Segmental bridge explained
As its name implies, a segmental bridge is a bridge built in short sections (called segments), i.e., one piece at a time, as opposed to traditional methods that build a bridge in very large sections. The bridge is made of concrete that is either cast-in-place (constructed fully in its final location) or precast concrete (built at another location and then transported to their final location for placement in the full structure).
These bridges are very economical for long spans (over 100 meters), especially when access to the construction site is restricted. They are also chosen for their aesthetic appeal.
The first segmental concrete bridge, built in 1950, was cast-in-place across the Lahn River in Balduinstein, Germany.
The first precast segmental concrete bridge, built in 1962, crossed the Seine River in France.
The first U.S. precast segmental concrete bridge, built in 1973, was built in Corpus Christi, Texas.
The first U.S. cast-in-place segmental bridge, built in 1974, was built near San Diego, California.
The first U.S. precast segmental concrete arch bridge is the Natchez Trace Parkway Bridge, completed in 1993.
The sequence of construction is similar to traditional concrete bridge building, i.e., build the support towers (columns), build the temporary falsework, build the deck, perform finish work. The principle differences are as follows:
- The support towers may be built segmentally. Often this is accomplished using "slip-form" construction, where the falsework moves (slips) upward following sequential concrete "pours." The falsework uses the newly constructed concrete as the basis for moving upward.
- After the towers are built, a superstructure is built a top the towers. This superstructure serves as the "launching" point for building the deck. (The deck is often built in both directions away from the tower, simultaneously.)
- The deck is now constructed sequentially, beginning at the tower, one section at a time.
- In cast-in-place bridges, the falsework is connected to the previously installed concrete and allowed to cantilever freely. Next, the permanent reinforcing steel and supports are installed. Finally, the concrete is placed and cured, freeing the falsework to be moved.
- In pre-cast bridges, the concrete segment is constructed on the ground, and then transported and hoisted into place. As the new segment is suspended in place by the crane, workers install steel reinforcing that attaches the new segment to preceding segments. Each segment of the bridge designed to accept connections from both preceding and succeeding segments.
- The process in step 3 is repeated until the span is completed.
- FHWA (2003). "Task 15.2 Research Synthesis Statement: Segmental Concrete Bridge Design and Construction Practices." Washington, D.C.: Federal Highway Administration. Downloaded November 2, 2005, from http://www.fhwa.dot.gov/BRIDGE/segmental/task152.htm.
- LoBuono, J. (2005). "Assembly required-The instructions for building New Jersey’s first segmental bridge." Chicago, Illinois: BridgesMagazineOnline.com. September/October. Downloaded November 2, 2005 from http://www.bridgebuildermagazine.com/.
- LoBuono, J. (2005). "Assembly required-The instructions for building New Jersey’s first segmental bridge." Chicago, Illinois: GoBridges.com. September/October. Published October 18, 2005 at http://www.gobridges.com/article.asp?id=770
- (2006) "Design & Construction of Ngong Shuen Chau Viaduct" International Conference on Bridge Engineering – Challenges in the 21st Century, Hong Kong, 1 ~ 3 November 2006 http://www.ywlgroup.com/articles.html
- (2007) "Construction of the Precast Segmental Approach - Structures for Sutong Bridge" ICE Conference 2007, Beijing http://www.ywlgroup.com/articles.html