Bridge analysis, design + assessment

Case Study

Deck segment analysis for Yi Sun-sin Bridge

  • 4th longest suspension bridge in the world

  • Linear static analysis of twin box steel deck segments

  • Diaphragm design strengthened and optimised

Yooshin Engineering Corporation used LUSAS Bridge analysis software to carry out a detailed analysis of a 6 metre long twin-box steel girder deck segment for use on the Yi Sun-sin Bridge in Yeosu City, Cheonnam, South Korea on behalf of its client the Cheonnam Provincial Government. The bridge links Gwangyang to Yeosu city. The bridge is named in honour of a famous Korean sea hero, Admiral Yi Sun-sin, an enormous statue of whom will overlook the bridge. He was born in 1545 and which, by deliberate design, is also the length of the main span of the bridge in metres


The bridge is a three-span suspension bridge of 357.5 + 1545 + 357.5 metre spans which, at a total of 2260 metres in length, and when completed will be the fourth longest in the world. Concrete towers are H-shaped and at a height of 270 metres are the highest in the world. The height from sea level to the underside of the deck is in the order of 85 metres to allow for the largest container ships in the world to pass safely beneath the bridge. Preliminary design commenced in 2006 with detailed design work taking place throughout 2007. Understanding how the twin box girder deck section would behave under all loading conditions was difficult to ascertain so LUSAS Bridge analysis software was chosen to carry out a detailed analysis.

Modelling and Analysis

Using LUSAS, all webs, flanges, ribs and other small members in the 6 metre long deck segment were modelled. Vertical supports were placed at the hanger positions, and moment supports were placed along edges where deck sections would join to ensure the localised model would correctly match the global behaviour of the bridge. 

Vertical and moment supports on segment model

Four-lane Korean DB24 truck loading was applied as well as lane and distributed loadings, and a linear static analysis was carried out. In all, 6 load combinations consisting of 24 different vehicle loadings and dead loads were analysed and investigated using the range of results processing facilities available. 

Deck segment cross-section showing typical loading on segment

Slice sections through the diaphragm were taken in areas of interest and both principal stress and von-Mises stress were compared with the allowable stress for the SM490 steel members of the diaphragm and transverse box. From the detailed LUSAS analysis it was seen that the main structural behaviour was in the transverse direction, and, as result, it was seen that the initial diaphragm design needed to be strengthened. Typical results plots follow:

Typical deck segment stress results plot

Slice section stress results plot

Typical deck segment stress results plot

Slice section stress results plot

Construction of the bridge started at the end of 2007 and completion is scheduled for early 2012. Total project cost is in the region of 434 billion Won.


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