On June 29, 1995, the Sampoong Department Store in Seoul, South Korea which had four basement floors and five floors above ground in the area of 73,877 m2, collapsed down to the basement floor very suddenly. It was a five-story reinforced concrete (RC) building. It had 4 floors in the underground and was built using a technique called “flat slab construction”. The collapse is the largest peacetime disaster in South Korean history in which 502 people died, 6 missing, and 937 sustained injuries. Construction of the Sampoong Department Store was completed in late 1989, and it opened to the public on July 7, 1990, attracting an estimated 40,000 people per day during the building’s 5 years in service.
After the collapse, intense investigation was conducted to find out the direct causes of the collapse. The methods used for investigation were (1) survey on the present collapse situation and ground condition, (2) strength test of the concrete and steel collected at the site, (3) design documents and construction/management reports, and (4) structural analysis. The investigation discovered that the Sampoong Department Store collapsed because of so many direct and indirect causes such as flaws in the design phase and mistakes in the construction and management process.
In April, 1995, cracks began to appear in the ceiling of the south wing’s fifth floor. During this period, the only response carried out by Lee and his management involved moving merchandise and stores from the top floor to the basement. The store management failed to shut the building down or issue formal evacuation orders, as the number of customers in the building was unusually high, and the store was not intending to lose potential revenue for that day. However, the executives themselves had left the premises as a precaution.
Seconds from Disasters – Sampoong Department Store Collapse
On the morning of June 29, the number of cracks in the area increased dramatically, prompting managers to close the top floor and shut the air conditioning off. Civil engineering experts were also invited to inspect the structure, with a cursory check revealing that the building was at risk of collapse. Five hours before the collapse, the first of several loud bangs were emitted from the top floors, as the vibrations in the air conditioning caused the cracks in the slabs to widen further. Amid customer reports of the vibrations, the air conditioning was turned off, but the cracks in the floors had already widened to 10cm.The store was packed with shoppers 52 minutes before the collapse, but the owner did not close the store or carry out repairs at the time. When the building started to produce cracking sounds at about 5:50 p.m., workers began to sound alarm bells and evacuate customers.The main columns, weakened to allow the insertion of the escalators, collapsed in turn, and the building’s south wing pancaked into the basement. Within 20 seconds, all of the building collasped.
It has been reported by the facility manager of the store that the roof had cracks appearing after Air Conditioning units (AC Units) were dragged across the roof floor 2 years before the collapse which also caused cracks to appear on the roof slabs surrounding the columns. These 15 tonnes AC units were moved to the other side of the building after nearby neighbours complained of the noise produced by these AC units. The impractical way of moving these super heavy AC units put too much stress onto the slabs that were pushed onto the column. It was not the columns that failed to carry the loads as the safety margin of the columns was still within the limit, however, it was due to the slab cracking that initiated the shear punching of the columns through the slabs. The slabs were damaged because of the way these AC units have been dragged across the roof floor. Another glitch is that the building was only designed for 4 floors but management decided to incorporate Restaurants which required the fifth floor to be added. The original construction company refused to give their consent prompting the store owner, out of utter foolishness for the benefit of the business, to hire his own ‘in house’ construction company to complete the work. An additional floor on top of the 4th-floor columns was inappropriate because the columns on the 4th floor had a diameter of approximately 60cm but with an additional fifth floor would need to have been 80cm. Another problem was that the reinforcement bars were not positioned correctly. The rebars were placed 10cm from the edge of the slab, 5cm off the required position. This causes the slab to lose 20% strength. These details, however, were not the cause of the collapse but reduced the overall strength of the RC frame. In Restaurants, because of traditional reasons, people sit on the floor to eat. Floor heating systems were therefore installed resulting in a thicker slab on the 5th floor; the heat and extra weight of the thickened slab has put even more stress on the RC columns on the 4th floor. The main cause of the collapse was unveiled when the facility manager of the store was interviewed. He mentioned customers complaining about strange noises that were being heard from the building which might have been due to the Air Conditioning Units that caused vibrations; this consequently prompted the facility manager to turn them off, but at that time it was too late as the crack around the columns widened up to 10cm. The vibrations of the AC units located on the roof was what kick-started the collapse. The vibrations that were radiating through the cracks of the floor were the final push that determined the fate of the building.
To conclude, all the mistakes within one building could have been prevented if only a single person made the right decision to evacuate the building. The structural engineer ‘hack su lee’ was informed about the incident of the cracking around the column on the fifth floor and immediately asked the owner of the Sampoong super store to evacuate the building because it was in danger of collapse and needed urgent repair. The owner of the building refuses and customers continue to enter the building until collapse. The collapse was blamed on ignorance and negligence by the owner of the store and their ‘in house’ chief architect with several others also charged. It is important to understand that any structural failures visible by the naked eye or any other evidence of abnormalities should be taken seriously. Any sign appearing to be threatening the structural integrity of a building can end up resulting in a deadly disaster. Any abnormalities within a building must be reported. It is Imperative to listen and cooperate with the Structural Engineer; in this case the Engineer warned that the building was in danger of collapse and that was the case.