Alvord Lake Bridge

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Alvord Lake Bridge
HAER-Alvord Lake.jpg
A view of the Alvord Lake Bridge looking toward the east
Coordinates37°46′08″N 122°27′18″W / 37.7690°N 122.4549°W / 37.7690; -122.4549Coordinates: 37°46′08″N 122°27′18″W / 37.7690°N 122.4549°W / 37.7690; -122.4549
CrossesPedestrian entrance to San Francisco's Golden Gate park
LocaleSan Francisco
Official nameAlvord Lake Bridge
Heritage statusAmerican Society of Civil Engineers civil engineering landmark
Characteristics
MaterialReinforced concrete
Width64ft
Longest span20ft
No. of spans1
History
DesignerErnest L. Ransome
Opened1889

The Alvord Lake Bridge was the first reinforced concrete bridge built in America. It was built in 1889 by Ernest L. Ransome, an innovator in reinforced concrete design, mixing equipment, and construction systems. The bridge was constructed as a single arch 64 feet (20 m) wide with a 20-foot (6.1 m) span .[1] Ransome is believed to have used his patented cold-twisted square steel bar for reinforcement, placed longitudinally in the arch and curved in the same arc. The face of the bridge was scored and hammered to resemble sandstone, the interior features calthemite [2] "stalactites" (concrete derived secondary deposits) which have subsequently grown in later years after the initial construction.

E. L. Ransome left San Francisco a few years later, frustrated and bitter at the building community's indifference to concrete construction. Ironically, the city's few reinforced concrete structures, including the Alvord Lake Bridge, survived the 1906 earthquake and fire in remarkable shape, vindicating Ransome's faith in the method. The bridge was designated a civil engineering landmark by the American Society of Civil Engineers in 1969.

The Alvord Lake Bridge, which arches over a pedestrian walkway near the lake in San Francisco's Golden Gate Park, allows visitors coming from the Haight Ashbury District and entering the park from the east at Stanyan Street to access the rest of the park safely and directly by providing a grade-separated crossing underneath busy Kezar Drive.

References[edit]

  1. ^ Jackson, Donald (1996), Great American bridges and dams, New York: Wiley, ISBN 978-0-471-14385-7
  2. ^ Smith, G.K. (2016). "Calcite straw stalactites growing from concrete structures", Cave and Karst Science 43(1), 4-10. http://bcra.org.uk/pub/candks/index.html?j=127