California Bridges
The San Francisco Bay is home to some of the most famous and magnificent
bridges ever built, including the Golden Gate Bridge, San Francisco-Oakland
Bay Bridge, Richmond-San Rafael Bridge, Hayward-San Mateo Bridge and the
Dumbarton Bridge. Collectively, these five bridges represent a gamut of
engineering structures and designs. It's no wonder, given the diverse geography
they must span.
To the west of San Francisco sits the Pacific Ocean and due east through
the strait of the Golden Gate lies the San Francisco Bay, extending 10
miles northeast to the San Pablo Bay entrance and 40 miles southeast into
Palo Alto. At its greatest width the bay measures 13 miles with depths
reaching over 200 feet, just inside the Golden Gate; yet, 70 percent of
the bay is less than 12 feet deep. At points along the 50-mile length of
the bay, five structures of engineering excellence, some considered impossible
to build, span gracefully over 23 miles of the bay waters and allow travelers
to visit San Francisco, the peninsula and the East Bay easily, quickly
and safely.
Historic Landmark NO. 974 GOLDEN GATE
BRIDGE - Construction of the bridge started in 1933. Engineer Joseph
Strauss and architect Irving Morrow created an extraordinarily beautiful
bridge in an extraordinarily beautiful setting. The designs for the
Golden Gate Bridge showed the greatest attention to artistic detail,
especially on the two streamlined moderne towers. The bridge's 4,200
feet of clear span (from tower to tower) was the longest in the world
until 1959. On April 19, 1937, the bridge was completed and the official
dedication took place on May 27.
Location: Observation area, N end of bridge
USGS Quadrangle Sheet Name: SAN FRANCISCO NORTH
Designed with a number of factors in mind, each bridge has its own navigational
clearance, foundation conditions, total length of structure, cost and aesthetics,
according to the California Department of Transportation, or Caltrans.
Crossing the strait of the Golden Gate from San Francisco to the Marin
headlands for 1.7 miles is the world-renowned Golden Gate Bridge, easily
identified by its International Orange color. Opened in 1937, the bridge
was built at a cost of $33 million and 10 workers' lives. The single-suspension
span is anchored off the shores of the bay by twin towers that reach skyward
750 feet, and was once taller than any building in San Francisco. To support
the suspended roadway, two cables more than 7,000 feet in length, containing
70,000 miles of wire stretch over the top of the towers and are rooted
in concrete piers on shore. Ten years in planning due to formidable opposition,
but only four years in actual construction, the Golden Gate Bridge brought
the communities of San Francisco and Marin county closer together.
The Golden Gate's eastern cousin, the San Francisco-Oakland Bay Bridge,
holds the title of longest high-level bridge in the world at 8.4 miles.
Completed in 1936, the Bay Bridge earned the honor of being declared the
seventh wonder of the world in 1955 by the American Society of Civil Engineers.
It is actually two different types of bridges--suspension on the San Francisco
side and cantilever on the Oakland side--connected via tunnel through Yerba
Buena Island. Due to the extraordinary depth of the water, ranging from
50 to 105 feet, and a bay floor thick with several layers of mud, the building
of the bridge brought about new engineering challenges. Special caissons,
watertight chambers, were designed for digging through the Bay floor in
order to embed the bridge's foundation in bedrock. As more people began
making the East Bay their home, the Bay Bridge became the most heavily
traveled bridge in the Bay Area, third busiest in the country, carrying
more than 250,000 vehicles daily.
At the north end of the bay is the cantilever-truss Richmond-San Rafael
Bridge which stretches 5.5 miles. This bridge has the dubious distinction
of being struck on several occasions by passing ships, including a World
War II vessel and a Navy radar ship that struck the bridge twice as the
ship spun around. However, the bridge suffered no serious damage. Less
elegant than its sister bridges, upon completion it was dubbed by bay area
residents the "roller coaster bridge." But, even in its austerity, the
bridge glides effortlessly across the bay, linking travelers to the hills
of Marin and the wine-growing regions of Sonoma and Napa Valley.
Towards the south of the bay lies the San Mateo-Hayward Bridge, "6.8
miles of silver ribbon stretching gracefully in stunning relief across
the bay," boasts Caltrans. The second to the youngest in the family of
San Francisco Bay bridges, the bridge designers gave high priority to its
aesthetics. Constructed of steel girders and trestles, the San Mateo-Hayward
Bridge achieves its slim silhouette through the innovative technique of
placing all bracings and hinge details on the inside of the box girders,
making the structure the world's longest, untraced girder span. As a result,
the bridge earned the American Society of Engineers' "Outstanding Civil
Engineering Achievement" honor and the American Institute of Steel Construction's
"Most Beautiful Bridge- Long Span" award in 1967. Opened for use October
31, 1967, the San Mateo-Hayward Bridge provides closer proximity to the
San Francisco International Airport for people in the south and east bay
communities.
In 1927 a private corporation built the first of the bay bridges, the
Dumbarton which crossed the narrowest portion at the south of the bay,
a short 1.2 miles. The state purchased the bridge in 1951 and after several
studies concluded that a replacement structure was needed. In 1984 the
state completed construction on the new bridge, made of steel box girders
and prestressed concrete spans totaling 8,600 feet. The bridge's graceful
shape is heightened by the 15 twin trapezoidal girders that seem to float
on the concrete piers extending just above the water. The original structure
was completely demolished in 1985. The bridge welcomes pedestrians and
bicyclists on a separate path separated by a concrete safety barrier. Partially
located within the San Francisco Bay National Wildlife Refuge, the toll
plaza canopy serves as an overpass for visitors to the Wildlife Refuge
and the Coyote Hills Park.The Dumbarton Bridge connects the counties of
San Mateo and Alameda and helps to lessen the congestion for commuters
traversing to the East Bay and the lower San Francisco peninsula.
The five bridges of the San Francisco Bay provide not only an expedient
means to residents' daily commute, but also offer exceptional combinations
of grace and strength that commuters and visitors alike can appreciate
as they traverse the Bay Area.
