Main Street Bridge (Columbus)

Main Street Bridge
New Main Street Bridge (near completion) Viewed from the south, Downtown, Columbus, Ohio
Official name	Main Street Bridge
Carries	three one-way general purpose lanes, one pedestrian
Crosses	Scioto River
Locale	Columbus, Ohio
Maintained by	Ohio Department of Transportation
ID number	2503212
Design	inclined arch
Total length	700 feet (215 m)
Width	~65 feet (20 m)
Longest span	400 feet (122 m)
Construction begin	2006
Construction end	July 2010
Opened	July 30, 2010
Coordinates	39°57′22″N 83°00′25″W / 39.956°N 83.007°W / 39.956; -83.007Coordinates: 39°57′22″N 83°00′25″W / 39.956°N 83.007°W / 39.956; -83.007

The Main Street Bridge in Columbus, Ohio is a 700 ft (210 m), three-span, inclined arch suspension bridge over the Scioto River. The bridge is the first in North America and only the fifth in the world to use an inclined arch superstructure.^[1] The final cost for the bridge was $60.1 million USD.^[2]

History

1937 Bridge in foreground

The original Main Street bridge was a multiple-span, art-deco open-spandrel concrete deck arch bridge, built in 1937. After years of degradation due to weather and traffic, the bridge was deemed unfit for use and closed in 2000.^{[3][dead link]}

Wanting an iconic structure to replace the old bridge, the city of Columbus contracted Dr. Spiro Pollalis, professor of design technology and management at the Harvard University Graduate School of Design to design the bridge. His design, altered slightly for budget reasons, was opened for traffic on July 30, 2010.^[3]

Design

Arch

The original concept design of the Main Street bridge was far more complicated and costly than the final design. Initially, the bridge called for a very shallow 10:1 span-to-rise ratio for the main arch, creating significant axial and bending forces. To accommodate the excess forces, the design called for expensive, high-strength concrete and steel to support the bridge. Because of the high cost of materials and construction of such a span, the design of the arch was revised to a 6.6:1 span-to-rise ratio, making the main arch taller as well as shortening it from 480 ft (150 m) to 400 ft (120 m). This design change is expected to allow for cheaper materials and save over 60,000 pounds (27,000 kg) of steel while keeping the 10 degree incline that makes the bridge so unique.^[4]

Bridge deck

The bridge deck is composed of two separate decks, a 35 foot (10.7 m) wide vehicular deck carrying three lanes of eastbound traffic, and a 18 foot (5.5 m) wide pedestrian deck elevated above the vehicular deck.^[1] While the redesign of the original concept altered the deck supports, the actual construction of the decks was only changed slightly to accommodate the new design.^[4]

L-struts

The Main Street bridge also calls for thirteen l-struts, which will attach the arch to the bridge deck. Their original design used tapering geometries which changed depending on the strut, creating thirteen distinct struts that needed to be designed and tested separately. This made the struts very costly, and designers had to simplify the design to fit within budget. The l-struts on the current design are more uniform steel members, which will cost much less to construct. While the aesthetics of the original design have changed, the new l-struts are supposed to be similarly appealing. The redesign is also expected to save over 400,000 pounds of steel from the struts.^[4]

Piers

The final redesign of the Main street bridge was of the piers. Originally, the design called for two 'V-piers', formed by the convergence of the main arch and the secondary arches on either side. This design proved to be nearly impossible to make structurally sound, and engineers had to simplify the piers. To do so they created a 'crescent pier' shape, which removes the two smaller arches on either end and creates a larger pier to provide better support.^[4]

References

1. ^ ^{a b} "Main Street Bridge Replacement: Steel Structure Makes Dramatic Visual Impact on Downtown Columbus Skyline". Downtown Columbus. http://www.downtowncolumbus.com/progress/main-street-bridge. Retrieved 2010-08-06. 
2. ^ "Main Street bridge opened to traffic". The Columbus Dispatch. http://www.dispatch.com/live/content/local_news/stories/2010/07/30/main-street-bridge-to-open.html?sid=101. Retrieved 2010-08-06. 
3. ^ ^{a b} "Main Street Bridge". Franklin County. http://www.franklincountyohio.gov/probate/PDF/MAIN%20STREET%20BRIDGE.pdf. Retrieved 2010-08-06. 
4. ^ ^{a b c d} "The Main Street Bridge Replacement". Genesis Structures, Inc.. http://www.genesisstructures.com/papers/TRB_Paper_Main%20Street_ver4.PDF. Retrieved 2007-11-13.