Introduction to SFO Bay Bridge Second Crossing

Feasibility Study Introduction

Ronald F. Middlebrook, S.E., Roumen V. Mladjov, S.E.

CURRENT SITUATION – the existing SFO Bay Bridge was completed in 1936.  It was then, and still is, one of the grandest engineering achievements in the Art of Bridge Engineering. The Bay Bridge, and its neighbor, the Golden Gate Bridge (completed at about the same time) represented the culmination of more than 100 years of development of bridge engineering and construction in the United States.  Traffic increased to an average 280,000 vehicles daily in the early 1990’s creating heavy congestion at peak commute hours.  The East Crossing (from Yerba Buena Island (YBI) to Oakland suffered local damage during the ’89 Loma Prieta earthquake.  In the mid-1990’s, Bay Area officials decided the East Crossing should be replaced.  The project was termed a seismic safety replacement of the East Crossing which meant only the earlier existing capacity could be replaced.  Construction started in 2002 and is scheduled for completion in late 2013.  After more than $7 billion spent and 12 years of construction the Bay Bridge will not have a single additional lane to relieve the congestion, already intolerable in the 1990’s.  The relentless increase of Bay Area population only makes congestion worse.

GOAL – the primary goal is to improve vehicle traffic capacity of this major Bay crossing between San Francisco and Oakland.  This proposal would increase that capacity by 80%, from 5 lanes to a total of 9 lanes in each direction.

THE SOLUTION – is to build a second crossing approximately parallel to the existing bridge on the south-east side of the current alignment. The west span should be a new bridge in harmony with the existing suspension bridge; the east span should be the abandoned existing structures retrofitted and relocated on to new foundations near the current alignment.

SAVING THE EXISTING EAST CROSSING OF THE BAY BRIDGE; AN HISTORIC LANDMARK – It is important to save and reuse the original east crossing of the bridge; otherwise to be demolished.  These structures are a symbol of the greatest era of American development, representing the structural types mostly used in building North America’s infrastructure in the 19^th and first part of the 20^th century. There are more than 23,000 historic truss bridges in the U.S.

AEsthetic Considerations -- The exposed steel typical for bridge crossings may not be largely accepted as classic, beautiful architecture, however the steel truss structures of the entire bridge are similar to the structures of several great, iconic bridges such as the Brooklyn and George Washington Bridges in New York, the Quebec Bridge, and the Sidney Harbor Bridge.

The truss type steel framing is beautiful; its forms are purely functional following the structural demand.  It reminds one of the famous Eiffel Tower, a structure much criticized at the time of its construction, but later acclaimed as one of the World’s top engineering and architectural achievements, becoming the symbol of Paris and of France.

STRENGTHENING AND REFURBISHING THE EXISTING EAST SPAN -- The best saving of an historic bridge is as a reuse or replacement bridge.  Often the strengthening consists of reinforcing all elements that are found not adequate for current code demands.  Occasionally, a more effective approach involves adding members to create continuity between structural elements.  For reuse of the original East crossing structures for the proposed Second crossing, the most efficient approach may be a combination of both, that is creating continuity between the ends of existing trusses and strengthening or replacement of individual elements found to be deficient.

Both types of truss spans, through truss and deck truss, can be easily transformed to continuous truss systems using four to five bays by adding new verticals and top chord elements at the supports.  This will automatically reduce the strength demand at the bays representing about 75 – 80% of the span lengths.

The cantilever truss structure can be strengthened by using post-tensioning to impose reversed tension/compression axial forces in the main bridge elements. A cable-stayed system seems an appropriate option for such modification.  This approach can relieve the dead load stresses in the existing structure by up to 75%.

A third way to “buy back” capacity is to reduce dead load.  These existing structures have 6” or 6 ½” reinforced concrete slabs as deck elements.  Removing these slabs and replacing them with a lighter deck system such as a steel orthotropic deck system can provide considerable new excess capacity for the existing systems.

MINIMUM GOAL – to receive meaningful, extended endorsement from the engineering and architectural professional organizations, the historic preservation societies and the media.

MAXIMUM GOAL – to gain strong public sympathy for the idea of building a new 2^nd Crossing using the “retired” structures of the old East crossing and getting those feelings to the decision makers, the Governor and other State of California authorities, through such entities as ASCE, AISC, NSBA, SEAONC, AIA and the California Historic Society.

CHALLENGING PROJECT – accomplishing the idea for a Second Bay Bridge crossing is a very challenging task, but by far not equal to the problems our predecessors had to overcome some 80 years ago, designing and building simultaneously the Bay Bridge and the Golden Gate Bridge during the Great Depression. This project is completely within the capability of American engineers and builders; the only challenge is to persuade the Federal and State transportation authorities to start working immediately on the planning and design for the project.

PROGRAM for DEVELOPING and PROMOTING the IDEA -- All options to promote the idea should be used – articles, project web-site, presentations on professional conferences, publication materials in the media, including professional magazines, newspapers, TV information and interviews, public press-conferences, meetings and discussions with California transportation authorities, letters to the Governor of California and to the appropriate state government authorities.