written in front: is to clarify the causes and consequences of the accident, the article is longer, and has an understanding of the accident To see the official, you can swipe down directly to see the summary part.
In just 20 seconds, nearly 1,500 people were crushed under 42,000 tons of rubble. This was the collapse of the Sampoong Department Store in 1995, and it was also the largest casualty accident in South Korea during peacetime. The collapse caused 502 deaths, 937 injuries and economic losses of 66.7 billion won.
The Mitutoyo Department Store built by the South Korean Mitutoyo Group is located in a prime location in Seoul and has more than 1,000 employees. The consumers are office workers in the capital. This luxury department store has five floors above ground and four floors underground. It receives an average of 40,000 customers per day and has a weekly turnover of 4 million US dollars. The disaster happened when the department store opened its fifth anniversary. So how did such a tragic accident happen?
has been noticed in advance
Department store at 8 o'clock in the morning on June 29, 1995 Facilities manager Li Yongzhou noticed that there was a note left by the night guard on the table, which mentioned the strange noise from the roof last night.
Because Sanfeng Department Store just passed the regular security check, he didn't care about it either.
Crack in the ceiling
Two hours later, Chun Yuan Restaurant on the fifth floor of the mall contacted Li Yongzhou.
They found that a huge crack appeared around a pillar in the restaurant, the width of which can be inserted into a fist.
Li Yongzhou decided to temporarily close the restaurant and asked the staff to remain silent to avoid panic.
The day before the collapse, the sloping restaurant floor
also felt that customers who were not shopping in the department store were also in the department store. shock.
After receiving customer feedback, Li Yongzhou thought it might be caused by air conditioners.
So at 12:30 noon, he turned off the air-conditioning in the building.
At the same time, Mitutoyo Department Store broadcasted the news of the air conditioner failure to customers and employees.
After assessing the risk, refused to close the business for repair
in the afternoon. Chief Li Di called the supervisors to discuss countermeasures for cracks and vibrations in the building.
They invited Li Hezhu, a structural engineer in charge of building the building, to check the cracks.
Li Hezhu found that the cracks had spread to the roof of the entire building, and small collapses appeared in some areas.
After carefully assessing the risks, Li Hezhu believed that the building should be closed immediately and urgently repaired.
But his proposal was quickly rejected because the management did not want to lose the considerable turnover that day.
What they don't know is that this decision will lead to more dire consequences.
In the evening, the crowds off work poured into the Sanfeng Department Store, which is the peak of the day.
Bustling customers crowded the counters of the department store.
At 5:40, a rumbling noise came from the roof of the building.
More than 1,500 people in the Sanfeng Department Store have not realized that the building is on the verge of collapse.
Seven minutes later, a louder cracking sound came from the roof.
The floor slab of Chunyuan Restaurant on the fifth floor is penetrated by pillars, so it is unable to bear more weight.
The extra load is shared by the other columns, but obviously it will not last long.
At 5:52, the alarm bell in the building finally collapsed.
People rushed towards the exit amidst alarm and roar, but everything happened too fast.
In less than 20 seconds, each floor continuously collapsed and hit the ground heavily, raising a lot of smoke and dust.
A total of five layers of debris were pressed on top of the four underground floors, and the number of people buried could not be estimated.
Due to fear that the heavy bulldozer might hurt the buried person, rescuers could only remove the gravel with their bare hands.
Some large cranes also arrived at the site and began to carefully lift the wreckage.
By the early morning of the next day, a total of more than 200 survivors were rescued, but the death toll was also rising.
In addition to rescuers, there are accident investigators busy at the disaster site.
They are eager to know what caused the collapse of the Sanfeng Department Store, which was built only 6 years ago.
This may be related to the safety of high-rise buildings in Seoul or even across the country.
After excluding the possibility of earthquakes and terrorist attacks, investigators suspected that there was a problem with the foundation strength of the building.
The original site of Sanfeng Department Store was a landfill, and its weak soil layer probably caused the collapse.
But the survey showed that the basic location of the building is accurate, and there is no problem with its strength.
