...The Sampoong Group began construction of the Sampoong Department Store in 1987 over a tract of land previously used as a landfill. The building's plans originally called for a residential apartment building with four floors, to be built by Woosung Construction.[3] However, during construction, the blueprints were changed by the future chairman of Sampoong Group's construction division, Lee Joon, to instead create a large department store. This involved cutting away a number of support columns to install escalators, and the addition of a fifth floor.[3][4][5]
After Woosung refused to carry out the changes, Lee ignored their warnings and fired them, using his own company to complete the construction.[3][5] 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.[5]
The completed building was a flat-slab structure without crossbeams or a steel skeleton, which effectively meant that there was no way to transfer the load across the floors. To maximise the floor space, Lee Joon ordered the floor columns to be reduced to be 60 cm (24 in) thick, instead of the minimum of 80 cm (31 in) in the original blueprint that was required for the building to stand safely, and the columns were spaced 11 metres (36 ft) apart to maximize retail space, a decision that meant that there was more load on each column than there would have been if the columns were closer together.
A fifth floor was originally planned to house a roller skating rink, added later to comply with zoning regulations that prevented the entire building from being used as a department store.[3][5] However, Lee Joon changed the plan for the fifth floor to include eight restaurants instead.[3] The construction company tasked with completing the extension advised that the structure would not support another floor, but was promptly fired, with another company being hired to complete the project. The restaurant floor had a heated concrete base referred to as ondol, which has hot water pipes going through it; the presence of the 1.2-metre-thick (4 ft) ondol greatly increased the weight and thickness of the slab.[3]
In addition, the store's three 15-tonne air conditioning units were also installed on the roof, creating a 45-tonne (50-ton) load that was four times the design limit. In 1993, the air conditioning units were dragged across the delicate roof, resulting in cracking.[5] The units were moved over column 5E, where the most visible cracks in the floor of the fifth level were seen before the collapse. The cracks in the columns worsened because the columns supporting the fifth floor were not aligned with the ones supporting lower floors, causing the load of the fifth floor to be transferred through the slab.[3]