First-Place Area Steel Bridges

Two steel bridges in New York state and one in Pennsylvania recently took first place in their respective categories in a competition sponsored by the National Steel Bridge Alliance (Chicago).

The competition honored significant steel bridges constructed within the U.S between June 2003 and

June 2005. In evaluating projects for these awards, the jury considered such characteristics as innovative design and construction, aesthetics and economy. The Alliance presented these awards at its World Steel Bridge Symposium, held in early December of last year.

Movable span: Patrick O'Rorke Bridge

The $104-million O'Rorke bridge serves as a focal point in the revitalization of the Port of Rochester, N.Y., connecting the communities on either side of the Genesee River. The new bridge has a 243-foot long Scherzer rolling-lift bascule main span. This movable span is flanked by a 148-foot-long, single-span steel girder approach structure on the west side and a 530-foot long, three-span curved and splayed steel girder approach structure on the east side. The new bridge is 22 feet higher than its predecessor, carrying four 11-foot-wide travel lanes, two 5-foot-wide bicycle lanes and oversized 7-foot-wide sidewalks.

Designers chose steel as the primary structural material for its strength, depth and length requirements of the main spans, and its ability to easily conform to the shapes needed for aesthetics. The project required more than 2,600 tons of structural steel, five miles of H and pipe piles, and 1.8 million pounds of reinforcement.

The east and west bascule piers rest on different geological site conditions. To deal with deep overburden on the eastern side, this pier is founded on 114 HP 14 by 117 steel piles, with an average length of 100 feet. The original design for the western side assumed a rock slope of about 13 degrees, but during initial site work the contractor discovered that the rock slope was actually 33 degrees. All parties cooperated on a revised design, developing an alternate drilled shaft foundation to address constructability, safety and cost concerns. Installed foundations at the west bascule pier consist of a 3-by-8 grid of 53-inch diameter shafts with permanent steel casings and 48-inch diameter rock sockets. Drilled shaft lengths vary from 30 feet to 60 feet.

Contract provisions prohibited construction activities that blocked the navigation channel for extended periods of time. To erect the structural steel for the toe-end of the bascule leaves, the contractor opted to place a 500-ton hydraulic crane on the concrete deck of the flanking approach structures rather than on a barge. To avoid deck damage, the lift plan used a combination of temporary shoring and heavy steel grillages under the crane outriggers. The O'Rorke bridge opened in the autumn of 2004.

Owner: New York State Department of Transportation

Designer, prime consultant: Bergmann Associates

Designer: URS Corporation

General contractor: Crane-Hogan Structural Systems, Inc.

Steel detailer: Tensor Engineering

Steel fabricator: PDM Bridge

Medium Span: New Croton Dam Spillway Bridge

The 200-foot, $4.6-million steel-deck arch bridge over the New Croton Dam Spillway provides a dramatic focal point for the monumental dam in time for its 100th anniversary. Constructed in fast-track fashion, the replacement bridge achieves an aesthetic improvement over the existing bridge built in 1975.

Designers chose structural steel for this project, taking into account early history, aesthetics and durability. The new bridge represents an improved and more durable version of the original bridge built in 1905. Modern materials and current design standards maximize service life and minimize maintenance.

The new steel superstructure includes 2-foot by 3-foot welded box sections for the ribs, welded steel box sections with integral connection plates at the spandrel columns and spandrel girders, a rolled steel beam floorbeam/stringer system, and sealed structural tubes bracing elements at the columns and arch ribs.

Fabricators made the new arch ribs in three sections with bolted field splices for easy and cost-effective erection. The ribs bear on the existing granite skewbacks outboard of the 1975 bridge arches at the location where the 1905 bridge was seated.

To avoid deterioration caused by the misty spray of the spillway, all structural detailing aims at minimizing corrosion. The visible finish coat of all steel is a highly durable thermally sprayed metalizing. Inaccessible interiors of structural tubes are coated by hot dip galvanizing. The new bridge seats and deck incorporate high performance concrete and solid stainless steel reinforcing for maximum service life.

A key to success of the construction phase was the contractor's innovative overall erection plan. Erectors first built temporary columns to support the existing deck girders. They removed some deck girders to expedite construction of new bridge seats. The contractor decided to use the existing arches to support the new arch segments being erected. Later, the new arches supported disassembly of the old ones. Erectors constructed the new arch ribs in segments, using cranes from both ends of the bridge. Workers bolted the splices and grouted the bases to prepare the ribs for carrying load. The contractor completed the bridge on time in December of 2004.

Owner: New York City Dept. of Environmental Protection

Designer: Hardesty & Hanover, LLP

General contractor and erector: Kiewit Constructors, Inc.

Steel detailer: Tensor Engineering

Steel fabricator: High Steel Structures, Inc.

Short Span: Germantown Avenue Bridge

Replacement of a nine-span straight bridge over Wissahickon Creek with a 50 percent longer three-span curved steel girder bridge solves several engineering challenges and results in an attractive structure. Fewer piers for the new 313-foot bridge in the upscale Chestnut Hill section of Philadelphia offer a wider hydraulic opening. The wider opening, along with the shallow steel superstructure depth of the bridge, reduces upstream flooding and local scouring.

The new curved roadway eliminates a hazardous 15-mph bend and permits a consistent 35-mph speed throughout this urban arterial roadway. Use of real and formed stone surfaces, old-style pedestal streetlights, and ornamental railings helps integrate the bridge into its surroundings. All seven of the designated interested community groups considered the final design a resounding success.

The bridge has sidewalks on both the upstream and downstream sides. The upstream sidewalk and roadway form one bridge superstructure. The downstream pedestrian sidewalk rests on a separate superstructure that pulls away from the main bridge, providing a direct path to a park entrance for hikers, bicyclists and equestrians.

After erection of the steel girders for the downstream pedestrian bridge, the contractor detected excessive lateral movement from horizontal forces. To dampen this movement, the designer suggested that a "soft-tie," similar to a steering strut on an automobile, be placed between the two superstructures. The tie provides lateral restraint to the downstream pedestrian bridge without transmitting live load deflections or vibrations from the vehicular bridge.

Hundreds of local residents, political dignitaries and religious leaders gathered for a grand opening of the bridge in late October 2003. A community celebration sponsored by Chestnut Hill College hailed the project as a significant contribution to the community.

Owner: City of Philadelphia

Designer: URS Corporation

Contractor: Neshaminy Constructors, Inc.

Steel detailer, fabricator and erector: High Steel Structures, Inc.