Case Ditails

Scenario
Case Name The number of the reinforcements was drastically insufficient, and the ceiling collapsed in a V-shape under casting of concrete.
Pictograph
Date January 25, 2000
Place Hiji Town, Hayami District, Oita Prefecture
Location The box culvert construction site at the first section of improvement construction in Oita No.10 southern district in Hayami District of Oita Prefecture
Overview At the box culvert construction site at the first section of improvement construction in Oita No.10 southern district in Hayami District of Oita Prefecture, the support timber which supported the ceiling of the box culvert collapsed, and the concrete weighing about 250t under casting collapsed to the road below. There were no casualties.
Incident At about 12:30 on 25th January 2000, at the first section of improvement construction in Oita No.10 southern district, the support timber which supported the ceiling collapsed just before the completion of casting work of the concrete of the box culvert with 15.5m width and 8.3m height and 6.3m length.
Sequence * The support timbers were installed as 3 rows of 1row for each left and right along the side wall of the culvert and 1 row for the center. The number of the props in each row was 18, which brought the total to 54.
* Every three rows of timber support made up a three-layered structure which consisted of a two-tier unit 180cm high and a single layered unit 90cm high.
* It seemed highly unlikely that might happen, because the support timber consisted of 4 props and a vertical brace, a stringer, and the prop could resist a load of eight tons, and the allowable load of the basic unit was 32 tons.
* However, the number of the vertical braces was drastically insufficient. For example, the support timber installed along the side wall had only alternate the braces. Therefore, it is regarded that the allowable load of basic unit was about one-third of the design load, because the support timber did not have a brace.
* Though the H-shaped steel should have been put up over all the props and the load should have been dispersed, it was put up just alternately and the load was concentrated on the certain prop.
* As a result, the support timber which supported the ceiling of the culvert, and the concrete of about 250t, the casting of which was about to be completed.
Cause * The vertical brace was drastically insufficient. The proof strength of the basic unit was 10.3t, which was about one-third of the allowable load, because it did not have a brace.
* The effect of the slenderness ratio on the compressing force was not considered.
* Every 3 rows of timber support was three-layered structure which consisted of a two-tier unit 180cm high and a single layered unit 90cm high.
* The H-shaped steel supports were put up alternately, and the load was concentrated on the specific prop.
Countermeasures * Though every three rows of timber support made up a three-layered structure which consisted of a two-tier unit 180cm high and a single layered unit 90cm high, it should have been a five-layered structure, and the brace should have been installed on all units.
* The load should be dispersed by putting the H-shaped steel on all the props.
* The structural calculation book should be checked thoroughly.
Knowledge Comment * The planning book should be understood sufficiently.
Sequel * It is said that "the adopted timber have 500 results and this kind of timber is not particular one."
* The number of vertical braces was drastically insufficient.
Reason for Adding to DB For preventing the same kind of construction disaster from coming about.
Scenario
Primary Scenario Poor Value Perception, Poor Safety Awareness, Insufficient Analysis or Research, Insufficient Prior Research, Carelessness, Insufficient Understanding, Planning and Design, Poor Planning, Failure, Large-Scale Damage
Sources Measures for preventing a recurrence learning from 70 examples of grave accident - construction accident - , Nikkei Construction
Number of Deaths 0
Number of Injuries 0
Physical Damage unknown
Financial Cost unknown
Economic Loss unknown
Consequences Construction disaster might cause social distrust of management responsibility of original contractor, and furthermore, it might increase anxiety and distrust of danger at construction site, which the neighboring residents have.
Field Civil Engineering
Author TANAKA, Nobuyuki (Japan Engineering Consultants Co., Ltd.)
Scenario