Case Ditails

Scenario
Case Name Steel truss girder of 77.1m length and 210t weight under erection falls 40m in the valley.
Pictograph
Date August 10, 1997
Place The Hokkaido Shizunai District Shizunai town.
Location Bridge construction site of general road Shizunai and Nakasatsunai line.
Overview * In a bridge construction site of general road Shizunai and Nakasatsunai line, the truss girder under erection fell 40m. This bridge was 141m in length and it was composed of simple I girder of both sides span and simple truss girder of the center span, and the simple truss girder was installed by the cable crane direct suspension method.
* The setback of the steel tower top was carried out by an adjusting device equipped as a prior intervention in buck stay cable (56φ ) in order to install and close the last member ( upper chord material of the truss central ) of the truss girder. On the day of the accident, however, the truss girder which was suspended fell 40m in the valley because the main cable slipped at wire clip division which was fixed in the steel tower top.
Incident * Around 16:45 on August 10th, 1997, the truss girder (77.1m length, 210t weight) fell during installation. Four workers who was doing another work on. The girder fell with the girder and one worker died, and three workers received serious or slight injuries.
Sequence * The installing and closing the last member of the truss girder would be done within the same day, and the workers would have the summer vacation(the Bon Festival ) from the next day.
* It was proven that the space was narrow when the mounting division of the last member was measured before the installation work. Therefore, the workers intended to lift the suspended truss girder and extend the closed space of the center of the upper chord material by tilting and adjusting ( setback ) the steel tower outside.
* The steel tower of A1 was tilted by fixing 350 millimeters during the morning. In the afternoon, the equipment was transferred. When the steel tower of A2 side was tilted by 20 millimeters per fixed 250 millimeters, the wire clip stops of the downstream main cable (12 wire clips were used at the top of the steel tower) slipped and the suspended truss girder fell 40m in the valley, rotating downstream.
* At that time four workers who restored the handrail near the P2 bridge pier fell with the truss girder.
Cause The direct cause was that the main cable slipped in the wire-clip division under the setback work.
* The wire clip stationary portion of the main cable was at the top of the steel tower. It was tightened in the erection middle point, but tightening work was insufficient because the tightening was done in a bad scaffold.
* The reason the workers were involved was because they were doing the different work on adjusting girder simultaneously.
Response All one's energies were directed to rescue victims and inspect the site, and first-aid measure so a secondary accident could be prevented.
Countermeasures The following facts were considered while the truss girder was manufactured again and after the half year installed similarly by the cable crane direct suspension method.
* The engineers who were well-informed about the method were increased by eleven persons, and the workers were also changed for the ones who had experienced the method.
* Clip stops of the steel tower top of the main cable were changed for the socket stops.
* The number of the clip of the buck stay was increased from 11 to 15 per 1 place.
* The direct suspension hanger was changed to chan block ( the 20t suspension ) from the turnbuckle, and the adjustment became easy to be done.
* The counter weight was loaded in the erection middle point, and the rotation on the supporting point would be suppressed.
* Before the accident, it was installed in the direct support. In re-installing, the temporary key which made the vertical rotation possible was produced and used.
Knowledge Comment * Since the cable stretches with the increase of the tension and the cross section of the cable also changes, it is important to carry out tightening of the wire clips carefully with the progress of the erection.
* The engineer is present in tightening, and he or she confirms it directly.
* The adjustment in the erection is not concentrated toward the end of the process, but is carried out in the suitable and regular time from the early stage .
Background Supervision engineers of the subcontractor company had much experience of the cable crane, and constructed with self-confidence, but it is clear that they were careless.
* The workers had little experience of the method, and they only obeyed the supervision.
* All the workers stayed in the lodging house. Because the Bon Festival vacation began from the next day, they were impatient to finish the closing work of the truss.
* The confirmation of tightening the wire clips was carried out with riding gondola in the overhead division ( 30m from ground), and it was lacking in certainty.
Sequel * Four workers fell with the girder. Two workers who stopped in the slope in the valley suffered the slight injury. One worker from the other two who fell to the bottom received the serious wound. The other one worker were flown by the incleased mountain stream and became missing. As a result of searching by the investigation fleet day after day, his remaina were discovered after about one month.
* All energies were directed to consult about the compensation for the bereaved family and report to the concerned government office concerned.
* Though the production company which made the girder was different from the one which fabricated on the site, it was possible to construct it by the same method after immediately requesting it from the production company.
Incidental Discussion * Removing the fallen bridge girder and cleaning up were delayed because a big crane could not approach the field.
* After the fallen girder was removed, the main cable was stretched again, and the scaffold was also repaired, and the erection was made to finish in the perfect system.
Account of Concerned Parties * The subcontractor company experienced the bridge erection of this scale many times and had the self-confidence for the construction. The charge branch also had no disaster at that time and thought carelessly.
* In order to attempt strengthening of the safety management after the accident, the safety technique section was set up in the conventional safe headquarters. And following the prior check of construction scheme, the construction confirmation on the spot and technical hearing became necessary.
Reason for Adding to DB As a lesson, it is the largest shame for the bridge company to let the bridge girder fall under erection !.
Scenario
Primary Scenario Poor Concept, Poor Strategy or Concept, Organizational Problems, Poor Staff, Production, Hardware Production, Malfunction, Specifications Not Met, Failure, Large-Scale Damage, Bodily Harm, Harm to Physical Well-being, Bodily Harm, Death, Loss to Organization, Social Loss
Sources Nikkei construction edition "recurrence prevention measure studying construction accident, significant 70 examples".
The failure knowledge database development project: construction field research council presentation material.
Number of Deaths 1
Number of Injuries 3
Consequences Information of the accident is reported by newspaper and television, and the social responsibility of the bridge company which lost the confidence about the bridge erection technology is big.
Field Civil Engineering
Author SHIBAHARA, Hidemasa (Japan Bridge Association)
KUNISHIMA, Masahiko (The University of Tokyo)
Scenario