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Extradosed Bridge Design One of a Kind on I-95 Project

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Extradosed Bridge Design One of a Kind on I-95 Project BY JAMES A. PLATOSH, P.E. CONTRIBUTING AUTHOR Extradosed bridge design one of a kind on I-95 project he replacement of the Pearl Harbor Memorial Bridge, which spans the Quinnipiac River in New Haven, Conn., will be the nation’s fi rst bridge to employ the technique of “extradosed” design—a relatively new concept that is a hybrid between a box girder Tand a conventional cable-stayed structure. The existing bridge is a girder and fl oorbeam 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 confl uence of the Quinnipiac and Mill rivers. The current structure accommodates three lanes of traffi c in each direction with no inside or outside shoulders. Ini- tially 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 Con- necticut Department of Transportation (CTDOT) identifi ed 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 de- veloped structural defi ciencies 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 fi ve 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 22 • JUNE 2008 • ROADS & BRIDGES WWW.ROADSBRIDGES.COM of the bridge will be an extradosed is lower construction costs. Since structure and no anchorage for stay cable-stayed bridge. the reinforced concrete towers of cables has to be included in the tow- The decision to use an extradosed extradosed cable-stayed bridges are ers. The low height of the towers also design was practical as well as aes- nearly one-third lower than those reduces the installation cost of stay thetic. The features that distinguish of traditional cable-stayed bridges, cables and allows them to be easily an extradosed bridge from a con- crossbeams are not necessary in the maintained or replaced as needed. ventional 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 mini- mized. 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 benefi t of the design The new bridge will have fi ve travel lanes in each direction. It will be a viaduct composed of curved steel I-girder approach structures. ROADS & BRIDGES • JUNE 2008 • 23 a The low height of the towers reduces the installation cost of stay cables and allows them to be easily maintained or replaced as needed. It also provides clear fl ight paths for the Tweed-New Haven Airport. Circle 785 26 • JUNE 2008 • ROADS & BRIDGES WWW.ROADSBRIDGES.COM a The shorter towers also provide clear fi xtures, will be used on deck wall each of the six cable blocks. For fl ight paths for the Tweed-New Ha- surfaces if concrete is used. If the security, 16 metal halide pier light- ven Airport. bridge is constructed of steel, it will ing fi xtures will be used below the be lit by a glowing surface mounted bridge deck to illuminate the lower Shining a Pearl on diffused frosted glass industrial portion of the piers and bases. Aesthetics were a major consider- fi xtures. ation in the design of the new Pearl Sixteen fi xtures on the outside of It’s all staged Harbor Memorial Bridge. Although the parapets, along with eight at the The new Q-Bridge will be built commonly referred to as the Q- pylon bases, will be used to illumi- in three stages. The fi rst half of the Bridge, it was originally built, and nate the outside of the pylon faces, bridge will be constructed along- remains, as a memorial to the losses and 11 metal halide lamps will light side and to the north of the exist- suffered in the attack that spurred U.S. entry into World War II. The design, therefore, was intended to be sophisticated and signifi cant. The bridge also serves as a gateway struc- ture to the city of New Haven, and a visually distinctive structure will take its place as one of the country’s signature bridges. The fi nal design is ASPHALT the result of a collaborative effort of a committee formed by CTDOT that The Sustainable Pavement 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 ellip- tically shaped towers rising approxi- ENERGY & RECYCLING PERFORMANCE WATER QUALITY CLEAN AIR & COOL CITIES mately 75 ft above the bridge deck. With fi ve lanes each of north- and southbound traffi c carried on sepa- Asphalt is the sustainable material rate structures, there will be a total of eight towers—four in each direc- for constructing pavements. tion. The cables of the bridge have been designed to enter cleanly into Learn more at PaveGreen.com. the towers and will be arranged par- allel to each other. From the production of the paving material, Approach pylons will visually mark to the placement of the pavement on the the beginning of the main span from road, to rehabilitation, through recycling, the approach spans. The main span asphalt pavements minimize impact on the piers on the west side of the bridge environment. Low consumption of energy also will contain a cantilevered walk- for production and construction, low emis- way that will be incorporated into sion of greenhouse gases, and conservation the city’s waterfront trail system. of natural resources help make asphalt the Both steel and concrete superstruc- ture alternatives are being designed environmental pavement of choice. for the bridge. The illumination of the bridge will • What industry is America’s number one be an important part of its aesthet- recycler? ics. For the main tower, a total of • How can asphalt pavements reduce road 16 fi xtures will be mounted on the noise? exterior of the parapets, and an ad- • What kinds of asphalt pavements can help ditional eight will be located at the manage stormwater? tower bases. The 24 fi xtures will illu- • How can asphalt pavements mitigate the minate the outside faces of the main urban heat island (UHI) effect? towers. The lighting of the span depends on whether the bridge will be con- structed of concrete or steel. Refl ec- Visit PaveGreen.com to learn more. tive material, rather than lighting Circle 753 ROADS & BRIDGES • JUNE 2008 • 27 a ing bridge. This span will carry the Park. The original boathouse has bridge and carry the new ramps to northbound lanes of I-95 when the since been demolished, along with I-91 and Rte. 34. The other two cover entire project is complete. The fi rst another building that stood at the lo- building the bridges that will carry half will carry three travel lanes in cation of the new bridge. the new ramps to I-91 and complete each direction while the existing Another diffi culty was the need to the remainder of the interchange bridge is demolished and the re- relocate two 42-in.-diam. sanitary ramps, bridges and new turnpike maining half of the new span is un- sewer lines that lay directly beneath mainline roadways. der construction. Once complete, the where part of the new bridge will be In addition to the practical benefi ts southbound lanes will be shifted to built. Construction of the new sewer the new bridge will provide—wider the second span and the bridge will lines involves slant drilling through decks, safer approaches, a smoother be opened to fi ve lanes in each direc- bedrock under the New Haven Har- fl ow of traffi c and an appealing gate- tion. Work on the new bridge will be bor. way to the New Haven area—the coordinated with the ongoing recon- Staged construction involved di- bridge will continue to serve as a struction of the massive I-91/Rte. 34 viding the corridor program into memorial. On select holidays, three interchange just west of the bridge.
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