Master's Project writeup 9-29

REPURPOSING THE PIERS OF THE OLD
SAN FRANCISCO-OAKLAND BAY BRIDGE:
A REPORT DISCUSSING PROJECT FEASIBILITY,
DEVELOPMENT OF ALTERNATIVES, AND DESIGN
Michael Grant Martin
Issue Date: September 30, 2016

Table of Contents
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TABLE OF CONTENTS
Abstract.......................................................................................................................................... 4
Chapter 1: Purpose and Need...................................................................................................... 6
1.1 Background .......................................................................................................................................6
1.2 Purpose...............................................................................................................................................6
1.3 Need....................................................................................................................................................7
Chapter 2: Project Alternatives................................................................................................. 10
2.1 Development of Alternatives..........................................................................................................10
2.2 Alternatives Considered .................................................................................................................11
2.2.1 Alternative 1: No Build Alternative – Leaving the Piers in the Bay..........................................11
2.2.2. Alternative 2: No Build Alternative – Removing the Piers from the Bay ................................11
2.2.3 Alternative 3: Floating Concrete Bridge....................................................................................12
2.2.4. Alternative 4: Constant depth, precast concrete I-girder bridge ...............................................14
2.2.5. Alternative 5: Variable-depth, precast concrete box-girder bridge...........................................17
2.2.6. Alternative 6: Concrete slab-on-piles bridge ............................................................................20
2.3 Comparisons of Alternatives’ Characteristics..............................................................................22
2.3.1. Funding .....................................................................................................................................22
2.3.2. Costs..........................................................................................................................................23
2.3.3. Constructability & Schedule.....................................................................................................24
2.3.4. Public Access............................................................................................................................24
2.3.5. History.......................................................................................................................................25
2.3.6. Climate Change & Sea Level Rise............................................................................................26
2.3.7. Environmental Impact/Advantages...........................................................................................27
2.3.8. Economic Stimulus/Jobs...........................................................................................................28
2.4 Selecting a Preferred Alternative ..................................................................................................28
2.5 Construction Process of the Preferred Alternative......................................................................30
Full Construction Staging of Preferred Alternative ............................................................................30
2.6 Bridge or Barge?.............................................................................................................................34
Chapter 3: Loading Demands.................................................................................................... 35
3.1 Vertical Loads .................................................................................................................................35
3.1.1 Load Paths..................................................................................................................................35
3.1.2. Longitudinal Loading Configurations.......................................................................................36
3.1.3. Transverse Loading Configurations..........................................................................................38
3.2 Lateral Loading Considerations....................................................................................................39
3.2.1. Seismic Loading........................................................................................................................39
3.2.2. Wave Loading...........................................................................................................................40
Chapter 4: Design and Calculations.......................................................................................... 42
4.1 Design...............................................................................................................................................42
4.1.1. Floating Box Design - Longitudinal .........................................................................................42
4.1.2. Floating Box Design – Transverse............................................................................................43
4.1.3. New Pier Caps Design ..............................................................................................................44
4.1.4. ADA Ramp ...............................................................................................................................44
4.2 Hand Calculations...........................................................................................................................46

Table of Contents
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4.2.1. Positive Longitudinal Moment Capacity ..................................................................................46
4.2.2. Negative Longitudinal Moment Capacity.................................................................................47
4.2.3. Transverse Moment Capacity ...................................................................................................48
4.2.3. Longitudinal Shear Capacity.....................................................................................................48
4.2.4. Transverse Shear Capacity........................................................................................................49
4.2.4. Punching Shear Strength...........................................................................................................49
4.2.5. Crack Width and Crack Control................................................................................................51
Chapter 5: Model and Results ................................................................................................... 53
5.1 Model Setup.....................................................................................................................................53
5.1.1 Longitudinal Model....................................................................................................................53
5.1.2. Transverse Model......................................................................................................................53
5.1.3. Verifying Model Validity..........................................................................................................53
5.2 Results of Analysis ..........................................................................................................................56
5.2.1. Longitudinal Model – Structural Analysis Results ...................................................................59
5.2.2. Transverse Model......................................................................................................................59
Chapter 6: Looking forward...................................................................................................... 61
Appendix...................................................................................................................................... 64
A.1 Longitudinal Load Combinations.................................................................................................64
A.2 Transverse Loading Combinations ..............................................................................................72
A.3 Plan Sheets......................................................................................................................................78
A.4 Architectural Renderings..............................................................................................................81
Works cited.................................................................................................................................. 84

