historic context of maryland highway bridges built between 1948 ...
historic context of maryland highway bridges built between 1948 ...
historic context of maryland highway bridges built between 1948 ...
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SECTIONFOURPost World War II Technological Developmentsa notable and unusual exception. Post-tensioning was much more common in Europe than NorthAmerica in the material‘s early years (Lin and Kulka 1975:495 – 496).The major impetus behind the push towards increased concrete construction was the Bureau <strong>of</strong>Public Road‘s Criteria for Prestressed Concrete Bridges. This tome, written in 1955, encouragedthe broadened use <strong>of</strong> prestressed, precast concrete bridge member use in the construction <strong>of</strong>interstate <strong>highway</strong> overpasses across the nation (Spero and Berger & Associates 1995: 138).Maryland began to build prestressed concrete <strong>bridges</strong> in 1954. The first example was theShawan Road overpass on the Baltimore-Harrisburg Expressway; it used the post-tensiontechnique. The pretensioned technique was used for the <strong>bridges</strong> on the Princess Anne andFlintstone bypasses. Maryland had 20 prestressed concrete <strong>highway</strong> <strong>bridges</strong> by 1958 (LeViness1958:199; State Roads Commission 1954:63-64).The techniques <strong>of</strong> prestressing and post-tensioning have evolved through the development <strong>of</strong>different high-strength steel and concrete compositions and formwork systems, as well as thecreation <strong>of</strong> methods for compacting concrete via vibration before setting. These developments,and the development <strong>of</strong> prestressing itself, are largely a result <strong>of</strong> the use <strong>of</strong> different materialsrather than design. The prestressed <strong>bridges</strong> <strong>of</strong> the 1950s looked, on the surface, like theirreinforced-concrete companions.Improvements in bridge planning technology, engineering technology, and materials technologyspawned positive reciprocating relationships <strong>between</strong> materials developers and bridge builders.An advance in one field prompted advances in others but the start <strong>of</strong> the trickle-down began withthe introduction <strong>of</strong> the computer. Computer aided engineering initiated engineering efficiency.Engineering advances necessitated the inventiveness <strong>of</strong> steel producers to provide products thatmet new engineering demands. These advances facilitated the construction <strong>of</strong> increasinglylonger, lighter and more economical bridge spans (Burroughs 1975: 463-465, 474).5.3 INDIVIDUAL BRIDGE-TYPE DEVELOPMENTS5.3.1 Metal Truss Bridges (Including Steel)<strong>1948</strong>-1960: 3 Metal truss <strong>bridges</strong> constructed (Maryland State Highway Administration2003).Between 1900 and 1960, the State <strong>of</strong> Maryland standardized metal truss <strong>highway</strong> bridge plans.This bridge type was mainly used for lengthy spans. During the period, the State <strong>of</strong> Marylandutilized Weichert truss systems most especially in west portions <strong>of</strong> the state (Spero and Berger &Associates 1995: 84-85).A notable metal truss <strong>bridges</strong> in the United States during this period include the Nishanic Station,N.J., lenticular truss bridge. This bridge is similar to Roebling‘s Smithfield Street Bridge inPittsburgh, Pennsylvania. Another is the Hanalei, Kauai, Hawaii, dual-truss, combination bridge.Restorationists have recently received awards from the Federal Highway Administration for theirefforts in preserving these <strong>bridges</strong> (Flynn, 2004).During the postwar period, stronger, lighter steel, high-strength bolt technology, crane efficiencyand improved falsework were developed and applied to metal truss bridge building projects.\15-SEP-11\\ 5-3