Sampoong Department Store Collapse: What Went Wrong

On the evening of 29 June 1995, the Sampoong Department Store in the Seocho district of Seoul collapsed in a matter of seconds while it was full of shoppers and staff. Five hundred and two people died and more than nine hundred were injured. The Sampoong Department Store collapse remains the deadliest peacetime disaster in South Korea’s history, and it is one of the most studied building failures in structural engineering.

This article explains the structure, the changes made to it, the warning signs in its final months and the mechanism that the investigators identified. It draws on the findings of the official investigation and the court proceedings that followed, and it is written with respect for those who died and for the families who still mark the anniversary.

The building and its structural system

The store was built on former landfill ground and completed at the end of 1989, opening in 1990. It was a reinforced concrete flat slab structure: the floors rested directly on columns, without beams, which gives clear, open floor plates well suited to retail. Flat slabs are efficient and widely used around the world, including in Singapore, but they have one critical vulnerability. Around each column the slab must transfer its entire share of the floor load into the column through a relatively small area of concrete. If that zone is overstressed, the column can punch through the slab, a failure known as punching shear.

Because there are no beams to catch a falling slab or to redistribute load, a punching failure at one column throws its load onto the neighbouring connections. If they too are near their capacity, the failure can spread across a floor and then down through the floors below. Our article on flat slab construction explains how designers guard against this with adequate slab depth, drop panels, column heads and shear reinforcement.

Changes during design and construction

The building was originally planned for a different use and was converted into a department store during construction. The investigation and later accounts describe a series of changes that each reduced the structure’s margin of safety:

Change of use. Retail floors carry heavier and more variable loads than the use originally planned, and the store layout required columns to be cut or modified, for example to accommodate escalators.
Smaller columns. Column sizes were reduced from what the original design called for, which also reduced the perimeter of slab available to resist punching shear at each column.
An additional floor. A fifth storey was added and used as a restaurant floor, with a heavy concrete base for traditional underfloor heating, adding substantial dead load to the top of the structure.
Reinforcement deficiencies. Investigators reported less reinforcement in columns than required and slab reinforcement placed in positions that reduced its effectiveness.

According to published accounts, the original contractor raised concerns about the alterations and was replaced. None of these changes was accompanied by a full re-engineering of the structure.

The rooftop plant and the final months

The rooftop carried large air-conditioning units. In 1993 these were moved across the roof to a new position, reportedly because of complaints about noise from neighbouring residents. Moving them dragged a heavy concentrated load over the roof slab, and their new position placed it over connections that were already weak. Cracks appeared and, over time, the vibration of the operating plant is understood to have worsened them.

By April 1995 cracks were appearing in the fifth-floor ceiling. On the day of the collapse they widened dramatically. Parts of the top floor were closed and the air conditioning was switched off, but the building was not evacuated. At about 5.52 in the evening, the slab-column connections at the top of the building gave way, and the failure ran down through the floors below. The south wing collapsed into the basement in around twenty seconds.

What the investigation found

The investigation ruled out a gas explosion and other external causes. It concluded that the collapse was a structural failure arising from a combination of design and construction deficiencies, unsafe modifications to the building and added loads, with the relocated rooftop plant acting as the trigger. The failure mechanism was punching shear at slab-column connections near the top of the building, followed by progressive collapse.

Later technical studies of the failure, using the investigation’s data, reached the same view: no single factor would necessarily have brought the building down, but together they removed almost every margin the structure had. The courts convicted the store’s chairman and its chief executive, along with officials found to have taken bribes in connection with the approvals.

Engineering lessons from the Sampoong Department Store collapse

The case is taught in engineering schools for several reasons.

Punching shear is unforgiving

Punching shear is a brittle failure. A beam that is overloaded in bending will usually crack and deflect visibly long before it fails. A slab-column connection can fail with far less warning and far less redistribution. The cracking that did appear at Sampoong was a sign that the connections were already close to their limit.

Every change needs re-analysis

A change of use, an added floor, a cut column, relocated plant: each of these is, in engineering terms, a new structure. In Singapore, changes of this kind are addition and alteration works that require a professional engineer’s design and approval, as explained in our guide to A&A works in Singapore.

Robustness matters

A structure that can find alternative load paths when one element fails gives its occupants time. Sampoong had no such reserve, and the failure became a progressive collapse.

Distress is a reason to evacuate

Widening cracks in slabs and around columns, especially in a flat slab building, are a serious warning. The appropriate response is immediate assessment by an engineer and, where there is doubt, evacuation.

Aftermath and memory

The Sampoong Department Store collapse, which followed the collapse of Seoul’s Seongsu Bridge less than a year earlier, prompted public anger, a review of building safety regulation in South Korea and scrutiny of corruption in the approval process. A memorial stands in Yangjae Citizen’s Forest in Seoul, and the site of the store has since been redeveloped.

For engineers in Singapore, the case has a particular resonance: it bears comparison with the Hotel New World collapse of 1986, where a building with too little margin also gave warning signs before it failed. Both are included in our overview of famous structural failures.

Frequently asked questions

What caused the Sampoong Department Store collapse?

The investigation found that the building failed through punching shear at slab-column connections near the top floor, followed by progressive collapse. The underlying causes were a combination of design and construction deficiencies, a change of use, reduced column sizes, an added floor and heavy rooftop plant that had been relocated over weak connections.

How many people died in the Sampoong collapse?

Five hundred and two people died and more than nine hundred were injured when the store collapsed on 29 June 1995. Some survivors were rescued from the debris many days after the collapse.

Were there warning signs before the collapse?

Yes. Cracks had appeared in the fifth-floor ceiling in the months before, and on the day of the collapse they widened rapidly. Parts of the top floor were closed, but the building was not evacuated before it failed in the early evening.

What is punching shear?

Punching shear is a failure in which a column pushes through the slab it supports, shearing a cone of concrete around the column. It is the critical check for flat slabs, which have no beams, and it is brittle, meaning it can occur with little warning once the connection’s capacity is exceeded.

Planning a change of use, an added floor or heavy plant on an existing building? Talk to our consultancy or get in touch before the work begins.