Case Ditails

Scenario
Case Name While disassembling bar of protecting work , a part of the protecting work was damaged, and it fell on the prefectural road.
Pictograph
Date August 22, 2001
Place Toyota City, Aichi Prefecture
Location The bridge field of the expressway which strides over the Aichi prefecture general road.
Overview In the erection field of the viaduct of the expressway which strides over the general road in Aichi prefecture, a part of the protecting work on the up-line side was damaged when the bar of protecting work which was installed in the bridge girder was disassembled and removed during the traffic regulation (the traffic stop).
Incident In August, 22, 2001 at night, while disassembling the protecting work, press volts of the vice-type clamps, which were fixing the flange under the main girder, and the square steel pipe, which held the stage planks, were broken, and the clamps came off and the protecting work collapsed. Three workers fell from the height of 10.3m with integrated stage planks and they got injured.
Sequence * Because the span between the main girders was 5m, which was long, the protecting work of this viaduct had the structure which prevented the objects from to the falling general road by setting the square steel pipe at 1.2m as a beam on the underside between flanges, by using the vice type clamps.
* In the meeting before starting work, the disassembling procedure was follows:
1. A Rafter crane and an aerial vehicle ( super deck, all movable loads of 800 kilograms )of each one to four workers were placed on the up line as a responsibility of the A group.
2. Four workers on the protecting work, one worker on the aerial vehicle and one worker on the slingling work of ground crane were stationed according to the procedure of disassembling operation.
3. The workers on protecting work removed the stage planks from near side, and it was transported, and the worker on the aerial vehicle recovered it one by one on deck.
4. The square steel pipe in the place where disassembling the scaffold was finished was removed from the aerial vehicle, after stage planks (1 row is 4m) were removed.
5. The work which is described above was done repeatedly, while it was moved at every 4m from the disassembled tip to the termination.
* Just before starting work, the workers changed the operational procedure as stated below based on the situation of the field and in respect of the work efficiency in removal work at stage planks.
1. All the four workers raised the protecting work and removed the stage planks from the termination, and they accumulated them in the tip.
2. The stage planks which were accumulated on protecting work are recovered in the deck of aerial vehicle, and they were taken by the crane to the ground.
3. After the removal of the stage planks ends, the clamps which had been installed on the square steel pipe from the aerial vehicle were loosened and removed.
* According to the schedule, traffic regulation was done from 20 o'clock , and the work was started.
* When around 20:20, when four workers were removing and transporting the stage planks from the termination and accumulating them in the tip, the clamps came off because six press volts which fixed the square steel pipe in the place where the stage planks were accumulated were damaged. The three workers of the four who were near the tip fell 10.3m to the road below with the stage planks, and got injured.
Cause * The workers selfishly changed the defined operational procedure.
* The person responsible for constructin and the work director did not notice that the workers had changed the procedure.
* Because the person responsible for construction and the work director explained the operational procedure in the meeting before the work, they thought the procedure would be carried out faithfully and neglected to confirm the work situation.
* From the overconfidence about the square steel pipe being stronger than the round steel pipe, the confirmation of the allowable load was neglected by the workers, and stage planks were accumulated on the protecting work.
* By the weight of integrated stage planks, the square steel pipe was greatly bended. The horizontal force affected the vice-type clamps. The press volts were broken and the protecting work collapsed.
Response * The protecting work in the failure division was dismantled from on the deck of aerial vehicle in order to prevent the generation of the secondary disaster, and afterwards work was stopped.
Countermeasures * The explanation of the operational procedure is done in detail by receiving workers' opinion. After the explanation, the confirmation of the understanding every single worker is done.
* The jobs of staff, the person responsible for construction responsible person, and the work director are reconfirmed, and communication and report are carried out thoroughly.
* The recovery of the stage planks is carried out from on deck of the aerial vehicle without rising to the protecting work.
* The material recovered in the deck of the aerial vehicle as under movable load ( stage planks 25 sheets ), the deck is dropped in order, and it is taken by the crane to the ground.
Knowledge Comment * Considering the plate thickness which holds the vice clamp, shape and dimension are chosen.
* Two vice clamps are used per part of material, when large bending affects the part.
Background * In the construction, the bridge became the structure that susupension metal for fitting the scaffold susupension chain was not welded. The protecting work became the structure that installed the square steel pipe by the vice- type clamps in the flange below the main girder.
* The design load of protecting work is controlled as 1 span 110 kilograms, and the limit load is not known to everybody in disassembling.
* The person in charge of concentrated on the work of traffic regulation, and left the field. He did not notice that the operational procedure was changed.
* The operational procedure which was executed efficiently was missed in the meeting, and it was insufficient to carry out the examination.
* The used vice type clamps in the position where the thickness of the bottom flange was t=53 millimeter and t=26 millimeter were the same. Especially, in the position of t=26millimeter the length of clipping the press volts was lengthened and the position became weak. There was an examination shortage.
Sequel * After the construction was restarted, a meeting was held. The simple test using the true-false test was done in order to check the understanding after the explanation of the procedure.
* The confirmation of the place where the aerial vehicles were installed was done in the daytime. The recovery of the protecting work was done from the deck of the aerial vehicle. Disassembling and removal finished efficiently.
* The same vice clamps used on the field were prepared and the replication experiment was carried out in the production manufacturer. The situations of rupture of the press volts was confirmed.
Incidental Discussion * The small number of the main girder structure emphasizes beauty and economical efficiency, and scaffold suspension metal fitting for the safety equipment has not been installed.
Reason for Adding to DB Not to repeat the same mistakes
Scenario
Primary Scenario Ignorance, Insufficient Knowledge, Organizational Problems, Poor Management, Non-Regular Action, Change, Planning and Design, Poor Planning, Failure, Fracture/Damage, Failure, Large-Scale Damage, Bodily Harm, Injury
Sources The failure knowledge database development project: construction field research council presentation material.
Hearing from the responsible person of construction company.
Number of Injuries 3
Field Civil Engineering
Author MISHINA, Takeshi (Japan Bridge Association)
KUNISHIMA, Masahiko (The University of Tokyo)
Scenario