Segmental bridge


Segmental bridge

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.

History

The first segmental concrete bridge, built in 1950, was cast-in-place across the Lahn River in Balduinstein, Germany.Fact|date=August 2007

The first precast segmental concrete bridge, built in 1962, crossed the Seine River in France. [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.]

The first U.S. precast segmental concrete bridge, built in 1973, was built in Corpus Christi, Texas. [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/.]

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.

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 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.

Notable examples

*Chesapeake and Delaware Canal Bridge in Delaware is a cable-stayed bridge using precast concrete segments for the approach and center spans
*Linn Cove Viaduct in the Blue Ridge Mountains, North Carolina (precast)
*Manwel Dimech Bridge in St. Julian's (San Ġiljan), Malta. This bridge connects the two parts of Regional Road and pass over Għomar Valley.
*Seven Mile Bridge in the Florida Keys (precast)
*The Interstate H-3 viaducts through the Ko'olau Mountains, Oahu, Hawaii (CIP Segmental)
*The new Pennsylvania Turnpike (I-76) bridges over the Susquehanna River south of Harrisburg, Pennsylvania (precast)
*The Eastern span replacement of the San Francisco-Oakland Bay Bridge viaduct (precast)
*The Benicia-Martinez Bridge (northbound span) between Benicia and Martinez, CA (CIP Segmental)
*The Four Bears Bridge over the Missouri River in North Dakota utilizes precast concrete segments, erected with the balanced cantilever method (precast)
*The High Five Interchange connecting US-75 and I-635 in Dallas, TX (precast)
*The AirTrain linking NY's Kennedy International Airport with the Jamaica Transit Center
*The ramps leading between the Brooklyn Queens Expressway (NY I-278) and the Williamsburgh Bridge (connecting to Manhattan)

References

Further reading

# 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

Related sites

*http://www.fhwa.dot.gov/bridge/segmental/index.htm
*http://www.asbi-assoc.org/
*http://www.pbworld.com/news_events/publications/network/issue_57/57_03_murilloj_briefhistoryseg.asp
*http://www.pbworld.com/news_events/publications/network/issue_28/28_16_wahlp_constructionsequence.asp
*http://www.polito.it/creepanalysis


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