Principles of Structural Design

Analysis of a structural collapse involves the study of the basic architectural principles, properties and operation of the different components of the structure, as well as knowledge of different possible causes of structural failure.
The Seongsu Bridge is 11th bridge constructed over the Han River in Seoul, South Korea. Construction of this cantilever bridge was set about on April 9, 1977 and completed on October 15, 1979, 2 years and 6 months later. It was a four-lane bridge with 19.4m width and 1,160.8m length [20].
It became infamous when it collapsed on October 21, 1994. The bridge collapsed early in the morning when one of its concrete slabs fell in to river due to a failure of the suspension structure. Around 07:40 hours on October 21, 1994, Seongsu Bridge connecting Seongsu-dong and Apgujeong-dong of Gangnam-gu, Seoul, collapsed. The slab (48 m) between the fifth and the sixth leg of the Bridge collapsed so 32 people died and 17 people were injured while they were on the way to office or school.
Seongsu Bridge is one part of arterial road that connects the Kanan district which is residential section in the southern in Seoul City and city center of Seoul City, and its has a lot of traffic volume. The steel truss digit division where the accident occurred was the 672m length, and it was one of the suspension digits of the center part. …
In addition, Seongsu Bridge complained that it had been trembling in motion, so the authorities in Seoul City also carried out the repair work of the emergency in the night in accident the previous day. It was said that the traffic jam arose, because especially, it was for commutation attending school hour in the accident-generation, and because the rain fell, the rolling stock was crowded [20].
Cause of collapse:
Various reasons can be associated with the collapse of bridge. Major of them are as listed below [19]:
Bad welding of the suspension which member of the I-type cross section, which was hanging the suspension digit of the center from the steel truss, seems to be a main cause.
There was visibility cutting corners between surface and splice plate of the fillet welding, so construction management and inspection method in the construction of Seongsu Bridge seemed to be remarkably slipshod.
Calcium chloride, which was scattered in order to prevent the road surface freezing, chloride ingress was uppued for the cracks by poor weld or stress corrosion, and so that the corrosion of steel product might be promoted.
There is a possibility to produce unexpected partial cracks in the steel surface because in the cross-sectional shape of suspension steel product, the cone angle ( the relaxation curved surface ) for easing stress concentration was insufficient.
Though there is no error at the content for the design, there was some possibility that the immature construction level was not sufficiently assumed.
There were no technical standards on in-service maintenance repair of Seongsu Bridge.
Because of the fiscal resource constraint (budget) of Seongsu Bridge while it was in service, the periodic check was