Failure Knowledge Database / 100 Selected Cases

Bridge girder fell in Hiroshima "New Transportation System"
construction site
【On March 14th,1991,Hiroshima, Hiroshima】

Masahiko Kunishima・Kazutaka Matsumaru（Note）
At the Hiroshima City "New Transportation System" construction site, in the course of lowering abox-type bridge girder using the "side-loading and lowering construction method", the jack and its
mount supporting the main girder slipped out of place, allowing the girder to fall onto the prefecturalroad below. As a result, eleven motor vehicles waiting for the traffic signal to change were crushed,injuring and killing a total of twenty-three persons.
Figure 1 shows the outline of th e accident field and the "side-loading and lowering construction
method"Figure 1: The outline of the accident field and the "side-loading and lowering construction method"（source: ”Construction Accident” (Nikkei Construction) p16）

1.

EventAt around 14:05 on March 14, 1991, at the Hiroshima City elevated rail track "New transportation

System" co nstruction si te, a st eel bo x girder 63 .4 m eters l ong and wei ghing 60 t ons fel l to th eprefectural roadway bel ow. Eleve n m otor vehi cles wa iting for t he traffic signal to c hange we re1

Failure Knowledge Database / 100 Selected Cases

crushed and ten citizens died. Five workers also died. In total fifteen people died and eight people
received seri ous or sli ght injuries. It was a big disast er. Pict ure 1 is taken from the ne ar si de a nd
picture 2 is from the sky.

Picture 1:The field 1

Picture 2:The field 2（source: Picture1:”Construction Accident” (Nikkei Construction) p14 Picture2 :same p15）

2.

CourseThe jack mount had a triple tier of steel H-beams stacked in the same direction (normally each tierwould cross the previous one at a right angle). The H-beams also lacked reinforced ribs. As the result,the girder deformed since a non-reinforced section was in direc t contact with t he jacks. Two of thethree jacks supporting the main girder experienced a change of fulcrum force, and at that instant, oneof those two was loaded beyond its ability to w ithstand. As the result, the remaining jack could notsupport the reaction, so that two jacks collapsed at virtually the same instant. While executing a half
turn ar ound t he bri dge axi s, the girder fell t o th e pr efectural road bel ow, crus hing eleven motor
vehicles that were waiting for the traffic signal to change. Picture 3 shows the H-beams which lack
reinforced ribs. Figure 2 shows the situation of how the jacks fell. Figure 3 shows the process of thefalling girder.

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Failure Knowledge Database / 100 Selected Cases

Picture 3: t he H-beam s which lack reinforced ribs（ source ： ”Construction A ccident” (NikkeiConstruction) p16）

Figure 2 : The situation of how the jacks fell ( source：”Construction Accident” (Nikkei Construction)
p16）

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Failure Knowledge Database / 100 Selected Cases

Figure 3: The process of the falling girder (source：”Construction Accident” (Nikkei Construction) p17）
3. Cause
As to why the girder fell, the following is considered.
＜The direct cause＞（１） Three tiers of steel H-bea ms stacked in the sa me directi on were used as temporary jackmounts.(Fatal cause)（２） Materials where load force was concentrated were not reinforced with sheer reinforce ment
ribs, and jacks abutted sections that were not reinforced with sheer reinforcement ribs.
（３） Wires were at tached t o pre vent t he girder fro m falling duri ng sid e-loading; however, t his
countermeasure was not in place during the lowering operation.
＜The indirect cause＞（４） The supervisor had little experience of the method and was not accustomed to this work.
（５） The center of gravity of the girder was biased because the landscape was thought important.
（６） A work plan of the lowering operation was not made.

4. Immediate Action
Since the roads around the site carried traffic of 1 5,000 vehicles per day, construction was being
carried out without the total interruption of traffic; however, after the accident a detour was arranged
and the prefectural road at the erection point was totally closed to traffic, with guard rails installed tocreate an exclusive truck lane. After the accident, the Ministry of Labor (now, the Ministry of Health,4Failure Knowledge Database / 100 Selected Cases

Labour a nd Welfare) ins tituted the ac cident sp ecial investigation c ommittee. By experim ent andanalysis, the cause of the accident was investigated.
5. Countermeasure（１） Do not stack steel H-beams in the same direction for supporting loads.
（２） Install sheer reinforcement ribs on components bearing concentrated loads.
（３） Attach wires to prevent girders from falling during the lowering operation
6. Generalization
This a ccident was televised a nd the ef fect on the s ociety is not measured, wh ile the sli pshodmanagement sy stem on construc tion si tes w as expose d. That sta cking ste el H -beams in the sa me
direction is very dang erous w as tau ght. The im provement in the cons ciousness for the s afety
management in the construction field is required.
7. Knowledge（１） The "flow of t he force" of hypothesis structur e which supports heavy goods such as timber
support and frame, or the insight which perceives whether it smoothly transmits the force isnecessary for the practicing engineer in respect of the estimation method.
Figure 4 shows how the very slight slippage ((e) in the figure) causes the deformation of theestimation outside, and how tipping over and collapse are brought about.
（２） Safety is "culture". Safety is the result of daily attention to details.
（３） Not to repeat the same mistakes, the construction field should seriously consider this failure,
hand it down as a fact of the common awareness, and educate about it.

