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In a Japanese railroad bridge, the case was reported that the fracture occurred through the head of a suspension eyebar at the pin-and-hanger assemblies of truss bridge in 1949. After this, next some similar localized failures of hanger and pinned connections were reported. The outline of the failure cases, which were reported in those days, are shown in Table.1.
| Bridge | Structure | Failure time | Years of service | Failure location |
| Second Mogami-gawa br. | Schwedler truss | Feb. 3.1949 | 35 | Head of the diagonal eyebar at upper assemblies |
| span: 200ft | ||||
| Kurobe-gawa br. | Schwedler truss | Jul. 26.1951 | 41 | Head of the diagonal eyebar at upper assemblies |
| span: 200ft | ||||
| Arakawa br. | Platt truss | Jan. 1951 | 37 | Connection rivet hole at the intersection of the diagonal members |
| span: 150ft | ||||
| Kiso-gawa br. | Platt truss | Oct. 1.1951 | 40 | Pin center (Pin hole) at upper assemblies |
| Span: 150ft | ||||
| Fuji-gawa br. | Schwedler truss | Jun. 18.1953 | 44 | Pin center (Pin hole) at upper assemblies |
| span: 200ft | ||||
| Kono-kawa br. | Schwedler truss | Sep. 2.1963 | 55 | Head of the diagonal eyebar at lower assemblies |
| span: 200ft |
Figure.1 shows the Schwedler truss of Fuji-gawa bridge in the Toukaido line, Shizuoka. Figure.2 shows the failure pin and figure.3 shows the failure surface.
The fracture of the pin-and-hanger assemblies occurred in the head of a suspension eyebar. The fracture resulted from cyclic stress concentration unforeseen in design due to the in-plane bending of the hanger and vibration at the rail pass. Because it was reported that the hanger had thinned before fracturing due to corrosion, these hangers might have been sensitive for fatigue.
Fig.1 Schwedler truss of Fuji-gawa bridge.
Fig.2 The failure pin.
Fig.3 The failure pin.
Emergency repairs in those days were performed as follows.
1.Limit of rail pass speed.
2.Load limit of rail which passed through these bridges.
3.Insert of compressible members for the remained pair members
The example of emergency repair is shown in figure.4 ( In case of Second Mogami-gawa br. and Kurobe br. ).
As a permanent repair, new U-type members were covered over the fractured eyebars and these tips were weld connected to the original eyebars (Fig.5).These repairs were carried out in Fuji-gawa br. and so on. On the other hand, in Kiso-gawa br., the head of the fractured eyebar was replaced by a new one.
For reduced section of the pin due to rubbing activity and looser eyebar, repair that the eyebars were shortened have been performed after 1952 (Fig.6). In recent years, 1990 and 1991, this repair were carried out in Tokusawa bridge and Ichinoto-kawa bridge, Fukushima (Fig.7).
Fig.4. Emergency repair.
Fig.5. New U-type members.
Fig.6. During shortening of the eyebar by flaming.
Fig.7. During shortening of the eyebar by heating.
