years after having been put in service. Various types of fatigue cracks have been observed in many steel bridges.
The causes of fatigue cracks are categorized as follows,
1.stress concentrations due to structural details of members,
2.out of plane displacements in web plates occurring between perpendicularly crossing members such as main girders and cross beams or cross beams and stringers,
3.vibration induced out of plane distortions of web plates by high speed operation of trains.
TIG dressing have been applied as a retrofitting method to fatigue cracks of type 2 and type 3, and also as a prevention works to suspicious details. The applied details are the ends of vertical stiffener (Fig.1), the connections between longitudinal ribs and diaphragms in box girder, and the ends of gusset plate on web.Fig.1
Deck or through type girders, trusses.
Fluctuating loads due to Shinkansen trains traffic.
The standard conditions of TIG dressing under flat position are as follows,
electrode: Tungsten, 3.2mm in diameter
current and voltage: 240A, 13-14V
speed: 45-60s/100mm
These conditions are also applicable to works under other positions. A little lower current is recommendable for horizontal, vertical and overhead positions.
After TIG dressing works, the configuration and size of bead is examined as shown in (Fig.3),
TIG dressing works were performed at totally, 18111 details in steel bridges in 1962. the conditions of these details have been observing periodically and no recurrence of fatigue crack until now.
| area | execution | inspection | ||||||
| number of bridges | number of girders | number of details | number of bridges | number of girders | number of details | inspection ratio | recurrence | |
| Tokyo | 3 | 73 | 8486 | 1 | 1 | 38 | 0.4% | 0 |
| Shizuoka | 10 | 92 | 4109 | 10 | 67 | 3279 | 80% | 0 |
| Nagoya | 12 | 94 | 3026 | 2 | 4 | 160 | 5% | 0 |
| Osaka | 8 | 64 | 2490 | 1 | 2 | 68 | 3% | 0 |
| Total | 38 | 323 | 18111 | 14 | 77 | 3545 | 20% | 0 |
