In this section, an investigation of the cause of the
disaster will be carried out by analysing the structure and its surroundings.
From the analysis, an estimation of the performance of interventions will be
given to avoid future failure.
Process of analysis of the incident
The analysis was first started with the possibility of
earthquakes although South Korea was in a stable landmass. The seismic charts
indicated no earthquakes activity on the day of this incident.
There was a possibility of act of terror from communist
North Korea as 50 years after the Korean War, the two countries are still in
strong military tension. This possibility was discard as there was no trace of
act of terror after inspecting the rubble.
The investigation of the collapse of the department store
was continued with inspection of the ground as after the collapse, a part of
the building stayed standing while other part ended up in rubbles.
The ground was originally a landfill before the construction
of the store, therefore further inspection of the foundation was imperative to
verify that the land. After studying the land by drilling deep into the
buildings foundation, concluding that the ground structure beneath the
construction was solid enough for the department store as this was firmly
attached to a layer of bed rocks.
The building was based in flat slab construction which is popular
and cheap choice for buildings. This type of construction is strong than any
other but required to be planned and constructed precisely. As the building was
made on a solid land, it was suspected that construction of the department
store could had caused the collapse. Sample of concrete was examined thoroughly
in a laboratory to test the strength by using a compressor. To achieve strong
and solid concrete, the components must be precisely mixed. The examination
concluded that the concrete was solid enough for the building.
The investigation continued by examining the original blue
prints of the building and hints of the collapse were hidden on them. During
the construction of the store, the original construction company hired for building
were not allowed to finish the structure as the executives demanded several design
modifications of the buildings. According to the engineers, the modifications
could put the people and the entire construction at risk.
The original construction company was replaced by another
one as the boss wanted to continue with the modifications. The danger was ignored,
and the construction continued to meet the executive’s plans.
Originally, the building was only designed for 4 floors. However,
as mentioned, management wanted to incorporate a fifth floor. The modifications
were based on the fifth floor which was originally designed for roller skating
rink. However, this was replaced by a floor of restaurant. This multiplied the
weight of the floor by 3 times due to restaurants and its appliances. Moreover,
Korean restaurants normally used water pipes for heating systems travelling through
the floor. Therefore, the floor thickness had to be increased by 30 cm, adding
more weight than the structural calculation.
Figure 1. Design and real load of 5th floor.
Furthermore, investigators found that huge water cooling
systems that weigh around 30 tonnes were moved along the floor due to neighbours’
complaints. This action put the slabs into huge stresses leading into irreversible
Figure 2. Moving trace of cooling system.
The structural drawings indicated that 16 columns on 4th
and 5th floor were designed to be 80 cm diameter. However, this were
replaced by 8 pillars of 60cm of diameter with 22 mm diameter of reinforced
bar. This changes the structure of the floor by including two types of pillars,
reducing 56.3% of the cross-sectional area and 50% reduction of reinforced bar.
Figure 3. Reduction of cross sectional area of columns.
Another important point to add to the findings was the omission
of drop panel construction.