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Method of analysis and estimating performance of the interventions/
equipment/ services proposed for avoiding future failure.

 

In this section, an investigation of the cause of the
disaster will be carried out by analysing the structure and its surroundings.

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From the analysis, an estimation of the performance of interventions will be
given to avoid future failure.

 

Method of analysis

 

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.

 (source: https://ac.els-cdn.com/S0379073811005275/1-s2.0-S0379073811005275-main.pdf?_tid=ba2d4928-fcb6-11e7-85c0-00000aab0f02=1516324920_3eef3114ff6e1abb202920aa9da5c4ef)

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 damages.

Figure 2. Moving trace of cooling system.

(source: https://ac.els-cdn.com/S0379073811005275/1-s2.0-S0379073811005275-main.pdf?_tid=ba2d4928-fcb6-11e7-85c0-00000aab0f02&acdnat=1516324920_3eef3114ff6e1abb202920aa9da5c4ef)

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.

(source: https://ac.els-cdn.com/S0379073811005275/1-s2.0-S0379073811005275-main.pdf?_tid=ba2d4928-fcb6-11e7-85c0-00000aab0f02&acdnat=1516324920_3eef3114ff6e1abb202920aa9da5c4ef)

Another important point to add to the findings was the
omission of drop panel construction. Drop panels increase the shear strength of
the flat slab floor by handling with punching shear which is critical to flat
slab structure. The investigation proved that some pillars were reduced and
other did not have drop panels installed, reducing the overall strength of the
structure.

Figure 4.Punching shear. (source:https://www.researchgate.net/profile/Rwayda_Al_Hamd/publication/304024788/figure/fig1/AS:[email protected]/Figure-1-Schematic-diagram-of-a-flat-plate-structure-and-the-punching-shear-failure.ppm)

Failure preventions and performance estimations

As described, the construction and performance of the
building was clearly poor as the safety factor had been dramatically reduced.

The pillars experienced extreme shear failure on the 5th floor and
the roof leading to progressive destruction of the entire building.

Sampoong department store failure could have been prevented
if the original blue prints and structural calculations were followed during
the construction. The following ways for failure prevention are listed below as
case interventions:

Case 1 – 5th floor

This case is the clearest and easiest to evaluate among the
rest to prevent the failure of the department store. The 5th floor
was not included on the initial design as the building was specially designed
as a 4-floor department store. The restaurants and appliances have added
considerable weight increasing the dead load. If this had not been constructed,
the building would not have collapse on the 29th of June 1995.

Case 2 – Water cooling systems

The installation of water cooling systems on the roof added
had added more weight, specially when they were full of water. Due to
complaints, the systems were moved and dragged along the floor placing
concentrated stresses on the column, causing cracks up to 25mm wide according
to investigations. These heavy cooling blocks could had been lifted by using a
crane to prevent structural damages on the building. The vibrations caused by
the cooling blocks when operating also contributed to widen the cracks produced
on the floor This was also prevented by adding more columns to distribute the
load of the cooling system.

Case 3 –  Irregular
construction

According to the structural drawings, the pillars on the 4th
floor and 5th floor were designed to be 80 cm diameter. However,
some of the columns were 80 cm diameter such as pillar of C1A and
some other were reduced to 60 cm diameter with 22 mm of reinforced bar as seen above
in Figure 3. By regulating the size of the columns and reinforcement bars
throughout the entire floor would have contribute to reducing the possibility
of the collapse.

 

Figure 5.Comparison
of columns between structural calculations and design.

(source: https://ac.els-cdn.com/S0379073811005275/1-s2.0-S0379073811005275-main.pdf?_tid=ba2d4928-fcb6-11e7-85c0-00000aab0f02&acdnat=1516324920_3eef3114ff6e1abb202920aa9da5c4ef)

Case 4 – Drop panel construction omission

As mentioned, sizes of several pillars were reduced and drop
panel construction were omitted on the columns. The force from the slab is
transfer to the drop panel and consequently, transfers it to the column. Drop
panel construction helps to distribute the load applied to the slab by reducing
the stress concentrated on the column area. If drop panel had been kept,
possibility of punching shear would had been reduced positively.

Analysis of the stress of the structure was carried out by
using FEA software such as Siemens NX. The following images, graphically shows the
stress concentration and distribution when the load is applied on a column:

Without drop panel construction

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