SCHEMATIC DESIGN FOR A NEW BAY BRIDGE

A Bridge For The 21st Century

Prepared by Christopher Alexander and Randall Schmidt for the Honorable Jerry Brown, Mayor of Oakland at the request of the City of Oakland.

CONDITIONS: PARAMETERS GIVEN TO US AS THE BASIS FOR THE DESIGN:

A Beautiful And Visionary Bridge

Cost must come in under present Caltrans proposals

Trains must be included

Pedestrians and bikes provided with a beautiful place

Ultra--modern and technically advanced

Maximize views from the bridge

Beautiful at night, with lighting

Satisfy San Francisco requirements at Yerba Buena Island.

Alignment to satisfy City of Oakland requirements at the Oakland anchorage and Gateway Park.

It was emphasized to us that to be competitive with the Caltrans design, cost is the #1 issue, and is the necessary underpinning to get a new bridge design to be accepted as superceding the present Caltrans suspension bridge design

CENTER FOR ENVIRONMENTAL STRUCTURE

ARCHITECTS   ENGINEERS   CONTRACTORS

The work so far commissioned has been done by a team of four architects and engineers. We have carefully studied issues of functionality, preliminary structural design, dynamic behavior, design failure modes, and cost estimates. It must be borne in mind that this is a schematic design, and that all the statements in this report are of a highly preliminary nature.

CONTENTS

COMPARATIVE COST

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COST ANALYSIS

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VISIONARY DESIGN

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STRUCTURE

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DYNAMIC BEHAVIOR

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CONSTRUCTION  TECHNIQUE

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TRANSPORTATION

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THE DRIVER

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THE PEDESTRIAN

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THREE GREAT BAY BRIDGES

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ALIGNMENT

COMPARATIVE COSTS

SUMMARY

Present Caltrans Suspension Design

$1.50 billion to $1.65 billion

Trains not included but weight provision of 1400 lbs/lf has been made; removal of shoulder is required

Bikes included at higher figure, but bikes and pedestrians are along the edge of the freeway lanes.

Aesthetic lights can be included at extra cost of $15--18 million.

CES Design $1.44 billion

Design includes high speed passenger rail, and rail connection to west bridge span, without removing lanes.

Beautiful lighting is included in the cost.

Bikes and pedestrians are included at no extra cost

An innovative inspiring vision for the 21st century

DETAILED COST ANALYSIS

All figures in millions of $

CALTRANS
SUSPENSION
CES BRACED
PLATE GIRDER
FOUNDATION 255 305
SUPERSTRUCTURE 350 280
EXTRAS FOR BIKES, LIGHTS, ETC. 150
ANCILLARIES 24 28
35% MOBILIZATION +
CONTINGENCIES
224 215
OTHER 644 613

TOTAL COST 1647 1441

Note: 徹THER includes Oakland plaza, demolition, road construction, escalation to 2002, roadway construction, supports, ground motion, life cycle cost, and post--earthquake repair cost.

A VISIONARY DESIGN FOR THE 21ST CENTURY

The bridge is a sequence of linked soaring curved diamondlike structures, strung like a chain of jewels  on a necklace.

The CES bridge, unlike current proposals, centers around the beauty experienced by the driver crossing the bridge.

The design draws both its beauty and its cost saving, from the efficient action of the pierced plate girders. The light colored concrete plates, glistening in the light of the bay, pierced with beautiful openings, and working together with X--braces, tension cables, and stiffening ribs, create a new bridge technology.

In the tradition of Maillart, Nervi, and Calatrava, concrete and steel are used together, in an efficient combination.

Concrete is used in an efficient deep thin plate girder structure to create strength, stiffness, and shapes of great beauty, which are efficient in cost because of their light weight, and reduction of material.

Steel is used in its most efficient tension cable mode to create a light airy structure, of low cost.

In this bridge, ornament and efficient structure are combined, to produce something technically exciting, highly efficient, yet ultimately appealing to the most romantic elements in people of the Bay Area who will see this bridge every day of their lives. The bridge is part of the identity people feel, and it must be able to play that role, and to etch itself into peoples mental and emotional life.

