By: James A. Platosh, P.E.
The replacement of the Pearl Harbor Memorial Bridge, which spans the Quinnipiac River in New Haven, Conn., will be the nation’s first bridge to employ the technique of “extradosed” design—a relatively new concept that is a hybrid between a box girder and a conventional cable-stayed structure.
The existing bridge is a girder and floorbeam design, in which steel beams support the concrete bridge deck.
Known locally as the Q-Bridge (for Quinnipiac), the new structure will replace the original span, which opened in 1958. The replacement bridge, which is scheduled for completion in 2016, is the centerpiece of a $2 billion program to reconstruct and widen 13 miles of I-95 between West Haven and Branford. The overall project is part of the New Haven Harbor Crossing Corridor Improvement Program, one of the largest, most comprehensive transportation programs ever undertaken in Connecticut.
The Q-Bridge carries I-95 over New Haven Harbor at the confluence of the Quinnipiac and Mill rivers. The current structure accommodates three lanes of traffic in each direction with no inside or outside shoulders. Initially designed to handle 40,000 vehicles a day, it now carries more than 60,000, and its volume is expected to increase to 140,000 by 2015. The Connecticut Department of Transportation (CTDOT) identified the area through which the bridge passes as the largest bottleneck in the state.
Excessive volume is not the only problem. The existing bridge has developed structural deficiencies over the years, and its lack of redundant critical elements fails to minimize its chance of failure. CTDOT, the Federal Highway Administration and local municipalities all have cited the need for operational and safety upgrades to the I-95 corridor through the affected area.
Extra dose of design
The new bridge will have five travel lanes in each direction, full-width inside and outside shoulders, a new median barrier and improved ramp geometry. Its unique feature will be its breakthrough design. It will be a viaduct composed of curved steel I-girder approach structures and a main span that will have a combined length of more than a mile. The main span of the bridge will be an extradosed cable-stayed bridge.
The decision to use an extradosed design was practical as well as aesthetic. The features that distinguish an extradosed bridge from a conventional cable-stayed structure are lower tower heights, which give a smaller angle of inclination to the stay cables and a structure depth that is greater than that of a cable-stayed superstructure. These factors were critical, because with a nearby airport and an active waterway the tower heights needed to be minimized. In the new design, the wire-carrying cables will be placed outside the girders and on the main concrete towers as opposed to higher up on tall towers, which would have been necessary with a cable-stayed bridge. Both the girders and the wire cables will carry the loads, and the bridge will have a longer span than that of a conventional bridge.
An additional benefit of the design is lower construction costs. Since the reinforced concrete towers of extradosed cable-stayed bridges are nearly one-third lower than those of traditional cable-stayed bridges, crossbeams are not necessary in the structure and no anchorage for stay cables has to be included in the towers. The low height of the towers also reduces the installation cost of stay cables and allows them to be easily maintained or replaced as needed. The shorter towers also provide clear flight paths for the Tweed-New Haven Airport.
Shining a Pearl
Aesthetics were a major consideration in the design of the new Pearl Harbor Memorial Bridge. Although commonly referred to as the Q-Bridge, it was originally built, and remains, as a memorial to the losses suffered in the attack that spurred U.S. entry into World War II. The design, therefore, was intended to be sophisticated and significant. The bridge also serves as a gateway structure to the city of New Haven, and a visually distinctive structure will take its place as one of the country’s signature bridges. The final design is the result of a collaborative effort of a committee formed by CTDOT that also includes the FHWA and URS as well as members of the Connecticut division of the American Institute of Architects and representatives of the city of New Haven.
The new bridge will feature elliptically shaped towers rising approximately 75 ft above the bridge deck. With five lanes each of north- and southbound traffic carried on separate structures, there will be a total of eight towers—four in each direction. The cables of the bridge have been designed to enter cleanly into the towers and will be arranged parallel to each other.
Approach pylons will visually mark the beginning of the main span from the approach spans. The main span piers on the west side of the bridge also will contain a cantilevered walkway that will be incorporated into the city’s waterfront trail system. Both steel and concrete superstructure alternatives are being designed for the bridge.
The illumination of the bridge will be an important part of its aesthetics. For the main tower, a total of 16 fixtures will be mounted on the exterior of the parapets, and an additional eight will be located at the tower bases. The 24 fixtures will illuminate the outside faces of the main towers.
The lighting of the span depends on whether the bridge will be constructed of concrete or steel. Reflective material, rather than lighting fixtures, will be used on deck wall surfaces if concrete is used. If the bridge is constructed of steel, it will be lit by a glowing surface mounted on diffused frosted glass industrial fixtures.
Sixteen fixtures on the outside of the parapets, along with eight at the pylon bases, will be used to illuminate the outside of the pylon faces, and 11 metal halide lamps will light each of the six cable blocks. For security, 16 metal halide pier lighting fixtures will be used below the bridge deck to illuminate the lower portion of the piers and bases.
It’s all staged
The new Q-Bridge will be built in three stages. The first half of the bridge will be constructed alongside and to the north of the existing bridge. This span will carry the northbound lanes of I-95 when the entire project is complete. The first half will carry three travel lanes in each direction while the existing bridge is demolished and the remaining half of the new span is under construction. Once complete, the southbound lanes will be shifted to the second span and the bridge will be opened to five lanes in each direction. Work on the new bridge will be coordinated with the ongoing reconstruction of the massive I-91/Rte. 34 interchange just west of the bridge.
Construction on elements other than the bridge—such as approaches and removal of some buildings—has been proceeding apace, but there have been controversies to resolve and obstacles to overcome. One was the discovery that the former Yale Boathouse, a historically significant structure, sat directly in the path of the new bridge. The city of New Haven demanded that the structure be preserved, and after discussion and negotiation, CTDOT agreed to build a replica boathouse at Long Wharf Park. The original boathouse has since been demolished, along with another building that stood at the location of the new bridge.
Another difficulty was the need to relocate two 42-in.-diam. sanitary sewer lines that lay directly beneath where part of the new bridge will be built. Construction of the new sewer lines involves slant drilling through bedrock under the New Haven Harbor.
Staged construction involved dividing the corridor program into multiple contracts. The eastern approach to the bridge was reconstructed and widened through two separate contracts. The first involved the approach through East Haven, while the second covered the reconstruction of I-95 from the East Haven/New Haven border to the eastern abutment of the bridge.
The reconstruction of the western approach was split into three contracts. The first, already completed, involved the construction of earthworks that will eventually support the western abutment of the new bridge and carry the new ramps to I-91 and Rte. 34. The other two cover building the bridges that will carry the new ramps to I-91 and complete the remainder of the interchange ramps, bridges and new turnpike mainline roadways.
In addition to the practical benefits the new bridge will provide—wider decks, safer approaches, a smoother flow of traffic and an appealing gateway to the New Haven area—the bridge will continue to serve as a memorial. On select holidays, three Xenon lamp beam tracker lights at each of the two towers will point up toward the sky in memory of the fallen.
About The Author: Platosh is a project manager for URS Corp., Rocky Hill, Conn.
