Engineering Ethics

Chapter 7

1989: San Francisco–Oakland

Bay Bridge Earthquake

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THE REPORTED STORY

The New York Times Abstract:

A devastating earthquake rocked the San Francisco Bay area at rush hour

last night, killing at least 200 people, collapsing a mile-long span of an Interstate

highway and wrecking part the Bay Bridge to Oakland. (Barron, 1989)

THE BACK STORY

TRANSPORTATION IN THE BAY AREA IN THE 1920S

During the 1920s, the San Francisco Bay area was the most densely settled

region of California. As San Francisco and Oakland grew during this time,

transportation between these two major cities became more important.

Passenger and vehicular ferries carried citizens between both ports across the

San Francisco Bay. In 1929, passenger ferries carried 36 million passengers

and vehicular ferries carried 10 million passengers with their automobiles.

During these years, the number of annual passengers was decreasing while

the number of annual autos was increasing. This was not surprising, because

Californians owned one car for every 2.7 people in 1929. East Bay residents

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used the East Bay Highway to travel from suburbs to the Oakland area.

Vehicles were ferried from Berkeley to Hyde Pier in San Francisco. Once in

San Francisco, vehicles used the Bay Shore Highway to travel between San

Francisco and San Mateo.

The Southern Pacific railroad also had indirect routes between the two

cities. One railroad crossing across the bay spanned Dumbarton Port in

Alameda County and Redwood City in San Mateo County; the second

crossing spanned Benicia and Martinez.

With this transportation system in place, the San Francisco–Oakland Bay

bridge began its construction in 1933. Designed only to improve highway

and mass transit services between the East Bay and San Francisco, this

bridge was congested on the day of its dedication in 1936 and has remained

congested almost without interruption (HAER, 1999).

BRIDGE DESIGN AND CONSTRUCTION

The Bay Bridge design was based on the following requirements:

• Capacity of six lanes for highway traffic and at least two operative

and one passing or emergency track for interurban trains;

• One or two bridge spans between San Francisco and Yerba Buena

island (the west channel), and one span between the island and

Oakland;

• Vertical and horizontal clearances of 220 feet and 1650 feet,

respectively, mandated by the War Department.

Unlike other prominent bridges built at the time, such as the Golden Gate

Bridge, the Bay Bridge was designed by committee, rather than under the

vision of one designer/architect. It was efficiently designed during a 24-month

period, from early 1931 to early 1933. In 1931 the California legislature

authorized the California Toll Bridge Authority (CTBA), which it had

created in 1929, to build the bridge and provided $650,000 for its design.

C. H. Purcell, who studied civil engineering at Stanford University, was

appointed chief engineer for the bridge; Charles Andrew, who studied civil

engineering at the University of Illinois, was named as his assistant, or bridge

engineer.When Purcell and Andrew’s requested exemption from civil service

was approved, they hired a talented team of more than 50 engineers along

with allied specialists, including surveyors, draftsmen, and a clerical staff. Two

prominent team members were Ralph Modjeski, one of the best known

bridge engineers of the early 20th century, and Daniel Moran, one of the best

known foundation engineers.

Due to the horizontal clearances requested by the War Department, a

suspension design, rather than a cantilever design, was selected for the

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