Extradosed bridge design one of a kind on I-95 ... - Roads & Bridges

BY JAMES A. PLATOSH, P.E.CONTRIBUTING AUTHOR<strong>Extradosed</strong> <strong>bridge</strong> <strong>design</strong><strong>one</strong> <strong>of</strong> a <strong>kind</strong> on I-95 projectThe replacement <strong>of</strong> the Pearl Harbor Memorial Bridge, which spans the QuinnipiacRiver in New Haven, Conn., will be the nation’s first <strong>bridge</strong> to employ the technique <strong>of</strong>“extradosed” <strong>design</strong>—a relatively new concept that is a hybrid between a box girderand a conventional cable-stayed structure.The existing <strong>bridge</strong> is a girder and floorbeam <strong>design</strong>, in which steel beamssupport the concrete <strong>bridge</strong> deck.Known locally as the Q-Bridge (for Quinnipiac), the new structure willreplace the original span, which opened in 1958. The replacement <strong>bridge</strong>,which is scheduled for completion in 2016, is the centerpiece <strong>of</strong> a $2 billionprogram to reconstruct and widen 13 miles <strong>of</strong> I-95 between West Havenand Branford. The overall project is part <strong>of</strong> the New Haven Harbor CrossingCorridor Improvement Program, <strong>one</strong> <strong>of</strong> the largest, most comprehensivetransportation programs ever undertaken in Connecticut.The Q-Bridge carries I-95 over New Haven Harbor at the confluence <strong>of</strong>the Quinnipiac and Mill rivers. The current structure accommodates threelanes <strong>of</strong> traffic in each direction with no inside or outside shoulders. Initially<strong>design</strong>ed to handle 40,000 vehicles a day, it now carries more than60,000, and its volume is expected to increase to 140,000 by 2015. The ConnecticutDepartment <strong>of</strong> Transportation (CTDOT) identified the area throughwhich the <strong>bridge</strong> passes as the largest bottleneck in the state.Excessive volume is not the only problem. The existing <strong>bridge</strong> has developedstructural deficiencies over the years, and its lack <strong>of</strong> redundantcritical elements fails to minimize its chance <strong>of</strong> failure. CTDOT, the FederalHighway Administration and local municipalities all have cited the need foroperational and safety upgrades to the I-95 corridor through the affectedarea.Extra dose <strong>of</strong> <strong>design</strong>The new <strong>bridge</strong> will have five travel lanes in each direction, full-widthinside and outside shoulders, a new median barrier and improved rampgeometry. Its unique feature will be its breakthrough <strong>design</strong>. It will be aviaduct composed <strong>of</strong> curved steel I-girder approach structures and a mainspan that will have a combined length <strong>of</strong> more than a mile. The main span22• JUNE 2008 • ROADS & BRIDGES WWW.ROADSBRIDGES.COM

<strong>of</strong> the <strong>bridge</strong> will be an extradosedcable-stayed <strong>bridge</strong>.The decision to use an extradosed<strong>design</strong> was practical as well as aesthetic.The features that distinguishan extradosed <strong>bridge</strong> from a conventionalcable-stayed structure arelower tower heights, which give asmaller angle <strong>of</strong> inclination to thestay cables and a structure depththat is greater than that <strong>of</strong> a cablestayedsuperstructure. These factorswere critical, because with a nearbyairport and an active waterway thetower heights needed to be minimized.In the new <strong>design</strong>, the wirecarryingcables will be placed outsidethe girders and on the main concretetowers as opposed to higher up ontall towers, which would have beennecessary with a cable-stayed <strong>bridge</strong>.Both the girders and the wire cableswill carry the loads, and the <strong>bridge</strong>will have a longer span than that <strong>of</strong> aconventional <strong>bridge</strong>.An additional benefit <strong>of</strong> the <strong>design</strong>is lower construction costs. Sincethe reinforced concrete towers <strong>of</strong>extradosed cable-stayed <strong>bridge</strong>s arenearly <strong>one</strong>-third lower than those<strong>of</strong> traditional cable-stayed <strong>bridge</strong>s,crossbeams are not necessary in thestructure and no anchorage for staycables has to be included in the towers.The low height <strong>of</strong> the towers alsoreduces the installation cost <strong>of</strong> staycables and allows them to be easilymaintained or replaced as needed.The new <strong>bridge</strong> will have five travel lanes in each direction. It will be aviaduct composed <strong>of</strong> curved steel I-girder approach structures.ROADS & BRIDGES • JUNE 2008 •23

