DYNA Grip^® System for South Korea’s first Curved Stay Cable Bridge

South Korea’s first stay cable bridge to feature a curved layout is currently being built near the city of Gwangyang, in the southern part of the country. Sae Poong Bridge is part of Gwangyang’s new bypass National Road No. 2 and will considerably improve the region’s traffic flow.

The 875m long stay cable bridge, which was designed by the Daelim Consortium, has a total of three vertical pylons that are centrally placed in the cross-section of the superstructure. The pylons have heights of 86.7, 101 and 88m, with the middle pylon being the tallest at a height of 101m. The individual spans measure 85 + 220 + 220 + 85m. The bridge deck is 23.9m wide and is designed to accommodate two lanes in each direction. The bridge deck is being built on falsework from the approach structures to the side spans. In the main span area, the bridge deck is being built using the cantilever construction method.

In July 2008, DSI was awarded the contract to supply all of the stay cables needed for this major project. The main stay cables that were used are 64 Type DG-P55 and 26 Type DG-P61 DYNA Grip^® Stay Cables.

Due to the curved layout, the construction geometry of Sae Poong Bridge is very complex. The stay anchorages at the bridge deck follow the curve; thus, the cable forces include a horizontal component at the pylon anchorage introducing lateral bending moments. In order to compensate for these bending moments, the pylons are laterally stayed using transverse stay cables. All in all, DSI supplied 12 Type DG-P12, 8 Type DG-P37 and 4 Type DG-P61 DYNA Grip^® Stay Cables for this purpose. In addition, DSI supplied 6 Type DG-P19 DYNA Grip^® Stay Cables that will act as tiedown cables to prevent lifting of the bridge deck at the abutments. Within the scope of the construction of Sae Poong Bridge, DSI developed two innovative solutions that we would now like to present to you.

Clevis Anchorage

Due to the fact that the transverse stay cables are positioned at a very steep angle to the pylon, they had to be anchored to the outsides of the pylons using special Clevis Anchorages that were newly developed by DSI (cf. DSI-Info 17 article on p. 114). These transverse stay cables are completely preassembled on site, including the strands. As the strands will no longer be accessible after installing the clevis anchorage, their wedges were hydraulically power seated in order to prevent slipping during lifting and subsequent stressing. Afterwards, the clevis anchorage, which features an inside thread, was threaded onto the anchor block instead of the usual ring nut. As these components weigh up to 1,000kg, a turning device had to be designed and supplied by DSI. For final assembly, the transverse cable was lifted by a crane and anchored to the gusset plate at the upper part of the exterior of the pylon using a pin. The first fatigue test for the new clevis anchorage was carried out successfully in accordance with fib Bulleting 30 for Type DG-P61 DYNA Grip^® Stay Cables at the Technical University of Munich in 2009.

Slim Sheathing

Another special feature of this project is the slim HDPE sheathing used by DSI. This feature had been requested in the project specifications in order to reduce the lateral wind load on the cables, which in turn allows for the use of a slimmer pylon and results in savings that carry all the way down to and include the foundation. DSI used these small diameter slim ducts for the first time on the Sae Poong Bridge. Thus, the outer diameter of the ducts for Type DG-P61 cables was reduced from 225mm to 200mm and from 200 to 180mm for Type DG-P55 cables. DSI developed a new installation method and new equipment in order to accommodate the demanding conditions caused by the smaller diameter and subsequent high degree of filling of the sheathing.

Construction work on this special major project began in August 2009 and is scheduled for completion in July 2012.