Wish Granted

Feb. 1, 2006

The Ohio River crossing at Portsmouth built in 1927 was named to honor Ulysses Simpson Grant, the 18th president of the U.S. and general from Georgetown, Ohio, who achieved national fame as the commander-in-chief of the Union forces in the American Civil War.

The Ohio River crossing at Portsmouth built in 1927 was named to honor Ulysses Simpson Grant, the 18th president of the U.S. and general from Georgetown, Ohio, who achieved national fame as the commander-in-chief of the Union forces in the American Civil War.

The Ohio Department of Transportation acquired this 700-ft main span suspension bridge that linked Portsmouth, Ohio, and South Shore, Ky., from the Ohio Bridge Commission in 1974. Because of its age and unique design, the U.S. Grant Bridge was placed on the National Register of Historic Places, and ODOT completed two extensive renovations.

Some 70 years after its original construction, however, as population and transportation needs grew, the suspension bridge was determined to be both structurally deficient and functionally obsolete. The roadway could support only two narrow lanes leading to traffic disruptions during both regular maintenance operations and in case of a breakdown or an accident. Widening was not an economically viable option and, with mounting maintenance and rehabilitation costs, transportation authorities determined that the complete replacement of the bridge was needed.

Working with the surrounding community, ODOT’s District 9 set about formulating logistics for ensuring a design that met the functional requirements of enhanced transportation needs and the public’s expectations for aesthetics. The bridge needed to be a good fit for the site and the surroundings in addition to meeting high standards on more utilitarian aspects of transportation, serviceability and maintainability.

Because the Ohio River is heavily used for barge navigation, the goal of improved transportation also included river navigation. The tower locations of the existing 700-ft suspension bridge were not ideal for river navigation. The department, having performed due diligence on this aspect, opted for a minimum 875-ft span for the new bridge that would place the towers farther away from the channel, thus significantly improving the less-than-desirable conditions that existed with the previous channel layout.

It also was hoped that the new structure would encourage economic development, particularly in downtown Portsmouth, with traffic through the downtown area flowing smoother with a new, visually pleasing and wider bridge in place.

Priorities first

Among ODOT’s priorities was a cost-effective bridge that fit the site and met essential functional requirements, including improved transportation service, constructability, minimal maintenance and greater navigational clearances on the Ohio River. ODOT and the community also agreed that the new bridge must be aesthetically pleasing, particularly considering its prominence in the view from downtown Portsmouth. Another priority was to honor the heritage of the original bridge. ODOT salvaged unique elements of the historic bridge, including original anchorages and suspension cable, and will display these items along with descriptive information about the structure in a park adjacent to the new span.

After setting priorities for the new bridge and conducting a consultant selection process in 1999, ODOT chose two consultants to develop competing designs, one in steel and the other in concrete, to ensure competitive bids. HNTB Corp. was selected for the development of the steel option and expressed a clear understanding of the project ODOT wanted to build, had worked successfully with ODOT in the past, was well acquainted with the region and possessed broad experience with major bridge design.

Creative down, creative up

In developing the bridge alternatives for steel designs, HNTB considered four types of bridges—steel truss, steel-tied arch, suspension and cable-stayed—and developed preliminary cost estimates for each. Three-dimensional renderings and photo montages of the options also were developed for the department’s use in the public input process. Based on the type study, HNTB recommended a steel-composite, cable-stayed bridge as the most cost-effective, efficient and best-fitting solution. ODOT and the local community agreed.

Replacing the bridge in-line first meant demolition of the existing bridge and a traffic detour during the construction of the new bridge. The nearby Carl D. Perkins Bridge, named for a long-serving Kentucky congressman who also was legal counsel for that state’s Department of Highways, met the community’s needs for cross-river transportation during construction of the new span.

The demolition of the existing bridge had to be done with minimal disruption to the busy river navigation. HNTB responded with an innovative demolition procedure where the cables and the towers of the existing bridge were removed from the navigation channel within minutes.