aThe low height <strong>of</strong> the towers reduces the installation cost <strong>of</strong> stay cables and allows them to be easilymaintained or replaced as needed. It also provides clear flight paths for the Tweed-New Haven Airport.26Circle 785• JUNE 2008 • ROADS & BRIDGES WWW.ROADSBRIDGES.COM

aThe shorter towers also provide clearflight paths for the Tweed-New HavenAirport.Shining a PearlAesthetics were a major considerationin the <strong>design</strong> <strong>of</strong> the new PearlHarbor Memorial Bridge. Althoughcommonly referred to as the Q-Bridge, it was originally built, andremains, as a memorial to the lossessuffered in the attack that spurredU.S. entry into World War II. The<strong>design</strong>, therefore, was intended tobe sophisticated and significant. The<strong>bridge</strong> also serves as a gateway structureto the city <strong>of</strong> New Haven, anda visually distinctive structure willtake its place as <strong>one</strong> <strong>of</strong> the country’ssignature <strong>bridge</strong>s. The final <strong>design</strong> isthe result <strong>of</strong> a collaborative effort <strong>of</strong>a committee formed by CTDOT thatalso includes the FHWA and URS aswell as members <strong>of</strong> the Connecticutdivision <strong>of</strong> the American Institute <strong>of</strong>Architects and representatives <strong>of</strong> thecity <strong>of</strong> New Haven.The new <strong>bridge</strong> will feature ellipticallyshaped towers rising approximately75 ft above the <strong>bridge</strong> deck.With five lanes each <strong>of</strong> north- andsouthbound traffic carried on separatestructures, there will be a total<strong>of</strong> eight towers—four in each direction.The cables <strong>of</strong> the <strong>bridge</strong> havebeen <strong>design</strong>ed to enter cleanly intothe towers and will be arranged parallelto each other.Approach pylons will visually markthe beginning <strong>of</strong> the main span fromthe approach spans. The main spanpiers on the west side <strong>of</strong> the <strong>bridge</strong>also will contain a cantilevered walkwaythat will be incorporated intothe city’s waterfront trail system.Both steel and concrete superstructurealternatives are being <strong>design</strong>edfor the <strong>bridge</strong>.The illumination <strong>of</strong> the <strong>bridge</strong> willbe an important part <strong>of</strong> its aesthetics.For the main tower, a total <strong>of</strong>16 fixtures will be mounted on theexterior <strong>of</strong> the parapets, and an additionaleight will be located at thetower bases. The 24 fixtures will illuminatethe outside faces <strong>of</strong> the maintowers.The lighting <strong>of</strong> the span dependson whether the <strong>bridge</strong> will be constructed<strong>of</strong> concrete or steel. Reflectivematerial, rather than lightingfixtures, will be used on deck wallsurfaces if concrete is used. If the<strong>bridge</strong> is constructed <strong>of</strong> steel, it willbe lit by a glowing surface mountedon diffused frosted glass industrialfixtures.Sixteen fixtures on the outside <strong>of</strong>the parapets, along with eight at thepylon bases, will be used to illuminatethe outside <strong>of</strong> the pylon faces,and 11 metal halide lamps will lighteach <strong>of</strong> the six cable blocks. Forsecurity, 16 metal halide pier lightingfixtures will be used below the<strong>bridge</strong> deck to illuminate the lowerportion <strong>of</strong> the piers and bases.It’s all stagedThe new Q-Bridge will be builtin three stages. The first half <strong>of</strong> the<strong>bridge</strong> will be constructed alongsideand to the north <strong>of</strong> the exist-ASPHALTThe Sustainable PavementENERGY & RECYCLING PERFORMANCE WATER QUALITY CLEAN AIR & COOL CITIESAsphalt is the sustainable materialfor constructing pavements.Learn more at PaveGreen.com.From the production <strong>of</strong> the paving material,to the placement <strong>of</strong> the pavement on theroad, to rehabilitation, through recycling,asphalt pavements minimize impact on theenvironment. Low consumption <strong>of</strong> energyfor production and construction, low emission<strong>of</strong> greenhouse gases, and conservation<strong>of</strong> natural resources help make asphalt theenvironmental pavement <strong>of</strong> choice.• What industry is America’s number <strong>one</strong>recycler?• How can asphalt pavements reduce roadnoise?• What <strong>kind</strong>s <strong>of</strong> asphalt pavements can helpmanage stormwater?• How can asphalt pavements mitigate theurban heat island (UHI) effect?Visit PaveGreen.com to learn more.Circle 753ROADS & BRIDGES • JUNE 2008 •27