Print this page Bridging San Francisco Bay
J.M. Syken
Course Outline
In this course, we will examine the background and events leading up to the design, construction and completion of the San Francisco-Oakland Bay Bridge in San Francisco, California. To fully understand and appreciate the bridge, we’ll examine the social, economic, political, technical etc. events/requirements that would ultimately create the great edifice.
Furthermore, we will examine in-depth and detail the engineering and architecture involved in designing the bridge, in particular the sub-aqueous structures, superstructure/s and the aerial spinning of the wire cables for the double suspension-spans. Also, we’ll focus on the construction methods, materials and systems utilized. We will examine the many retrofits/alterations made to the bridge since its opening in late 1936. As well, we will examine the effects of the October 1989 Loma Prieta earthquake on the bridge, seismic retrofits in its wake and the complete replacement of the east bay crossing resulting from that event.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
At the conclusion of this course, the student will:
- Understand/appreciate the origins of the bridge dating back to the 1860s and the early attempts to build a trans-bay bridge;
- Understand/appreciate how San Francisco was isolated from the mainland to the east and why a bridge was needed to end that isolation forever;
- Understand/appreciate how the advent of the “auto age” by the 1920s made bridges and roads mandatory, not optional;
- Understand/appreciate the role played by the State of California in promoting and building the Bay Bridge through various existing state agencies and the creation of new state agencies specific to the bay Bridge;
- Understand/appreciate why the War Department was the main opponent to a trans-bay bridge and how the election of Herbert Hoover as POTUS in 1928 ended that opposition and made federal financing/approval possible;
- Understand/appreciate the “team effort” involved in designing the Bay Bridge and the roles played by C.H. Purcell, his capable staff of state engineers and the Board of Consulting Engineers;
- Understand/appreciate the difficulties encountered in establishing appropriate bridge alignment/s, span types, pier types etc. based on the geology of the bay;
- Understand/appreciate the difficulties encountered and overcome in sinking pneumatic caissons to great depths;
- Understand/appreciate the mix of bridge types used and how Yerba Buena Island was used as a “stepping stone” across the bay; and
- Understand/appreciate the many changes, alterations, retrofits, replacements etc. made to the bridge, mainly from 1959 to 1963 and post-1989 (after the Loma Prieta earthquake).
Intended Audience
This course is intended for architects, engineers, contractors and other design/construction professionals.
Benefit to Attendees
The attendee/s will gain an intimate knowledge and insight into the creation of one of the world’s greatest engineering achievements: The San Francisco-Oakland Bay Bridge.
Course Introduction
Like New York City; before the Hudson River was spanned by the mighty George Washington Bridge (1931), San Francisco found itself isolated from the rest of the country by a wide body of water. The task was easier in NYC since the Hudson was about a mile wide in upper Manhattan and bridge engineering had advanced significantly enough by the 1920s to make a single suspension-span feasible. However, San Francisco was separated from the East Bay by about four miles of deep water thus a single “grand leap” was just not possible. But there was one advantage San Francisco had that could make a bridge possible; a lump of rock about halfway distant from the Oakland shore called Yerba Buena Island. Ironically, geological studies of the bay floor indicated a rock ledge following the preferred alignment from Rincon Hill in San Francisco to Yerba Buena. It was deep, but not impossible to reach using foundation expert Daniel Moran’s “Floating Cylinders” deep-water caisson design. To span the two miles between San Francisco and Yerba Buena, several bridge designs were considered including a conventional suspension-span with a 4,100-foot main-span. A double (in tandem) suspension bridge with a central anchorage was chosen instead, the first of its kind ever built. The island could/would be traversed via viaducts and a large bore tunnel. The east bay could not support heavy spans since piers could not be founded on rock, it was just too deep to get to. The compromise was a large cantilever and through/deck trusses supported by piers founded on hard clay to get to the eastern shore. It may not have been pretty, but it worked and for the residents of the East Bay, the Bay Bridge’s beauty rests purely in its functionality.
Course Content
In this course, you are required to view/study the following slideshow and the materials contained in the web pages:
Bridging San Francisco Bay (printable handout in PDF, 10 MB, see Note A below for downloading instruction)
Bridging San Francisco Bay (non-printable slideshow for screen-viewing only, 47 MB, see Note A below for downloading instruction)
Bridging San Francisco Bay (Video)
The New Bay Bridge: Earthquake Makeover - KQED QUEST (Video)
https://www.youtube.com/watch?v=xLKbRTVYUk8&t=2s (Film: New Bay Bridge - 41:47)
Note A: Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right-clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader from your computer.
Course Summary
On November 12th 2011, the Bay Bridge celebrated seventy-five years of service to the Bay Area. After the collapse of an upper deck section of the east bay crossing during the Loma Prieta earthquake in October 1989, the Bay Area found out just how important the Bay Bridge is to the lifeblood of the region. With the bridge closed, the thousands of commuters and commercial vehicles that use the bridge daily found out what life would be like without a Bay Bridge. The earthquake would be a call to action and the realization that the stiff cantilever and through and deck trusses of the east bay crossing were just too rigid to be able to withstand the next “big one” – an earthquake even larger than the Loma Prieta quake expected at any time. The race was on to build an entirely new east bay crossing capable of “riding out” the next big earthquake. The west bay double suspension-spans faired better during Loma Prieta since suspension bridges are inherently more flexible than rigid structures such as a cantilever. Even so, steps are being taken to ensure that there will always be a Bay Bridge serving the people and commerce of Northern California of which the Bay Bridge is - and always will be, an integral part.
Related Links
For additional technical information related to this subject, please visit the following websites:
San Francisco Oakland Bay Bridge
https://www.youtube.com/watch?v=FuWM6-xOQCY
(Film: The world's Longest Bridges - 08:50)
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
