The Main Street Bridge in Columbus

Columbus, Ohio

Columbus is the capital of and the largest city in the U.S. state of Ohio. The broader metropolitan area encompasses several counties and is the third largest in Ohio behind those of Cleveland and Cincinnati. Columbus is the third largest city in the American Midwest, and the fifteenth largest city...

, Ohio

Ohio

Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...

 is a 700 ft (213.4 m), three-span, inclined arch

Arch bridge

An arch bridge is a bridge with abutments at each end shaped as a curved arch. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side...

 suspension bridge over the Scioto River

Scioto River

The Scioto River is a river in central and southern Ohio more than 231 miles in length. It rises in Auglaize County in west central Ohio, flows through Columbus, Ohio, where it collects its largest tributary, the Olentangy River, and meets the Ohio River at Portsmouth...

. The bridge is the first in North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and only the fifth in the world to use an inclined arch superstructure. The final cost for the bridge was $60.1 million USD.

History

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.

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.

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 (146.3 m) to 400 ft (121.9 m). This design change is expected to allow for cheaper materials and save over 60000 pounds (27,215.5 kg) of steel while keeping the 10 degree incline that makes the bridge so unique.

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. 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.

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.

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.