ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/335723
CONCRETE BRIDGE PRESERVATION 1st Street Bridge over Los Angeles River Preserving a historical monument by Romeo Firme and Gary Buelow, Atkins The 1st Street Bridge, inspired by the civic architecture of Paris and Rome, spans over the Los Angeles River near downtown Los Angeles. After more than 80 years of use, the historic bridge needed to be widened and improved to accommodate the ever-increasing transportation demands of a mega-city. In its ultimate confguration, the bridge has capacity for two new tracks of the Metro gold line and 18,000 motorists a day. A unique set of challenges was posed by the modifcation of the existing bridge to accommodate a double track light rail transit corridor and meet current design standards; construct the widened portion; and re-use the triumphal arches while maintaining traffc on the bridge, local roads, and 15 sets of live railroad tracks. A Historic-Cultural Monument In keeping with the neo-classical architecture, the widened north side of the bridge was built with the same aesthetics as the original bridge. The bridge portion over the Los Angeles River consists of two identical deck arch spans on a central pier with pylons at each end. The graceful open spandrel arch has vertically curved concrete arch ribs with equally spaced vertical columns supporting foor beams and a deck slab. The girders have cathedral arches and the exterior girders have ribbed overhangs. The spandrel columns, which are part of the arches above the river, are arched in shape and highly decorative. At the ends of the arches and at three other locations, massive 200,000-lb masonry blocks in the shape of Roman triumphal arches rise above the river piers. Behind the piers are projecting balconies with benches. The plain frieze is fnished with an architrave cornice. The structure is heightened above this entablature with a wide panel bearing plain incised rectangles, fnally surmounted by stepped rows of narrow horizontal blocks. The neo-classical detail extends to the entablature pattern on the fascia girders and to the bracketing for the sidewalk. The railings are simple arcades replicating the historic railing at the south side of the bridge. Bridge lights are replicas of the original lantern electroliers, serving to recreate the look of the bridge when it was frst opened in 1929 during the City-Beautiful era in Los Angeles. Modifications to the Existing Structure The existing structure was modifed to accommodate two lanes of vehicular traffc in each direction, two pedestrian sidewalks, and two new railroad tracks. Of these loads, the biggest challenge was to accommodate two sets of train tracks, as these were much heavier than the truck loads in the original design. To mitigate the additional weight, the (continued next page)