The investigators began to focus on the building itself.
They collected about 150 sets of concrete samples from the rubble pile and tested their strength in the laboratory.
Unexpectedly, the concrete strength of the building also reached the standard.
The accident investigation was once deadlocked.
Concrete compressive strength test
The investigator who lost his mind decided to sort out the information at hand.
When calculating the building's architectural drawings and bearing capacity, they found some clues.
According to calculations, the building needs 80cm-diameter columns and 16 steel reinforcements.
The on-site measurement shows that the diameter of the column has been reduced to 60cm, and there are only 8 steel bars.
This has reduced the overall strength of the building by nearly half.
But this is not the main reason for the collapse of the Sanfeng Department Store.
The building is designed with safety reserves, that is, the bearing capacity required by the design is greater than the actual bearing capacity required.
Even if the strength is greatly reduced, the building can still remain intact under no special circumstances.
This is also the reason why there has been no major problem in the 6 years since the building was built.
As the investigation deepened, the investigators discovered another construction defect on the spot.
This time, the steel bars in the concrete floor are misplaced, from 5cm from the surface to 10cm from the surface.
These five-centimeter changes are not trivial, which is equivalent to directly weakening the thickness of the floor.
The Sanfeng Department Store adopts a beamless floor structure*, and only the floor and columns bear the load.
This error reduced the strength of the floor slab by 20%.
*Note: There is no beam under the floor, and it is directly supported by pillars. The instability of a column can easily lead to building chain damage, and the requirements for design and construction are quite high.
Various signs indicate that the Mitutoyo Group’s management had major negligence, and they were all negligent when the disaster occurred. All survived.
So the investigators turned their attention to them.
Mitutoyo Group President Li Wei (first from the right)
was initially in the design process. The building has only four floors and is intended to be used as an office building.
After the original contractor completed the foundation, Mitutoyo Group put forward a request for substantial design changes.
They not only changed the office building to a shopping mall, but also added an extra layer on it.
This change resulted in the cancellation of many load-bearing columns to make room for the installation of escalators.
The contractor did not agree to the amendment, and the chairman Li Li simply fired them and let his construction company take over the construction.
Li Yongzhou also revealed that the fifth floor of the mall was originally intended to be an ice skating rink, but it was later changed into 8 traditional ice rinks. restaurant.
Koreans have the habit of sitting on the floor, so heating equipment must be installed under the floors of all restaurants.
Additional equipment adds a fifth floorThe weight of the board puts a lot of pressure on the structure of the originally four-story building.
Another culprit of the building’s serious overload is the air conditioning equipment on the roof.
The total weight of the three large water-cooled air conditioners is 29 tons, which can reach 87 tons after being filled with water, which greatly exceeds the design standard.
After investigation, the most critical factor in the accident also came from these three air conditioners.
Two years before the disaster, three air-conditioners were moved due to complaints from nearby residents about the noise of air conditioners.
This kind of large equipment was supposed to be hoisted to a new location with a crane, but Mitutoyo lazily placed the air conditioners on the wheels and dragged them directly on the roof.
It turns out that this is a very bad decision.
Tens of tons of air-conditioners were dragged to the other side of the roof, causing irreversible damage to the building structure.
There were cracks of varying degrees in the places where the air conditioner passed. Among them, the pillars of the Chunyuan restaurant were particularly damaged.
In the past two years, cracks will spread every time the vibration caused by the air conditioner is turned on.
When there are enough cracks around the pillars, the floor slab of Chunyuan Restaurant can no longer bear it.
After the first floor slab fell, the collapse quickly spread to the entire floor.
The upper floor slab fell to the lower floor, causing the lower floor to collapse, and Sanfeng Department Store was razed to the ground.
502 lives were taken by this disaster, people can’t understand how such a random project passed the audit .
Follow-up investigation revealed that several government officials were suspected of being involved in the construction of Sanfeng Department Store In accepting bribes, there are also widespread corruption and frauds within the Mitutoyo Group.
