| Case Name |
During the bridge beams construction, the beam fell due to losing a balance. |
| Pictograph |
|
| Date |
June 19, 1992 |
| Place |
Hourai town, Minami shitara, Aichi Prefecture. |
| Location |
The construction site of the pre-stressed concrete bridge. |
| Overview |
An upstream outside girder was hoisted and moved horizontally by a portal crane to the predefined position. When the upstream outside girder was moved upstream 1.4-meters, a beam leaned, so the girder was moved downstream 70-centimeters to put on the beam tentatively for adjustment. However, a gebinde steel bar, which hoisted the beam, bent and the beam curved upstream.
A site manager thought the gebinde steel bar would break and evacuated all workers to avoid a disaster. He tried to find an effective solution but he could not find one, so he undid a wire of the portal crane to minimize the damage. The beam was split down the middle, hit a bogie, flicked off the girder, hit a leg of the portal crane and fell to the river. No one got injured in this accident. |
| Incident |
At 14 o'clock, June 16th, 1992, at the construction site of a pre-cast T beam (the beam length: 48.454-meters, the beam weight: 175.5-tons per beam), the beam leaned about 30 degrees and curved. After undoing the wire of the portal crane, the beam was split down the middle and fell to the river, but no one got injured. |
| Sequence |
* From 8 o'clock in the morning, workers checked the machines and prepared materials. They began to move the main beam at 10 o'clock and set it on the installation beam at 12 o'clock. After that, they prepared the portal crane.
* At 14 o'clock, they started to hoist the main beam from the A2 abut side. At this time, they re-hoisted two or three times because the main beam leaned. Then, they started to hoist from the A1 abut side. They re-hoisted it several times as well and watched the main beam which was hoisted it vertically for several minutes.
* At around 14:15, they moved A2 abut side of the main beam which was 80- centimeters upstream to make the main beam parallel to the installation beam's axis and watched for 2-3 minutes.
* At around 14:30, they moved the main beam 1.4 meters to the predefined position. However, they noticed the beam began to lean so they decided to make a quick return to the installation beam. The main beam leaned 30 degrees and curved upstream before getting to the installation beam.
* At around 15:40, after undoing the wire of the portal crane, the beam was split down the middle and fell to the river with a girder. |
| Cause |
The main beam could move crosswise direction easily because the main beam was not connected to a beam hoisting device with a rigid frame structure. Generally speaking, with the T beam of the PC bridge, the crosswise direction cutting surface secondary momentum is not as strong as the lengthwise direction one. Therefore, if the length of the beam is long, the slight lean of the beam causes the huge crosswise direction deflection. |
| Response |
* Another main beam was made and installed by fixing the hoisting device on the main beam.
* A curve adjustment device was set on the main beam. |
| Countermeasures |
* The hoisting device was connected to the PC beam with a rigid frame structure.
* Holding a construction review meeting. |
| Knowledge Comment |
* When the beam was hoisted, the fulcrum should be set above the center of gravity.
* The hoisting device should have the curve adjustment structure and should be connected to the main beam with a rigid frame.
* When a long beam was hoisted, the curve adjustment measure should be taken. |
| Background |
Although the span length of the standard PC bridge design of the Ministry of Land, Infrastructure and Transport is no longer than 45 meters, in some cases, a longer span is designed. However, it is rare that the span of the PC bridge longer than 45 meters is constructed. Recently, the hoisting power becomes higher as the truck crane gets larger, so the crane construction method tends to be applied. Therefore, the opportunity to apply the beam installation method and the portal crane method is reducing, the bridge workers who have the installation skills come in lower numbers and the opportunity where the workers get the adequate skills is decreasing. In this case, an accident resulting in injury or death did not happen because there was a site manager who had enough experience. However, the site manager should have considered deeper about the curve adjustment measure and the relationship between the fulcrum and the center of gravity. Moreover, the main contractor did not manage the site adequately because the main contractor entrusted the whole work to the site manager. |
| Scenario |
| Primary Scenario
|
Insufficient Analysis or Research, Insufficient Prior Research, Regular Operation, Erroneous Operation, Failure, Deformation, Failure, Large-Scale Damage
|
|
| Physical Damage |
* One main beam
* The installation beam
* The portal crane
* The installation bogie |
| Financial Cost |
* About 50 million yen |
| Consequences |
* Quite small |
| Multimedia Files |
Fig2.A brief image of accident
|
|
Fig3.A brief image of measure
|
| Notes |
In the pre-stressed concrete bridge construction, as the method of the main beam, there are two methods, one is the pre-tensioning method which means the main beam is made in the factory, and another is the post-tensioning method which means the main beam is made at the construction site. When it is impossible to carry a beam by truck due to its long length, the pre-cast beam is made with the post-tensioning method near the construction site and carried to the installation place by the rail or the trailer. Generally, the carried beam is set to the predefined position by being hoisted and moved horizontally by the portal crane or the truck crane. In this case, the pre-cast beam was made behind the bridge abut, set on the installation beam and installed by the portal crane. |
| Field |
Civil Engineering
|
| Author |
IIDA, Tadayuki (P.S. Mitsubishi Construction Co., Ltd.)
OOTA, Yutaka (Fuji p.s Corporation)
KUNISHIMA, Masahiko (The University of Tokyo)
|
|
