Methodof analysisThe analysis was first started with thepossibility of earthquakes although South Korea was in a stable landmass. Theseismic charts indicated no earthquakes activity on the day of this incident.
There was a possibility of act ofterror from communist North Korea as 50 years after the Korean War, the twocountries are still in strong military tension. This possibility was discard asthere was no trace of act of terror after inspecting the rubble.The investigation of the collapse ofthe department store was continued with inspection of the ground as after thecollapse, a part of the building stayed standing while other part ended up inrubbles. The ground was originally a landfillbefore the construction of the store, therefore further inspection of thefoundation was imperative to verify that the land. After studying the land bydrilling deep into the buildings foundation, concluding that the groundstructure beneath the construction was solid enough for the department store asthis was firmly attached to a layer of bed rocks. The building was based in flat slabconstruction which is popular and cheap choice for buildings. This type ofconstruction is strong than any other but required to be planned andconstructed precisely.
As the building was made on a solid land, it wassuspected that construction of the department store could had caused thecollapse. Sample of concrete was examined thoroughly in a laboratory to testthe strength by using a compressor. To achieve strong and solid concrete, thecomponents must be precisely mixed. The examination concluded that the concretewas solid enough for the building.The investigation continued byexamining the original blue prints of the building and hints of the collapsewere hidden on them.
During the construction of the store, the originalconstruction company hired for building were not allowed to finish thestructure as the executives demanded several design modifications of the buildings.According to the engineers, the modifications could put the people and theentire construction at risk. The original construction company wasreplaced by another one as the boss wanted to continue with the modifications.The danger was ignored, and the construction continued to meet the executive’splans.Originally, the building was onlydesigned for 4 floors. However, as mentioned, management wanted to incorporatea fifth floor. The modifications were based on the fifth floor which wasoriginally designed for roller skating rink. However, this was replaced by afloor of restaurant.
This multiplied the weight of the floor by 3 times due torestaurants and its appliances. Moreover, Korean restaurants normally usedwater pipes for heating systems travelling through the floor. Therefore, thefloor thickness had to be increased by 30 cm, adding more weight than thestructural calculation.
Figure 12 – Design and real loadof 5th floor (T. Won Park, 2012).Furthermore, investigators found thathuge water cooling systems that weigh around 30 tonnes were moved along thefloor due to neighbours’ complaints. This action put the slabs into hugestresses leading into irreversible damages.
The structural drawings indicated that 16 columns on 4th and5th floor were designed to be 80 cm diameter. However, this werereplaced by 8 pillars of 60cm of diameter with 22 mm diameter of reinforcedbar. 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 14 -Reduction of cross sectional area of columns. (T.
Won Park, 2012)Another important point to add to thefindings was the omission of drop panel construction. Drop panels increase theshear strength of the flat slab floor by handling with punching shear which iscritical to flat slab structure. The investigation proved that some pillarswere reduced and other did not have drop panels installed, reducing the overallstrength of the structure.Figure 15- Punching Shear Failurepreventions and performance estimations.As described, the construction andperformance of the building was clearly poor as the safety factor had beendramatically reduced. The pillars experienced extreme shear failure on the 5thfloor and the roof leading to progressive destruction of the entire building.Sampoong department store failure couldhave been prevented if the original blue prints and structural calculationswere followed during the construction. The following ways for failureprevention are listed below as case interventions:Case 1 – 5th floorThis case is the clearest and easiestto evaluate among the rest to prevent the failure of the department store.
The5th floor was not included on the initial design as the building wasspecially designed as a 4-floor department store. The restaurants andappliances have added considerable weight increasing the dead load. If this hadnot been constructed, the building would not have collapse on the 29thof June 1995.
Case 2 – Water cooling systemsThe installation of water coolingsystems on the roof added had added more weight, specially when they were fullof water. Due to complaints, the systems were moved and dragged along the floorplacing concentrated stresses on the column, causing cracks up to 25mm wideaccording to investigations. These heavy cooling blocks could had been liftedby using a crane to prevent structural damages on the building. The vibrationscaused by the cooling blocks when operating also contributed to widen thecracks produced on the floor This was also prevented by adding more columns todistribute the load of the cooling system.Case 3 – Irregular constructionAccording to the structural drawings,the pillars on the 4th floor and 5th floor were designedto be 80 cm diameter. However, some of the columns were 80 cm diameter such aspillar of C1A and some other were reduced to 60 cm diameter with 22mm of reinforced bar as seen above in Figure 3. By regulating the size of thecolumns and reinforcement bars throughout the entire floor would havecontribute to reducing the possibility of the collapse.
Figure 16 -Comparison of columns between structural calculations and design. (T. Won Park,2012) Case 4 – Drop panel constructionomissionAs mentioned, sizes of several pillarswere reduced and drop panel construction were omitted on the columns. The forcefrom the slab is transfer to the drop panel and consequently, transfers it tothe column.
Drop panel construction helps to distribute the load applied to theslab by reducing the stress concentrated on the column area. If drop panel hadbeen kept, possibility of punching shear would had been reduced positively.Analysis of the stress of the structurewas carried out by using FEA software such as Siemens NX. The following images,graphically shows the stress concentration and distribution when the load isapplied on a column:Without drop panel constructionWith drop panel construction