ASPIRE Spring 11 - Aspire - The Concrete Bridge Magazine

The Harbor Drive Pedestrian Bridgeby Joe Tognoli and Dan Fitzwilliam,T. Y. Lin InternationalAn Iconic Bridge forOne of America’sFinest CitiesFor an engineer, a pedestrian bridgeis like a child’s blank canvas, allowingnearly unlimited creativity in structuralform. There simply are not therestrictions with geometry, structuralsystems, and details that constrain theengineer on a conventional vehicularbridge design. Winding ramps andstairs, inclined members, challengingcable geometry; are all possible on apedestrian bridge.With far more freedom than with avehicular bridge, the pedestrian bridgeallows for greater expression. There areless geometric constraints. Cars justdon’t like highly curved superstructures,but people do. In addition, the practicalmonetary constraints on a vehicularbridge can be greatly reduced on apedestrian bridge. Their smaller scalemakes them inherently less costly, eventhough their unit cost is much higher.Therefore, a community may be ableto spend several million dollars morefor a unique pedestrian bridge, whilethis same amount spent on a vehicularThe bridge carries pedestrians over a series of railroad lines including heavy freight,passenger rail, and trolley lines. It also allows pedestrians to cross over a busy downtownstreet and connects directly with a multi-level parking structure. Photo: Paul Savage. Allother photos and drawings: T.Y. Lin International.bridge would certainly enhance it,but may not be enough to allow foran iconic structure. Fine detail canbe incorporated into the design andappreciated by pedestrians, whereas, ona vehicular bridge, a motorist travelingat highway speed cannot possibly seeor appreciate such detail. With thesefreedoms, and the beautiful SanDiego, Calif., downtown landscape asthe canvas, we were able to create adynamic, dramatic, and iconic structure.The City of San Diego downtownarea is situated on the San Diego Bay.For many years, it has been the goalof the city to complete a pedestrianand bicycle link between the historicBalboa Park and the picturesque SanDiego Bay, dubbed the Park-to-BayLink. The last section of the Link wasblocked by local trolley tracks, severalsets of freight train tracks, and a busydowntown thoroughfare. In 2004,the city commissioned the Centre CityDevelopment Corporation (CCDC),the city’s redevelopment agency, todesign and build a bridge to completethe approximately 2-mile-long Park-to-Bay Link. The site chosen for the finalbridge link is adjacent to the recentlyconstructed Petco Park, home of MajorLeague Baseball’s San Diego Padresand the San Diego Convention Centeron the San Diego Bay, covering over 1million ft 2 .High-Profile SolutionCCDC recognized that the high-profileproject location needed a landmarkstructure to act as the gateway to thecity and as an icon of the revitalizeddowntown area of San Diego. Theyhired the design team to develop aconcept and plans for the bridge andsurrounding plazas. Although manyalternatives were considered for the site,the final bridge type selection was aself-anchored suspension bridge with aninclined pylon.The horizontally-curved superstructureof the 355-ft-long main span is a3-ft-deep, single-cell, hollow, boxgirder section. The full 19-ft 7-in.-section width includes a 9-ft 1-in.-wideprofileharbor drive pedestrian bridge/ san diego, californiaclient: Centre City Development Corporation, San Diego, Calif.bridge design Engineer: T. Y. Lin International, San Diego, Calif.architect: Safdie Rabines Architects, San Diego, Calif.CONCEPT COLLABORATION AND INDEPENDENT CHECK: Strasky and Anatech, San Diego, Calif.prime contractor: Reyes Corporation, National City, Calif.concrete supplier: Hanson, San Diego, Calif.26 | ASPIRE, Spring 2011