Mott MacDonald in a consortium with Epsilon and Norconsult Civil Engineering undertook the feasibility study and preliminary and detailed design of the £128 million project for the Department of Rural Roads, Bangkok.
The feasibility study evaluated bridge options, together with bored and submerged tube tunnel options, along various alignments.
The study recommended constructing the bridge option for the north-south route between Rama III Road and Poochao Saming Phrai Road.
Navigation spans of the south and north cable stay bridges are 398m and 326m respectively with navigation clearances for shipping at 54m and 45 respectively. Pylons are reinforced concrete. Two planes of stay cables support the outer edges of the decks. Main span decks are of steel composite construction. Back span decks are of prestressed concrete with intermediate support and anchorage providing reaction to live loading forces imposed on the main deck.
The bridges are connected by high level viaduct complete with elevated junctions. Bridges and viaduct carry three lanes of traffic in either direction. Overall length of the project is more than 5km. Viaduct consists of continuous concrete box girders with spans varying between 64m for the high level viaducts and 36m for the lower viaducts.
The monumental scale of this project, within the low-lying landscape, required very careful consideration during the design stage. Our objective was to create a structure which had empathy with the rich Thai culture, not one merely seen as an international import. The design was created in collaboration with Yee Associates. The diamond form of the pylons was inspired by the pointed ceremonial hats of the Thai dancers and the temple roves.
The 14m high golden finials sit distinctively above the viewing platform on each pylon. The pylons are dimensioned for maximum visual effect and shaped to articulate light and shade in the concrete while giving a smooth, fair face finish.
The main span deck emphasises the modular construction by visually expressing the variable depth cross girders. The support stays are positioned inboard of the deck edge to maintain a continuous deck ribbon.
Special consideration was given to the visual interface between the suspended main spans and the back spans, which are conceived as extensions of the central interchange and approach viaducts.