The Sampoong Department Store collapse was a structural failure that occurred on June 29, 1995 in the Seocho-gu district of Seoul, South Korea. The collapse is the largest peacetime disaster in South Korean history – 501 people died and 937 were injured.
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 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 using 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 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%.