STRUCTURE

An Innovative State--of--the--Art Structure Which Makes Maximum Use Of Modern Concrete Technology

DYNAMIC BEHAVIOR

An Innovative Structure specifically designed to damp oscillations during dynamic loading in a major earthquake

>From a structural point of view, perhaps the greatest matter, and one which necessarily attracts most attention, is the expected behavior of the structure in a massive earthquake, particularly the out-of-plane behavior.

The classic suspension bridge is highly flexible, and therefore tends to perform well, providing footing design is good: the structure vibrates relatively freely, the motion is gradually damped, and the structure returns to its original state.

More rigid or non-cable based structures tend to behave differently. The structure, being rigid, tries to resist the lateral loading within its strength limitations. But once the strength limit is reached, the structure may fail. One structural technique developed to avoid this is to build in sacrificial components, weak links designed to yield or permanently bend first before any other part of the structure. These components flex back and forth dissipating energy, damping the motion, and preventing failure of other more vital components of the structure. These damaged components are designed to be relatively cheaply removed and replaced.

The CES bridge design is based on this approach. Each of the diamond shaped cantilever sections along the bridge's length will vibrate individually. Due to their differing sizes, they have different fundamental periods, and thus the oscillations will be out of phase from bridge segment to segment. But the small connecting links between the cantilever sections contain sacrificial components which allow the neighboring cantilever sections to move independently,while the the sacrificial links experience a controlled failure, absorbing energy and damping the bridge's motion, leaving the bridge entirely intact, with a repairable amount of controlled damage at each link. After a major earthquake, these sacrificial components can be easily replaced, and the bridge quickly restored to active service.

CONSTRUCTION TECHNIQUE

Erection Sequence

In general, plate elements will be pre--cast, floated on barges, then lifted into place.

As elements are lifted into place, they are tied together, and given tension behavior, by post--tensioning steel cables which lie in ducts within the concrete shell members.

Each double cantilever (diamond) has a balanced design, which allows incremental addition of pieces, two at a time.

On occasion, some plate elements might be made by tilt--up techniques, using the road bed itself as a casting slab.

Footnote: The braced and stiffened plate girder design might also be realized in steel, instead of concrete. Using advanced braced plate design, and hollow box sections. We are currently exploring this option.

TRANSPORTATION

the bridge provides a full--spectrum mix of cars, trucks, buses, carpool lanes, trains, bikes, pedestrians and ferries

THE DRIVER

This Bridge, Unlike Current Proposals, Centers Around The Experience Of Driving

The space of the lower deck is high (18 meters, or about 5 stories) and filled with light.

Because the bridge is narrow, drivers see the views from both sides, and the views are framed in the open arches of the side wall.

Beautiful daylight coming in from the sides.

Breezy to make driving a beautiful experience

Arches along the sides

High and graceful

Big arches to drive through

Lights in all openings

Beautiful lighting at night, illuminating the bridge, and given by the shape of the bridge structure without extra cost

Driving along the upper deck, the driver is passing through the spaces created by the superstructure of the plate girders.

View to water, sky, Oakland and San Francisco, framed by the openings in the girder.

Our models of the lower deck show a beautiful arched structure, twice as high as the present lower deck, with light, breeze, and beautiful views.

PEDESTRIANS BIKES

BOATS

An Asset to the Bay Area

THREE GREAT BAY BRIDGES

The new design has a very strong relationship to the two great Bay Area bridges, the Golden Gate Bridge and the West span Bay Bridge. As can be seen in the photograph of all three bridges together, the three form a family together.

The new bridge respects the two older great bridges, and the cluster of three bridges adds significantly to the value and importance of the Bay.

CROSSOVER ALIGNMENT

We have not had time or sufficient information to fully assess the alignment problem. However we make the following preliminary observations:

CURRENT STATUS

Design work is still going forward for the Caltrans design for the Bay Bridge. Lots of people think it is ugly, impractical and not at all what the cities need. Here is our proposed design which meets budget requirements, is technically innovative, and beautiful. We post it for your enjoyment. As far as we know, the one people don't seem to like is going to be built instead.