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Sunday, 27 July 2014

Turning Back our Pendulum: Sampoong Departmental Store Collapse in Eulhae Year (1995)

Long time ago - before the Sewol-ho Sinking Incident in 2014, the present-day Daelim Acrovista Apartments has recorded the bleakest moment of Sampoong Departmental Store Collapse in 1995. The site of the ill-fated shopping complex is located at 188 Seocho Central Avenue/SeochoJungangno, Seocho-dong 1685-3 beonji, Seoul Seocho-gu. Eulhae (을해/乙亥 - Yin Wooden Boar) derives from the Sexagenary Cycle's 12th year of Sino-Korean Calendar

I choose this crucial subject because I am currently studying in Diploma of Civil Engineering at Port Dickson Polytechnic and suitable for me as a future civil engineer. The collapse is not only caused by structural overload and punching shear but this includes manslaughter of the innocent people inside the building. Bear in mind that contractor is fully responsible on this worst-case scenario.

The Sampoong Department Store Collapse (Hangul/Hanja/Romanization: (삼풍백화점 붕괴사고/三豊百貨店崩壞事故/Sampoong-baekhwajeom Bunggoe Sago) was a structural failure that occurred on June 29, 1995, in the Seoul Seocho-gu, South Korea. The collapse is the largest peacetime disaster in South Korean history as 502 people died and 937 were injured. It was the deadliest building collapse since the Circus Maximus collapse in c. 140 AD and until the September 11 attacks in New York City, and the deadliest non-terror-related building collapse until the 2013 Savar building collapse near Dhaka.

Sampoong Departmental Store, before the collapse of the complex
The Sampoong Group, a South Korean trade company began construction of the Sampoong Department Store in 1987 over a tract of land previously used as a landfill. Originally designed as a residential apartment with four floors, it was changed to a large department store during its construction by Lee Joon, the future chairman of the building. This involved cutting away a number of support columns in order to install escalators. When the original contractors refused to carry out these changes, Lee ignored their warnings and fired them, instead using his own building company to complete construction.

The building was completed in late 1989, and the Sampoong Department Store opened to the public on July 7, 1990, attracting an estimated 40,000 people per day during the building's five years of existence. The store consisted of north and south wings, connected by an atrium.

A fifth floor originally planned to house a skating rink was added later in the building's life to comply with zoning regulations that prevented the whole building from being used as a department store. However, Lee changed the original plan for the fifth floor to include eight restaurants instead. When a construction company tasked to complete the extension advised that the structure would not support another floor, they were fired, and another company was hired to complete the project. The restaurant floor also had a heated concrete base with hot water pipes going through it, as patrons sit on the floor of traditional Korean restaurants, which added a large extra load due to the increase in thickness of the concrete slab.

In addition, the building's air conditioning unit was installed on the roof, creating a load of four times the design limit. Two years before the collapse, the air conditioning units were moved across the delicate roof, which is where the cracking started. The units were moved over the column 5E from which the most visible cracks in the floor of the fifth level were seen before the collapse.

The collapsed Sampoong Departmental Store
In April 1995, cracks began to appear in the ceiling of the south wing's fifth floor. During this period, the only response by Lee and his management staff involved moving merchandise and stores from the top floor to the basement.

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. 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 they did not want to lose the day's revenue. However, the executives themselves left the premises as a precaution.

Civil engineering experts were invited to inspect the structure, with a cursory check revealing that the building was at risk of collapse; the National Geographic documentary series Seconds From Disaster indicates that the facility's manager was examining the slab in one of the restaurants on the fifth floor, eight hours before the collapse, when, unknowingly, vibration from air conditioning was radiating through the cracks in the concrete columns and the floor opened up.

Five hours before the collapse, the first of several loud bangs was heard emanating from the top floors, as the vibration of the air conditioning caused the cracks in the slabs to widen further. Amid customer reports of vibration, the air conditioning was turned off, but the cracks in the floors had already grown to 10 cm wide.

At about 5:00 p.m. Korea Standard Time (UTC+9:00), the fifth floor ceiling began to sink, resulting in store workers blocking customer access to the fifth floor. According to Seconds From Disaster, the store was packed with shoppers 57 minutes before the collapse, but the owner did not close the store or carry out repairs at that time. When the building started to produce cracking sounds at about 5:52:30 p.m., workers began to sound alarms and evacuate the building, but by then it was too late.

Around 5:52:30 p.m., the roof gave way, and the air conditioning units crashed through into the already-overloaded fifth floor. 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's columns in the south wing gave way, trapping more than 1,500 people and killing 502. The disaster resulted in about ₩270 billion (approximately US$216 million) worth of property damage.

Rescue crews were on the scene within minutes of the disaster, with cranes and other heavy equipment being brought in the next day. However, authorities announced that they would call off the rescue, due to the danger that the unstable remains of the store could come down, and many of the rescuers would be at risk. Massive protests, especially from friends and relatives of those still missing, compelled officials to continue looking for survivors, with the remains of the store being steadied by guide cables. After nearly a week, the focus was on removing the debris, though construction crews were careful to check for victims.