From the engineering point of view, why is such a beautiful building collapsed?
1
Change of purpose, dismissal of contractor
Mitutoyo Department Store was built by the Mitutoyo Group and is located in the prime location of the sub-center of Seoul today and South Korea today Next to the accounting school building. In 1987, the group started to build a department store on this open land in Seocho District, which was originally used as a landfill. According to the original design, the building will be built into a 4-story office building, but Mitutoyo Group Chairman Li Di was redesigned into a department store building during the construction project. This change resulted in the cancellation of many load-bearing columns to make room for the installation of escalators. The original construction contractor refused to continue construction according to the new design. Li Yao fired them and let his construction company carry out the construction. This kind of random modification of the building's load-bearing columns planted the seeds for the collapse of the building.
2
SetAccording to the survey, it is found that according to the calculation result of the safety standard of the building, the diameter of the column of the same cross-section used in the Sanfeng Department Store should be 80cm, and the diameter of the column in the construction drawing should be 80cm. The marked column cross-section size is 60cm, and the actual measurement result on site is also 60cm. This kind of seemingly small mistake is the biggest hidden danger.
3
Cut corners to halve the column reinforcement, which reduces the bearing capacity of the column by nearly half.
The investigators also found that the reinforcement in the middle of the column is also Reduced from 16 of the construction icons to 8 . The reduction in the cross-sectional dimensions of the columns and the halving of the number of steel bars reduced the load-bearing capacity of the columns that bear the load of the entire building by nearly half. Seeing the editor here is sweating in my heart, I am really afraid that the house above my head will collapse in the next second. This kind of cutting corners is simply a disguised attempt to harm others' lives!
4
The position deviation of the force-bearing steel bar of the floor slab reduces the load-bearing capacity of the floor
After actual measurement, is the force-bearing bar in the concrete floor According to the requirements, it should be 5cm away from the ground, but the actual difference is as much as 10cm. This is equivalent to thinning the thickness of the floor slab, which also leads to a 20% reduction in the strength of the floor at the connection with the columns. Although these two changes cannot directly lead to the collapse of the building, they provide a shortcut for the collapse.
5
Increase the fifth floor and change its use
During the construction process, the decision makers of Mitutoyo Group proposed The original design of the four-story building is added to the fifth floor , and its load is added to the building. The original plan was to use the fifth floor as an ice skating rink, but the management changed its use midway and replaced it with eight Korean and Korean gourmet restaurants. Because Koreans have the habit of sitting on the floor when eating, a layer of heating equipment is added under the concrete floor of these restaurants, which in turn increases the load of the load-bearing structure. This high burden brought a heavy blow to the already precarious building.
6
Mobile air conditioner
The air conditioning equipment (water-cooled air conditioner) of the whole building is now installed on the roof. on. 3 large air conditioners weighing 29 metric tons, and when the air conditioner is filled with water, the total weight is up to 87 metric tons, which is 4 times the design standard load.
To make the situation worse, in 1993, all the air-conditioners at the rear of the building were moved to the front due to complaints from surrounding residents about the noise of air-conditioners. Cranes were supposed to be used for this movement, but the result was that all the equipment was pushed into place by pulleys directly on the roof, causing great damage to the entire roof structure and cracks in the air conditioner’s reach. The vibration caused by the operation of the upper air-conditioner caused cracks in the connection point between the No. 5E pillar and the roof of the air-conditioner, and the pillar could not perform its function.
Conclusion
Commercial groups pursue their own profits, while government officials turn a blind eye to the chaos of the project. Even when the crisis is on the verge, the dizzy capitalists are still greedy for half a day of profit, at the risk of betting on the safety of more than a thousand people. The result of the accident is distressing, but the reflection on the accident is even more alarming. Safety is no small matter, and engineers must always keep in mind: the blind pursuit of interests is the best hotbed of disaster!
Statement : The article comes from the SME science and technology story, created in the middle, and organized by the comprehensive editor of construction technology. Content copyrightBelongs to the original author, please contact to delete if there is any infringement.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-