The design specifications based on ODOT’s requirements called for a bridge with standard lanes, wide shoulders providing space for maintenance vehicles without disrupting normal traffic and future capability for additional lanes if traffic demand grew more than the projected levels. Design features of the new U.S. Grant Bridge are the following:

  • Two 12-ft lanes and two 12-ft shoulders able to carry 125% of the legal load. The new bridge will permit simultaneous maintenance and traffic, potential expansion to four lanes of traffic and pedestrian traffic. ODOT expects the bridge will support more than 16,000 vehicles daily within 15 years;
  • The main span is 875 ft long with end spans of 350 ft and 460 ft. The entire bridge, including approach spans, is 2,155 ft long;
  • The bridge’s main span has a 55-ft vertical clearance for river traffic. The design also expanded horizontal clearance to 850 ft to address the navigability concerns of river pilots by moving the support tower locations on each side of the river far closer to the shorelines—125 ft closer to Kentucky and 50 ft closer to Ohio;
  • The towers are designed to withstand 6.5 million lb of force due to accidental barge impacts. The tower design was further complicated by a 50-ft variation of river flow elevation at this location. This wide variation in river elevation meant that ship impact loads had to be applied at a relatively high elevation on the tower while avoiding any features that may become hidden obstructions within 12 ft of the waterline per U.S. Coast Guard (USCG) requirements; and
  • ODOT asked for an aesthetic lighting design that highlights the new bridge’s visual features.
In addition to the above primary design requirements, several other issues complicated the design process. First, the site constraints dictated a span layout that is not symmetrical, which meant paying more attention to the engineering of the bridge so it would not overstress the towers and the superstructure during the bridge construction.

The department’s decision to place the new bridge on the original alignment was to minimize right-of-way issues, which was an important consideration for both saving time and money in sync with the overall goal of achieving the most cost-effective replacement structure. There was some effort to see if the old abutment on the Ohio side could be reused in some way, but this was not found to be practical.

HNTB kept the department’s objectives for an efficient and aesthetically pleasing bridge at the forefront when developing the final plans. The costs of the deep foundations and towers are a substantial part of the cost of a major bridge, and careful design of these items is key to the overall cost efficiency of the bridge.

At the new U.S. Grant Bridge, the high-water elevations meant that conventional foundations would require extremely deep cofferdams during construction, which would have increased both the cost and the risk. Recognizing this requirement, HNTB developed a compact foundation design that can be built basically from a barge, yet sufficiently strong for supporting the tower loads and the large ship impact loads. The USCG requirement that there be no elements that could become hidden submerged obstructions led to the unique lower tower shape. The compact towers support the cables at a special anchor head at the very top of the tower, thereby increasing the efficiency of cables in resisting the loads as well as improving the speed of tower construction with respect to conventional designs where the tower shaft is interrupted by cable penetrations along its height.

The design efficiency of the superstructure is evident from the use of only 35 lb of structural steel per sq ft of the bridge area with a design that meets a higher level of performance than typical in the industry. The special post-tensioned concrete deck slab is designed for practically no tensile stresses on the top surface of the slab, whereas conventional designs allow typically about 200- to 250-psi tension depending on concrete strength. ODOT’s emphasis on maintainability is further reflected in HNTB’s design by using an integral abutment at the Ohio side, using only one expansion joint for the entire bridge and minimizing the number of bearings by framing the superstructure to the towers.

The constructability and design efficiency of the steel-composite bridge proved evident when all five contractors who responded to ODOT’s letting chose to bid the steel alternative only. HNTB, working closely with ODOT, successfully managed the competing requirements and constraints of the project to formulate the best overall solution. ODOT awarded the construction contract on April 20, 2001.

Super completion

Quick out of the gate, construction began less than two months later. The new U.S. Grant Bridge comprises 20,000 ft—almost four miles—of stay cables; 1,900 tons of structural steel (in the superstructure and towers) and another 1,675 tons of reinforcing steel; and 9,000 cu yd of concrete.

But construction is never as easy as planning. Despite the standard sampling of conditions at the site, several differing situations in the Ohio River were discovered after the project got under way. Weather caused other delays. A major ice storm in February 2003 and higher-than-expected river levels due to heavier rains than anticipated prevented the contractor from working on the foundations. One of the contractor’s barge cranes also sank in the river.

Despite weather and other challenges that could have prevented completion of the new bridge, ODOT and the contractor, CJ Mahan of Ohio, worked closely together to complete the bridge’s superstructure by the end of 2005. One of ODOT’s time-saving initiatives was to sponsor the development of a shop-fabricated steel embedment for the cable anchorage assembly in the tower instead of the original in-situ formed concrete design. HNTB developed the steel anchorage design for ODOT, and the design ultimately proved quite successful.

Replacing a historic structure is never a straightforward task, and the U.S. Grant Bridge project at Portsmouth is no exception to the rule. However, with ODOT working closely with the affected communities, HNTB and CJ Mahan, a proficient new structure befitting its namesake is nearing completion. With careful attention to the unique needs of Ohioans, ODOT paved the way for an innovative, efficient and cost-effective new bridge that will become Ohio’s first major cable-stayed bridge.

About The Author: Kumarasena is an associate vice president and manager of complex structures in HNTB’s Boston office.

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