Alvord Lake Bridge

Alvord Lake Bridge
A view of the Alvord Lake Bridge looking toward the east
Coordinates	37.7690°N 122.4549°W / 37.7690; -122.4549
Crosses	Pedestrian entrance to San Francisco's Golden Gate park
Locale	San Francisco
Official name	Alvord Lake Bridge
Heritage status	American Society of Civil Engineers civil engineering landmark
Characteristics
Material	Reinforced concrete
Width	64ft
Longest span	20ft
No. of spans	1
History
Designer	Ernest L. Ransome
Opened	1889
Location

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 . 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 "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 Alvord Lake Bridge, which arches over a pedestrian entrance to San Francisco's Golden Gate park, was designated a civil engineering landmark by the American Society of Civil Engineers in 1969.