AN EXTRADOSED PRESTRESSED CONCRETEBRIDGE: KEONG AN BRIDGE (KOREA)
Abstract
In 2001, SYSTRA worked with Hyundai Engineering &Construction Co. (HDEC) and Dong-Il Engineering company, inorder to answer a turnkey design and construction competitionfor the Songnam-Janghowon highway project in Korea. The mainbridge on this highway is the Keong An bridge. SYSTRA designedan extradosed prestressed concrete bridge to cross the river. Thisbridge has three spans: 70 – 130 – 70 m. The deck is 30 m wide.It carries three lanes in both directions. A central plane waschosen for the extradosed cables, for aesthetic reasons. Due tothe moderate span (130 m), it is not necessary to have variabledepth for the deck. The deck is then easier to build. The deck islongitudinally prestressed by:– cantilever internal tendons placed in the top slab (12T15),– continuity internal tendons placed in the bottom slab in thecentral span (12T15),– continuity external tendons placed in the main and side spans(19T15), which are anchored next to the extradosed cablesconcrete anchorage blocks.External prestressing cables are deviated by diaphragms. Thereare seven extradosed cables on bothsides of the pylon, spaced5m at deck level in a semi-fan configuration, and deviated in thepylons through steel saddles. Saddles have been used instead ofdouble anchorages in the pylons, because it is more economical,and it allows designing a more slender pylon. The extradosedcables are adjustable (their tension can be adjusted duringservice life) and replaceable. Unbalanced extradosed cablesforces on both sides of the pylon are transmitted to the pylonthrough steel rings welded to the internal steel pipes.Main piers are made of a central circular shaft, 5 m diameter atthe base, two transverse inclined shafts and a pier cap. The piercap is prestressed with 8 x 19T15 tendons. The bridgeconstruction was finished in 2013.
