Clark Bridge

Details
Location: Alton, Ill.
Service: Primary design consultants
Project Cost: $92 million
Client/Owner: Illinois Department of Transportation
Completed: 1994

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Description
Challenges
Disciplines involved
Design concepts
Awards

Description
The Illinois Department of Transportation (IDOT) retained Hanson as the primary design consultant for the Clark Bridge, a 4,620-foot-long structure. The original Clark Bridge was built in 1928. The new Clark Bridge needed to accommodate traffic movements between Alton, Ill., and North St. Charles County, Mo., on U.S. Route 67.

The IDOT assignment called for the development of plans for both steel and concrete versions of the bridge. Hanson coordinated the project with IDOT as lead agency and the Missouri Department of Transportation, the U.S. Army Corps of Engineers and the U.S. Coast Guard as participating agencies. Hanson retained Figg and Muller Engineers as technical consultants to provide the plans for the concrete version.

The project included the following phases:

• bridge type and study,
• type, size and location study, and
• final plans and construction review.

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Challenges
One challenge to Hanson's engineers involved designing a new, safe and efficient bridge crossing over the Mississippi River that could accommodate 20,000 cars a day traveling between Alton, Ill., and North St. Charles County, Mo., on U.S. Route 67. Hanson's team worked to prevent disruption to the river's navigation during construction and dealt with construction delays during the catastrophic Great Flood of 1993.

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Disciplines involved
Hanson completed the preliminary geotechnical report and borings in 1985. In 1988, the firm began the final geotechnical investigation and preliminary design for the bridge. By 1990, the final designs were complete and construction was begun. Although the flood of 1993 greatly affected the Alton area, the bridge opening was not too delayed. It was dedicated and opened to traffic in January 1994.

Throughout the project, Hanson provided structural, transportation, geotechnical and hydraulic engineering, and technical support during construction. The project included plan preparation for rail corridor realignment, building demolition, bridge demolition and bridge lighting. Hanson also provided review of about 1,000 shop drawings and approximately 400 additional contractor documents.

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Design concepts
While single pylons have been used on other bridges, the combination of a dual plane of cable stays supported by single pylons had never been used in the United States. The single pylons with supporting piers reduce the obstruction to the skewed navigation channel.

A top-mounted common saddle provides for continuous stays, reduces the number of expensive anchor stays and eliminates the splitting (tensile) forces in the concrete pylon that non-continuous stays would have imposed. Using a common saddle mounted at the top of the pylon improves the efficiency of the stays by maximizing the stays' slope relative to the deck.

The dual sloping planes of stays provide an efficient method for torsionally stabilizing the slab-and-girder floor system. In cross section, the stays, the pylon and the deck form a series of triangles, a stable configuration that engineers have used for centuries.

Using a balanced cantilever method for the main spans resulted in less interruption to river traffic during construction. The sloping planes of stays and the single pylon provided a beautiful structure, while the common saddle for the stays allowed for easier stay placement.

The cable-stay system uses basic components originally developed for the post-tensioning industry but improved for application to cable-stay technology. The seven-wire strand used on the Clark Bridge are epoxy coated for corrosion protection.

The precast, post-tensioned deck panels allowed the contractor to erect the main unit superstructure in just 10 months. They also reduced the creep and shrinkage of the concrete deck on the structure. Post-tensioning created continuity in the deck and reduced concrete tensile stresses during construction.

The approaches use conventional steel-plate girders made composite with a cast-in-place concrete slab. This design optimized the span lengths, girder spacing, girder depth and slab thickness.

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Awards
Recognized for its beauty, function and economic impact, the Clark Bridge has received several awards, including:

• Federal Design Achievement Award - The National Endowment for the Arts and the U.S. General Services Administration;
• Engineering Excellence Honor Award - American Consulting Engineers Council
• Prize Bridge Award - American Institute of Steel Construction
• Eminent Conceptor Award - Consulting Engineers Council of Illinois
• Outstanding Civil Engineering Achievement Award - St. Louis Section of the American Society of Civil Engineers
• Build America Award, New Heavy Industrial Division - the Associated General Contractors of America
• Twelve Best Bridges - Consulting Engineers Magazine

In addition to these awards, the Clark Bridge was featured in a two-part documentary series, "Super Bridge," produced from the Public Broadcasting Service program NOVA.

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