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Failure Knowledge Database / 100 Selected Cases

eFigure 4:slippage of the H-beam（Source: Author made）
8. Background
Sloppy safety management is seen as a crucial problem behind this accident. First, the selection
and oversight of th e su bcontractors w ere slop py. T he first subc ontractor ha d n ever con tracted forconstruction of ele vated str uctures, and a lthough al most h alf of t he workers o n this pro ject wer eveterans with twenty years or more experience, they had virtually no prior experience in constructionof an elevated bridge, and no advance instructions were given by the prime contractor. Among theproblems w ith t he c onstruction m anagement sy stem, no e mployees of the prim e contractor wereproviding supervision atop the brid ge pillars, and the overall supervisor was a cler ical employee ofthe firs t su bcontractor. A lso, a ccording to t he c onstruction plan prepared by t he prime con tractor,
insufficient deliberation of work procedures was carried out, and concerning the "side-loading andlowering method" there wa s merely the inscription "3(d) Side-loading" in the "Election Guidelines"of the at tached di agrams. Em ployees of t he sec ondary subcontractor that i nstalled four of t he fi vejack mounts in th is ac cident ha d m ore than t hirty y ears' experie nce as scaf folding men; how ever,they had no prior experience with the assemblage of m ounts in high places. This construction work
began on February 20, 19 91; how ever, u ntil March 1 scaf folding men scheduled to work either
arrived late, or failed to s how up a t al l on c onsecutive day s, a nd a s a result the work w as be hindschedule. After March 2, the workforce was mostly stabilized; however, many of the workers had noprior e xperience w orking in h igh p laces. A t ot her w ork sit es, i n t he m orning meeting prior tocommencement of the day's work, the day's work was reviewed and explained, and through danger
forecasting ac tivities the ke y points for danger for ecasting activities were conduc ted except for an6

Failure Knowledge Database / 100 Selected Cases

explanation of work procedures immediately prior to the side-loading of Marc h 13. Also, morning
meetings were never held.
9. Sequel
Litigation concerning indemnification to the families of the victims saw t he prime contractor, thefirst subcontractor and the owner of the construction project (Hiroshima City) admit their negligencein the Hiroshima District Court on March 24, 1998, and the court ordered payment of dam ages. In
the judges' de cision, the Hi roshima District C ourt affirmed bot h for esee a bility a nd precautionary
obligations on the part of the Hiroshima City, and awarded damages on the basis of negligence ofprecautionary ob ligations. For th e rul ing of th is Hir oshima distri ct c ourt, the Hiroshim a City
appealed as an objection. However, bereaved fa milies who des ired th e early so lution by re ceiving
the ful l am ount of t he indemnity fro m the main c ontractor company ga ve up a dem and for theHiroshima City, a nd t he a ppeal did not become the s ubstantial trial. By th e demand rej ection, it
became that the part on the Hiroshima City lost the influence in the original trial. On the other hand,in criminal pr oceedings, t he prim e co ntractor's site m anager w as sent enced t o t wo y ears a nd six
month's imprisonment, while the director of the bridge construction division and the site m anager'sassistant were given two years' imprisonment with probation of fo ur years, respectively. The prime
contractor w as ban ned fro m governm ent co ntracts as an adm inistrative p enalty, and ordered tosuspend business.
10. On the Side

After the accident occurred, the safety and health related laws were amended as a part of thecountermeasure to prevent the reoccur rence of same accident. The m ain content of t hesechanges was the addition of requirem ents that a person in char ge be appointed for dangerous
elevated erections, and advance notification be given of construction plans.
＜Reference＞“The Failure Knowledge Database” (http://shippai.jst.go.jp/fkd/Search)”Construction Accident” (Nikkei Construction, Nikkei BP)“Analysis and database construction report of failure knowledge in the 2001 fiscal year construction
field” (Failure knowledge database development project construction field research council)（Note）Department of Civil engineering, Univ. of Tokyo

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