The cause of the collapse of Hwajeong I-Park in Seo-gu, Gwangju is presumed to be the collapse of the form (gang form) and poor curing (hardening) of the concrete, and specific circumstances are emerging one after another to support this.
According to the Ministry of Land, Infrastructure and Transport on the 12th, it is estimated that the direct cause of the Gwangju collapse was that the outer wall collapsed as the 'gang form' installed during the construction of apartment houses collapsed.
On-site witnesses and experts believe that the collapse was caused by a combination of poor construction and weak structures.
At the accident site, it was identified that the rail climbing system (RCS) method was used.
RCS is an automation method (system form) that hydraulically raises the concrete pouring frame (gang form).
The system foam is installed over three floors, and the lower two floors serve to support the weight of the gangform.
This method has advantages of reducing cost and speeding up the process, but has a disadvantage in that there is a high risk of a major accident due to the heavy equipment itself.
For this reason, the Korea Occupational Safety and Health Agency specifically stipulated safety guidelines such as ▲ workers should receive prior technical skills and safety training ▲ check concrete strength before installation ▲ minimize the effects of wind.
As announced by the Ministry of Land, Infrastructure and Transport, if the collapse of the gang form was the first cause of the accident, it is analyzed that poor fixation, concrete load action, and the effect of strong winds may have acted as factors.
Also, analysis is pouring out that poor construction, such as poor curing of concrete, acted as the root cause.
In the end, the formwork collapsed while forcibly stacking the upper floors in a situation in which the concrete of the lower two floors, which supports the weight, did not dry properly in winter, and the building collapsed sequentially as a result of the impact.
In particular, if you look at the video of the accident site, you can see that the top floor of the building, from the 38th to the 23rd, collapsed like dominoes.
The apartment complex was not being built with a wall-type structure, but with a 'mushroom construction', a slab structure and a column without beams, which are horizontal structural members that support loads.
As a result, the slabs over 16 floors collapsed at once due to the impact on the top floor, and the collapse proceeded like dominoes.
The circumstances of the poor construction are also supported by eyewitness accounts of workers who participated in other construction projects at the site.
This eyewitness, who participated in the construction in the building right next to the building where the accident occurred, testified that "I didn't confirm it exactly, but it seemed that the first floor was built up every five days."
Another witness said, "The on-site manager of the process has recently changed three or four times, and most of the on-site workers are foreign workers, so there is a possibility that the work, such as tightening the formwork bolts, was not performed properly."
Regarding this, Professor Choi Myung-ki of Korea Industrial Field Professor said, "In winter, concrete does not dry well, so it has to undergo curing for about two weeks.
In addition, "If you look at the site photos taken immediately after the accident, you can confirm that the reinforcing bars remain as clean as thorns in the place where the structure collapsed. It suggests poor construction by showing the
Professor Song Chang-young of Gwangju University's Department of Architecture said, "The process is not mechanical, but man-made anchors, etc., so the skill level is important." Supervision and safety inspection should have been done properly, but there seems to be a problem.”
Professor Song said, "The fact that the collapse took place in the afternoon shows that the weight of concrete poured from the morning accumulates and affects the collapse, and the poor concrete curing overlapped and the support layer could not withstand it," said Professor Song. It is analyzed that it affected the chain collapse like dominoes.”
It was confirmed that the construction company, HDC Hyundai Development Company, received a request to supplement the safety management plan from the Seo-gu Office in Gwangju several times before the start of construction.
The Land Safety Management Agency, which received a request to review the safety management plan, repeatedly requested supplementation for the 'concrete construction' item as the contractor delayed the submission of the detailed plan on the grounds of 'not selecting a partner'.
Specifically, the Homeland Safety Management Agency instructed us to supplement the ▲ establishment of a safe construction plan and procedure for concrete construction ▲ add the safety statement of the RCS.
In particular, in relation to the RCS, which is a part related to this accident, it is necessary to take into account the loads acting on the gang form, such as total load, working load, and the load of equipment used, ▲ review the safety of supporting anchor bolts and wire ropes, ▲ review the installation strength and retention period, etc. stated that it is.
In the end, the construction company received approval for the safety management plan after requesting supplementation and reviewing it five times.
An official from the Seo-gu Office in Gwangju said, "The submission of data was delayed due to the reason that the supplier was not selected, so the review was repeated, but the safety management plan was approved without any problems before construction."
Regarding this, a construction expert said, "After the ward office has approved the safety management plan, and when the actual construction starts, it has no authority to check the site except for a safety inspection." is an issue that needs further investigation,” he said.
(Photo = Yonhap News)