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).[1]
These bridges are very economical for long spans (more than 100 metres or 330 feet), especially when access to the construction site is restricted. They are also chosen for their aesthetic appeal.
History
The first cantilevered segmental cast-in-place concrete bridge, built in 1930, was Ponte Emílio Baumgart [de] across Rio do Peixe in the state of Santa Catarina of Brazil.[2] It was followed in 1951 by the prestressed concrete bridge across the Lahn River in Balduinstein, Germany [de], the first of many cantilevered bridges designed by Ulrich Finsterwalder [de].[3]
The first prestressed concrete bridge, assembled by several precast elements, was the Pont de Luzancy [fr] across the river Marne in France, built according to the design by Eugène Freyssinet and commenced in 1940, but due to the war, completed only in 1946.
Construction
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 principal 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 atop 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. This process is usually accomplished using a self propelled bridge layer that hoists the bridge section into place.
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 is designed to accept connections from both preceding and succeeding segments.
The process in step 3 is repeated until the span is completed.
^Ulrich Finsterwalder. The first prestressed concrete free cantilever bridge was the Lahn Bridge near Balduinstein (1950), which was followed in 1952 by the Nibelungen Bridge in Worms with a maximum span of 132 meters. [1]
(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
