| Case Name |
The gate construction overturns by the horizontal force through the suspender wire. |
| Pictograph |
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| Date |
December 1987 |
| Overview |
In the PC (prestressed concrete) superstructure construction, when PC girder was suspended by portal suspend device (gate type construction) and moved horizontally to installation position, the horizontal force affected to the device in lateral motion through digit suspoension chain, and fixation anchor of guy wire was drawn, the gate construction overturned and the girder fell.
Mercifully no one was injured in this accident. |
| Incident |
In November, 1987 during PC superstructure construction, since a digit suspension equipment (gate type construction) overturned, the PC girder of 40m length and 100t weight fell on the road under the bridge,
but mercifully no one was injured in this accident. |
| Sequence |
It was a drawbridge in which angle of pier and abutment differed from the left and right sides this bridge( P1 angle of skew 95° 12', A2 angle of skew 84° 47' ).
The erection digit ( the election girder )was installedin. He bridge center, and extraction work was carried out on the erection digit in respect of the PC girder outside of the drawbridge.
When PC girder was suspended by portal suspend device (gate type construction) and moved horizontally to about 60m in the P1 side and 1m in the A2 side from laterally for installation position, the horizontal force affected to the device in lateral motion through digit suspoension chain, and fixation anchor ( concrete block : Weight 5.5t ) of guy wire was drawn, the gate construction overturned and the girder fell.
The PC girder fell on the road under bridge, and mercifully no one was injured in this accident. |
| Cause |
The erection method in which direct horizontal force affected the digit suspension apparatus ( the gate is constructed ) was adopted.
Because of the PC girder arrangement was a plectrum shape, the span changed between when the PC girder on the erection digit was suspended and moved horizontally to fixed position, and the change affedted the guy anchor of the gate construction as a horizontal force.
In the office construction review meeting, the quality of the erection method was not judged, they expected in staffs who had experience technology of field, and appropriate change indication wasn't done.
Since the draw angle was small, it was judged that it was sufficient to consider only horizontal force.
Since the position of the concrete block of guy anchor was changed, the safety factor ( over 1.5 for sliding ) was not satisfied.
It had been considered extra (25%) horizontal force by some impact, but the real impact ( length deflection, width deflection ) was bigger than assmed.
The confirmation of work sharing and the system were imperfect. |
| Response |
The PC girder was took apart and away at once.
A reconstruction work procedure instruction sheet was made and reconsidered.
Clear up the system and parts construction work manager and workers.
The construction method of PC girder was remade, and in the office construction review the construction method of most sefety pallarel girder method was discussed, but it was difficult to supply a construction girder, and they had no choice but to adopt the construction method of a single girder as originally planned.
Considering prescribed safety factor ( it is two times than usual for horiztal force of suspended load ) for tension force of guy anchor, in addition, the safety was confirmed by doing a suspension test to check that it hangs it on the erection digit and that the largest horizontal force affects the equipment ( the slight clearance in weight car truck for the length transfer and PC girder underside is taken ) . |
| Countermeasures |
Adopt the erection method which the load except for the horizontal force allowed for the gate construction guy wire by safety regulation and cranes structural code such as the crane does not affect.
1. ( Construction of erection digit + Transportable crane ) The PC girder is drawn on the erection digit, and it is hung and is constructed by the transportable crane installed in both sides in the phase. This method becomes possible a case in which the transportable crane can freely advance to the erection site.
2. ( Construction of digit erection + Support digit ) The steel support digit ( the nose type shape style member) that it lifts to both sides of PC girder and resists the load is installed so that the span may not change in lift, in the traverse motion. The horizontal force does not work, because that the gate is constructed this time is parallelly installed regardless of the bridge shape.
3. ( Construction the 2 set erection digit erection + traverse motion frame facility ) Erection digit of the 2 sets is installed for usurpation equipment of the on steel installed at the erection span. The digit suspension equipment facility ( the bipartite style ) done the selfpropellent on the erection digit of the 2 sets is assembled. The PC girder drawn on the orbit by the cash drawer facility is held in erection digit of the 2 sets, and it is transported to the fixed position. The PC girder is installed on the steel frame of both sides in the condition that it was held in the erection digit in usurpation and fixed position. The thorough discussion was not made in the office construction review meeting.
And, it is necessary to clarify ideal way, organization, role of office construction review meeting, because the recognition of being the special erection was lacking.
To change the position of the guy anchor in the construction is that action horizontal force also increases by the angular variation of the guy, and the thoughtless change from the construction experience is not absolutely carried out. |
| Knowledge Comment |
By investigating the environmental condition of the erection position, because there are many cases that road, railway, crossings such as the river are planned from abutment and bridge pier arrangement conditions in the draw-type bridge, and because there are many cases in which the erection work is restricted and approach of the self-propelled crane to the cross-link site is limited, the erection plan is made. When the draw-type bridge is constructed by the erection digit erection method, it is the principle that the load except for the horizontal force allowed by crane safety regulation and crane structural code does not affect in the digit suspension equipment guy anchor, and it must be avoided that horizontal force by the suspend load is generated by the construction technique. The plan to the plan while working should not be carried out. The construction review meeting is carried out, when change if unavoidably changes, and it confirms safeness. The safety of the work is not secured only by the erection experience technology. |
| Background |
There are many results on erection digit construction of the PC girder as a general erection method. And, erection digit erection of the draw type bridge has also been safely constructed by ( the erection digit erection + support digit ) methods or ( the 2 set erection digit construction + traverse motion frame facility ) methods, etc.. In the case of this bridge, it seemed to connect the result of depending on that it thoughtlessly carried out the work without also relating to recognizing that horizontal force works in the stage of the erection plan, since the draw angle was small, experience technology such as the plan change on the spot and with the accident. |
| Reason for Adding to DB |
To avoid repeating the same mistakes. |
| Scenario |
| Primary Scenario
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Misjudgment, Misjudgment of Situation, Insufficient Analysis or Research, Insufficient Prior Research, Organizational Problems, Poor Management, Regular Operation, Erroneous Operation, Regular Operation, Erroneous Operation, Failure, Large-Scale Damage
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| Number of Deaths |
0 |
| Number of Injuries |
0 |
| Field |
Civil Engineering
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| Author |
TANAKA, Miyo (Japan Prestressed Comcrete Constructors Association)
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