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 thedisaster will be carried out by analysing the structure and its surroundings.From the analysis, an estimation of the performance of interventions will begiven to avoid future failure. Method of analysis The analysis was first started with the possibility ofearthquakes although South Korea was in a stable landmass. The seismic chartsindicated no earthquakes activity on the day of this incident.There was a possibility of act of terror from communistNorth Korea as 50 years after the Korean War, the two countries are still instrong military tension.
This possibility was discard as there was no trace ofact of terror after inspecting the rubble.The investigation of the collapse of the department storewas continued with inspection of the ground as after the collapse, a part ofthe building stayed standing while other part ended up in rubbles. The ground was originally a landfill before the constructionof the store, therefore further inspection of the foundation was imperative toverify that the land. After studying the land by drilling deep into thebuildings foundation, concluding that the ground structure beneath theconstruction was solid enough for the department store as this was firmlyattached to a layer of bed rocks. The building was based in flat slab construction which ispopular and cheap choice for buildings. This type of construction is strongthan any other but required to be planned and constructed precisely. As thebuilding was made on a solid land, it was suspected that construction of thedepartment store could had caused the collapse. Sample of concrete was examinedthoroughly in a laboratory to test the strength by using a compressor.
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Toachieve strong and solid concrete, the components must be precisely mixed. Theexamination concluded that the concrete was solid enough for the building.The investigation continued by examining the original blueprints of the building and hints of the collapse were hidden on them. Duringthe construction of the store, the original construction company hired forbuilding were not allowed to finish the structure as the executives demandedseveral design modifications of the buildings. According to the engineers, themodifications could put the people and the entire construction at risk.
The original construction company was replaced by anotherone 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. Themodifications were based on the fifth floor which was originally designed forroller skating rink. However, this was replaced by a floor of restaurant. Thismultiplied the weight of the floor by 3 times due to restaurants and itsappliances.
Moreover, Korean restaurants normally used water pipes for heatingsystems travelling through the floor. Therefore, the floor thickness had to beincreased 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 coolingsystems that weigh around 30 tonnes were moved along the floor due toneighbours’ complaints. This action put the slabs into huge stresses leadinginto 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 4thand 5th 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 3. Reduction of cross sectional area ofcolumns. (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 theomission of drop panel construction. Drop panels increase the shear strength ofthe flat slab floor by handling with punching shear which is critical to flatslab structure. The investigation proved that some pillars were reduced andother did not have drop panels installed, reducing the overall strength of thestructure.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 estimationsAs described, the construction and performance of thebuilding was clearly poor as the safety factor had been dramatically reduced.The pillars experienced extreme shear failure on the 5th floor andthe roof leading to progressive destruction of the entire building.
Sampoong department store failure could have been preventedif the original blue prints and structural calculations were followed duringthe construction. The following ways for failure prevention are listed below ascase interventions:Case 1 – 5th floorThis case is the clearest and easiest to evaluate among therest to prevent the failure of the department store. The 5th floorwas not included on the initial design as the building was specially designedas a 4-floor department store.
The restaurants and appliances have addedconsiderable 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 systemsThe installation of water cooling systems on the roof addedhad added more weight, specially when they were full of water.
Due tocomplaints, the systems were moved and dragged along the floor placingconcentrated stresses on the column, causing cracks up to 25mm wide accordingto investigations. These heavy cooling blocks could had been lifted by using acrane to prevent structural damages on the building. The vibrations caused bythe cooling blocks when operating also contributed to widen the cracks producedon the floor This was also prevented by adding more columns to distribute theload of the cooling system.Case 3 – IrregularconstructionAccording to the structural drawings, the pillars on the 4thfloor and 5th floor were designed to be 80 cm diameter. However,some of the columns were 80 cm diameter such as pillar of C1A andsome other were reduced to 60 cm diameter with 22 mm of reinforced bar as seen abovein Figure 3. By regulating the size of the columns and reinforcement barsthroughout the entire floor would have contribute to reducing the possibilityof the collapse.
Figure 5.Comparisonof 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 omissionAs mentioned, sizes of several pillars were reduced and droppanel construction were omitted on the columns. The force from the slab istransfer to the drop panel and consequently, transfers it to the column.
Droppanel construction helps to distribute the load applied to the slab by reducingthe 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 byusing FEA software such as Siemens NX.
The following images, graphically shows thestress concentration and distribution when the load is applied on a column:Without drop panel construction