Two days after the collapse, some officials said that anybody who was still in the building must have already died; therefore, further efforts would be made only towards "recovery", not "rescue". This conflicts with the fact that other people can survive much longer. Despite the sweltering heat, those who were not rescued in the first few days were able to avoid dehydration by drinking rainwater. The last to be rescued, 19-year-old Park Seung-hyun (박승현/朴昇賢), was pulled from the wreckage 17 days after the collapse with a few scratches. She said that she heard the sounds of other survivors drowning in the fire department's deflation water.

The investigation committee and effort was headed by Professor Lan Chung of Dankook University's engineering school. It was heavily detailed in an episode of Seconds from Disaster. Shortly after the collapse, leaking gas was suspected as the probable cause because two gas explosions had occurred elsewhere in the city that year. However, fires amid the rubble were from burning automotive gasoline coming from crushed cars parked in the underground garage, whereas a gas explosion would have been a massive inferno. In addition, it was widely feared that there had been a terrorist attack, with North Korea as the prime suspect. However, the fact the building collapsed downward instead of horizontally ruled out this possibility according to U.S. and South Korean experts.

Initially, it was believed the building's poorly-laid foundation, and the fact it was built on unstable ground, led to the failure. Investigation of the rubble revealed that a substandard concrete mix of cement and sea water and poorly reinforced concrete was used for the ceilings and walls.

Further investigation revealed the building was built with incorrect application of a technique called "flat slab construction". Reinforced concrete buildings are often built using columns and beams, with the floor slab supported over the full length of the beams. "Flat slab construction" does not use beams, but supports the floor slab directly on the columns. The area of floor around the columns must be reinforced in order to carry the load; even then, if the columns are too narrow, they can punch through the slab. However, plans of the Sampoong Department Store building showed the concrete columns were only 60 cm in diameter, below the required 80 cm. Worse still, the number of steel reinforcing bars embedded into the concrete was 8, not the required 16, giving the building only half its needed strength. Steel reinforcements intended to strengthen the concrete floor were placed 10 cm from the top instead of 5 cm, decreasing the structure's strength by about another 20%.

Ironically, one of the changes that contributed to the collapse was the installation of a safety feature. Fire shields were installed around all escalators to prevent the spread of fire from floor to floor, but in order to install them, the builders cut into the support columns, reducing their diameter further. The reduced diameter concentrated the burden on a smaller area of supported slab, leading to an eventual puncturing of the slab.

These factors, along with the addition of a fifth floor including restaurants and heavy restaurant equipment, collectively contributed to the building's eventual failure. Although the original building design would have been more than twice as strong as needed to remain erect, the flawed structure managed to stand for five years.

Investigators finally pinpointed the direct cause of the collapse, known as the "trigger" or tipping point, in the building's history. It was revealed that the building's three rooftop air-conditioning units had been moved in 1993 due to noise complaints from neighbours on the east side of the building. The building's managers admitted noticing cracks on the roof during the move, but instead of lifting them with a crane, the units were put on rollers and dragged across the roof, further destabilizing the surface due to each unit's immense weight. Cracks formed in the roof slabs and the main support columns were forced downward; column 5E took a direct hit, forming cracks in the position connected to the fifth-floor restaurants. According to survivor accounts, each time the air conditioners were switched on the vibrations radiated through the cracks, reaching the supporting columns and widening the cracks, over the course of two years. On the day of the tragedy, although the units were shut off, it was too late; the structure had suffered irreversible damage, and the fifth floor slab around column 5E finally gave way.

Lee Joon was charged with criminal negligence and received a prison sentence of ten and a half years. However, Joon's sentence was reduced to seven years on appeal in April 1996. Joon died of health complications on October 4, 2003, a few days after being discharged, relating to heart failure, high blood pressure and diabetes.

His son, Lee Han-sang, the store's president, who is now working for religious causes in Mongolia, faced seven years for accidental homicide and corruption. City officials Lee Chung-woo and Hwang Chol-min, in charge of overseeing the construction of the building, were also found to have been bribed into concealing the illegal changes and poor construction. As a result, the participating officials, including a former chief administrator of the Seocho-gu district, were also jailed. Other parties sentenced included a number of Sampoong Department Store executives and the company responsible for completing the building. The settlement involved 3,293 cases, totaling ₩375.8 billion (about $350 million USD). The former Chaebol Lee family was stripped of all of their possessions and assets to cover the costs and as result Sampoong Group was disbanded.

The initial reaction was enormous public outrage that led to months of demonstration on the streets. The disaster later led to skepticism and fears regarding safety standards on other engineering projects undertaken as South Korea experienced an economic boom during the 1980s and 1990s, and resulted in a review of South Korean safety regulations; the incident also revealed the level of corruption among city officials, who were willing to accept payoffs with little regard for public safety.