T.Y. Lin International
Project: Sanhao Bridge
Category: Design
Project Summary
This steel-concrete hybrid bridge’s story describes an innovative design that made it possible for a
prestressed concrete bridge girder to replace a steel girder. The new Sanhao Bridge crosses the
Hwun River in Shenyang, China. At a total length of 900m and a total width of 34m, this signature
bridge carries six lanes of city traffic and two 4.5-m wide pedestrian/bicycle paths. The main bridge
features two steel arch shaped towers that resemble a butterfly. The total length of the main spans is
270m. Built under a very limited budget, the bridge’s iconic and extravagant appearance was made
possible by the design innovations of T.Y. Lin International.
The original design was a spectacular cable-stayed bridge, one with both the tower and the girders designed in steel. In China, a steel girder costs twice as much as a concrete girder but weighs only a third of a typical concrete girder. Changing the girder to concrete would have reduced the cost of the girder, but due to its weight, a concrete girder would have required a significantly larger and more expensive tower. This was unacceptable, both aesthetically and economically.
To address this problem, an innovative design based on the partially cable-stayed girder bridge concept was developed (“Rethinking Bridge Design, A New Configuration,†Civil Engineering Magazine, July 2007). Here, the bridge was first designed as a girder bridge. Because the 2.6m girder depth was restricted by the required navigation clearance, the capacity of the prestressed concrete girder was not sufficient to resist the design loads of the 2x100m span bridge. Stay cables were then used to pick up the difference. For the Sanhao Bridge, the girder could carry approximately 60% of the loads. Therefore, the cables were only required to carry about 40% of the loads. This is quite different from a conventional cable-stayed bridge where the cables are typically designed to carry the entire loading—both dead and live loads of the girder. Cost reduction was achieved by replacing the steel girder with a concrete girder while the steel tower remains almost the same.
Use of a concrete girder boosted the local economy by utilizing local labor and materials. Eliminating most transportation from afar also was environmentally significant. In addition, the local climate is very humid and rainy and a concrete girder was much more preferable in this environment for long term durability and maintenance.
Taking advantage of the shallow water, the prestressed concrete girder was cast-in-situ on falsework. Once the girder was complete, the tower arches were assembled lying flat on top of the deck. A temporary tower was erected between the two arches and winches were used to raise the arch ribs to their final position before the final cables were installed. This operation took less than 12 hours.
This innovative, constructible design fulfills the City of Shenyang’s desire to create a city landmark while staying within the owner’s budget. A groundbreaking ceremony was held in Shenyang on November 28, 2006. The bridge opened to traffic October 10, 2008.
T.Y. Lin International has executed an original design, employing the principle of a partially cable-supported bridge that has an appearance unlike any other bridge in the world. The Sanhao Bridge in Shenyang, China revamps conventional thinking about how cable-supported bridges look and function. Instead of using cables as primary load carriers and girders as a secondary support, the roles of these two structural elements have been reversed: the girders carry 60 percent of the total load and the cables carry 40 percent. This structurally efficient configuration has made the project possible despite strict budgetary requirements.