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Case No.18


Support wires used in work to install pre-stressed concrete lattice girders snapped during work to assemble movable shoring



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[Circumstances of Incident]

The accident occurred during the construction of the deck of a pre-stressed concrete automobile bridge.

This construction method involved the use of a movable shoring system (hereinafter referred to as "shoring"). On the day of the accident, workers were moving the shoring forward from one pier to another, fixing them to the supports and assembling two pre-stressed concrete lattice girders into one.

In the assembly process, four cranes with a lifting capacity of 2.8 tons each are used to simultaneously lift a set of two pre-stressed concrete lattice girders. One end of each girder is hung by chains from the main girder, and the two girders are leveled and aligned to enable them to be joined together with pins and bolts to form a single supporting member.

This process was repeated as the work moved forward, and workers were carrying out work on the eighth section. Once the pre-stressed concrete lattice girders were leveled and aligned, the winching operation of the cranes was stopped and workers started final arrangements to insert the pins to make the connection.

As the victim was carrying out pin arrangement work at the center of the lattice girders, two wires supporting the girder on which he was working snapped at almost at the same time. As one end of the pre-stressed concrete lattice girder suddenly dropped, the other end still held by the chain acted as a fulcrum and flung the worker 16 meters to the ground below.
[Causes]
The following can be cited as the causes of this accident.

1 It is difficult to identify which was the first of the two supporting wires to snap. However, based on an examination of the cuts, the damage to the wires, etc., it is assumed that the wire bearing the heaviest load among the six supporting points snapped first.

2 The maximum load on the 12-mm wire that snapped is 2.73 tons, taking the hanging angle into consideration.

While the rated tensile strength is 7.24 tons when the wire is new, it was not evidently able to bear only about 2.73 tons as it was used repeatedly. It is assumed that the impact load as the victim stepped onto the pre-stressed concrete lattice girder must also be added.

3 According to an investigation after the accident, the examination of the cut wires was insufficient.
[Type of business] Bridge construction
[Type of accident] Fall
[Number of victims] One fatality
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