Rib for the Eye

May 2, 2007

The reconstruction project of the Troup Howell Bridge in Rochester, N.Y., features a dramatic, context-sensitive design highlighted by a new and unique 132-m-long tri-rib arch span. Construction of the $38 million project is heading down the final stretch and the span is expected to be completed in the summer of 2007.

Edward Kraemer and Sons Inc. of Plains, Wis., was awarded the construction contract in the fall of 2003.


The reconstruction project of the Troup Howell Bridge in Rochester, N.Y., features a dramatic, context-sensitive design highlighted by a new and unique 132-m-long tri-rib arch span. Construction of the $38 million project is heading down the final stretch and the span is expected to be completed in the summer of 2007.

Edward Kraemer and Sons Inc. of Plains, Wis., was awarded the construction contract in the fall of 2003.

On the loop

With a metropolitan population of about 1.2 million, Rochester is situated on the southern shore of Lake Ontario. The Genesee River bisects the city and flows northward to the lake. An inner loop expressway surrounds the city’s central business district, which is home to international companies such as Eastman Kodak, Xerox and Bausch & Lomb. The Troup Howell Bridge carries the southern leg of the inner loop and I-490 over the river, allowing connection from suburbia to center city and from downtown to the New York State Thruway (I-90). The bridge carries 50,000 cars per day in each direction.

This bridge was originally constructed in 1954, connecting Troup Street on the west side of the river to Howell Street on the east. In 1974, it was altered to become part of the federal interstate system: The bridge was widened and the east end reconstructed to provide exit ramps to downtown.

In 1996, the New York State Department of Transportation (NYSDOT) commissioned Erdman, Anthony and Associates Inc., from Rochester, to perform an in-depth bridge inspection and structural evaluation. The results indicated that after 42 years of pounding truck traffic, the bridge had 12 leaky deck joints, a delaminated structural slab, pack rusting between piles of built-up girder flanges and fatigue cracking at partial length cover plate terminations. Given the deteriorated conditions, the vulnerable components and the ever-increasing bridge maintenance funds, NYSDOT decided it was time to replace the bridge.

The new eight-span structure is designed to be 364 m long. Although the centerpiece is a 132-m-long through-arch span crossing the Genesee River, there are four new multigirder approach spans to the west and three to the east. A two-hinged arch design over a tied arch was chosen because feedback indicated that a thinner deck was more desirable. Since extremely competent dolomite bedrock is located within 4 m from ground surface, the thrusts from the arch ribs can be transferred directly into the foundations. As a result, it was determined that a true two-hinged arch would be aesthetically pleasing as well as practical.

Arch to serve thousands

To increase the bridge’s median shoulder widths to meet current standards, further separation of the I-490 eastbound and westbound alignments was necessary. However, the amount of separation had to be kept to a minimum, owing to the presence of structures located on the edges of both approaches. Constrictions precluded the use of the common four-arch ribs arrangement, so it was decided that both bounds be supported by only three ribs. This unusual bridge is thought to be the first of its kind constructed in the U.S.

The ribs for the Troup Howell Bridge are steel boxes. The center rib is 3 m by 1.2 m and the exterior rib is 1.8 m by 1.2 m. They are spaced at 20 m. The boxes are made with a wider top flange, and its overhang geometry promotes the creation of shadows and enhances visual interest.

The arch rib bracing is Vierendeel type to maximize the view to open sky. Six brace lines connect the ribs and they are used to support expressway lighting as well. Fixtures are mounted within bottom flange penetrations at each brace.

Rather than vertical hangers, a fan-shaped orientation as seen from the elevation was chosen. A small tie (i.e., C380 x 50 or C15 x 33.9 channels oriented back to back) was added at deck level to resist the horizontal hanger component resulting from this arrangement. The tie extends from the first to last hanger and does not connect to the rib. As a result, the arch thrust will still be carried by the foundation. Subsequent to structural analysis, it was determined that the fan orientation not only provided visual interest but also was beneficial in transmitting longitudinal earthquake load from deck level back to the rib and then down to the foundation. Two structural strand hangers are provided at each of the 19 panel points for redundancy. Strand diameter varies from 38 mm (1.5 in.) to 79 mm (3.125 in.) across the span.

Elderly assists the young

One of the major construction challenges for Edward Kraemer and Sons Inc. has been to erect with staged construction. Traffic modeling indicated that a bridge closure was not an option without gridlock on city streets, so staged construction was pursued.

During the first phase of construction, the majority of new foundations beneath the existing bridge were constructed. By locating new substructure elements where none existed, more construction could be accomplished beneath the old bridge without major disruption to I-490 traffic above.

The second stage called for the demolition and replacement of the eastbound bridge. In this stage, all I-490 traffic is shifted to the westbound side, and the number of lanes is reduced from three lanes to two in each direction. Once that is completed, all I-490 traffic will be shifted to the new eastbound bridge, and the third stage of demolishing and rebuilding the westbound side will be conducted.

To erect the three arch ribs and 12 braces in stage two, the contractor creatively chose to build the new structure using the old bridge as a work platform. When erecting the ribs that straddle the eastbound, a 350-ton hydraulic crane was placed on the old eastbound deck so that all picks were made close to their respective centers of gravity. The heaviest pick weighed nearly 90 tons.

Arch ribs were temporarily supported on falsework towers prior to setting the “keystone.” To erect the northern rib and connecting braces, the contractor chose to close the bridge completely for four consecutive weekends, working from the old westbound bridge deck. I-490 through traffic was generally unaffected, since weekend counts are low and vehicles could make use of the inner loop and city streets for a short-term detour.

At this time, the eastbound bridge is complete and all traffic has been detoured to the new bridge. The old westbound bridge has been demolished and construction of the new westbound bridge has commenced. Construction is on track to be completed in the summer of 2007.

Throughout construction, residents have voiced appreciation of the bridge and eagerly await its completion.

“The Troup Howell Bridge has been a key gateway to downtown Rochester for tens of thousands of commuters and visitors who travel into the city each day,” said then-Gov. George Pataki prior to the groundbreaking in May 2004. “While improving travel for Rochester commuters and enhancing the city’s transportation infrastructure to help it remain a competitive force in attracting new businesses and jobs, we will be creating another local treasure for residents to embrace and be proud to call their own.”

About The Author: Johnson is corporate marketing coordinator at Erdman, Anthony and Associates Inc., Rochester, N.Y. She can be reached at [email protected].

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