Case Ditails

Scenario
Case Name The rod of the suspension metal fitting broke and the PC girder fell down.
Pictograph
Date November 17, 2000
Place Odate City, Akita Prefecture.
Location The bridge building construction site.
Overview In building the PC (prestressed concrete) girder, a rod of a suspension metal fitting broke and the PC girder and installation girder fell down into the river.
Incident In the building of the post-tensioning hollow grinder bridge, the 5 of the 6 main grinders had been built, and the last grinder was lifted by 2 truck cranes, and moved to the side. Then, suddenly the rod of the suspension metal fitting broke and the PC girder and installation girder fell down into the river.
Sequence * During the work of the building the post-tensioning hollow girder bridge, there was the work to set up and build the PC girder (L=40m, W=103t) on the erection girder.
* The five of the six main girders had already been built. The workers finished building the last girder and moved it to the side, lifting it by two truck cranes. Then, the rod of the suspension metal fitting of the bridge side, and the PC girder fell down on the PC girder which had already built.
* After that, the rod of the suspension metal fitting of the opposite side broke and the PC girder completely fell down on the PC girder which had already been built.
* The leaning PC girder fell down and crushed the installation girder. It fell down into the river with the erection girder.
* The PC girder fell and broke. The erection girder got damaged and deformed.
Cause * Workers had cut and connected around the rod by welding to convert it. But, at that time, they cut a part of the rod by welding and the calculated strength became weak.
* They tried to weld the cut part, but the welding wasn't accurate. So, there was a cavity in the rod and the design strength became weak.
* Because the converted part was painted, in the visual inspection, they couldn't discover the conversion in both inspections, the equipment management section and the construction site.
* It was used without knowing the fact of the conversion, in the site.
Response * They investigated the substructure and the PC girder had already been built, and confirmed the solidness.
* The PC girder which fell down was discarded. They made a new PC girder.
* They investigated the cause of the accident, and made a new suspension metal fitting and resumed the building.
Countermeasures * The suspension metal fitting of all companies was investigated and checked. The things ,without any plan and which origin was unknown ,were put into the discard.
* As a countermeasure of recurrence prevention, they made and operate the standard for management and check systems.
Knowledge Comment * Don't convert any machinery and materials! If they want to convert something, they need the ground (the calculation of the strength) !
* They have to be thorough in the management.
Background * The suspension metal fitting was made and used in 1979, and afterwards, it used in 2 construction sites.
* It was converted in either site of the 2 construction sites. When it was cut and welded, a part of the rod seemed to be cut.
* The cut part had been repaired, but the rod was used in `SMC use', and the weld was not adequate for the materials.
* The welded part had been painted, so the conversion couldn't be discovered in the observation inspection of the machinery and materials management division.
* The history management was insufficient, and the record of their uses were not correct.
Reason for Adding to DB Not to repeat the similar failures.
Scenario
Primary Scenario Organizational Problems, Poor Management, Insufficient Analysis or Research, Insufficient Prior Research, Ignorance, Insufficient Knowledge, Planning and Design, Design Misuse, Usage, Maintenance/Repair, Failure, Fracture/Damage
Physical Damage The breakage of the PC girder and the building girder.
Field Civil Engineering
Author ITO, Katsuhito (P.S. Mitsubishi Construction Co., Ltd.)
Scenario