Abstract
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ABSTRACT
The San Francisco-Oakland Bay Bridge has been a fixture of the Bay Area since its erection in
1936. In the past, the bridge carried both trucks and trains across the bay, and as needs of the Bay
Area changed, so did the bridge. In 1958, the rail line was removed to make room for increasing
automobile traffic demands. In the 1989 Loma Prieta earthquake, a section of the eastern span
upper deck fell onto the lower deck, resulting in loss of life, and was quickly replaced. As traffic
demands on the bridge continued to increase and fears of the next “big one” loomed, Caltrans
decided that replacement of the eastern span was the proper course of action. Construction began
on the new eastern span in 2002 on a project that would reflect the Bay Area’s past and future, and
its culture ingenuity, and spirit.
Even before the new bridge was open, the State of California began the demolition of the piers that
supported the old eastern span of the Bay Bridge. Beginning in November 2015 with a controlled
implosion on the largest support, E3, in an important shipping channel, the state showed it is
possible to remove these piers from the Bay and have arranged do so for the remaining piers, with
a few exceptions. The piers scheduled to be left behind are piers E19-E23 near the Oakland
approach and pier E2 near Yerba Buena Island. This report will focus on building a pedestrian
walkway bridge between piers E21-E23.
Repurposing these piers instead of removing them has benefits threefold. Firstly, there will be
minimal environmental impact when constructing the pedestrian walkway compared to the
environmental cost of removing them. The San Francisco Bay Conservation and Development
Commission (BCDC) has very stringent regulations on what is built in the bay and how old
structures are removed. Although the removal of pier E-3 went smoothly, reducing the number of
pier that need to be demolished clearly results in a smaller environmental impact.
A major benefit to this project is creating public access to the San Francisco Bay. Plans are already
underway to turn the old Oakland approach into a public park for the surrounding community, and
a pedestrian walkway out over the Bay could act as a venue for numerous activates. Since the
closing of the Berkeley Pier, citizens of the East Bay have been searching for another location to
fish without needed a boat. The walkway could also serve other hobbyists as well, like as a launch
point for kayakers, kite surfers, or windsurfers. The walkway could also be made available for rent
to private parties that need to accommodate large crowds. Most importantly, the park and walkway
could serve as a place for the community to gather and enjoy the beauty of the San Francisco Bay
and the breathtaking architecture of the new eastern span.
As plans to develop the land on the old Bay Bridge Oakland-side approach evolve, it is important
to recognize the piece of history being left behind. The old piers are relics of the Bay Area’s past
and should be honored and preserved. The Bay Bridge opened almost 80 years ago and served
countless passengers in its lifetime. The Bay Bridge was envisioned back in the days of
California’s gold rush but was seen as an impossibility for many years due to the length of the
traverse and the depth of the bay. We should celebrate the incredible triumphs of chief engineer

Abstract
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Ralph Modjeski and his crew should by preserving pieces of the past instead of casually discarding
them.
A final advantage to repurposing the old piers is the financial cost. Based on current costs of
removing the piers in the deeper waters, it would cost a few million dollars to remove each pier in
the shallower water. If piers E19 and E20 are left as bird sanctuaries and piers E21-E23 become
the foundations for the pedestrian walkway, the roughly $15 million could instead be spent on
building the walkway or the nearby park. Rather than spending huge sums to destroy the existing
piers, it would certainly be a better use of funds to create something that people from all around
the Bay Area can enjoy both as leisurely diversion or to soak up a piece of California’s history.
As the old Bay Bridge piers are removed from bay waters, there is a unique opportunity to preserve
history, save money, reduce environmental impact, and most importantly, provide public access
to the Bay. As the Bay area continues to increase its population, it is necessary to create more
public areas for the community to come together. With the closing of the Berkeley Pier, new public
works providing access to the Bay are needed now more than ever. This work proposes the
construction of a new pedestrian walkway out over the San Francisco Bay using the piers that
previously supported the old eastern span of the San Francisco-Oakland Bay Bridge (SFOBB).

Chapter 1: Purpose and Need
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CHAPTER 1: PURPOSE AND NEED
1.1 Background
Since the completion of the new eastern span of the Bay Bridge, the Bay Area Toll Authority
(BATA), in partnership with many environmental resource agencies, particularly the Bay Area
Conservation and Development Commission (BCDC), has been in the process of dismantling the
old eastern span of the SFOBB. The final and most environmentally challenging pieces to remove
are the piers in the water that supported the columns and superstructure. This Masters of Science
project is to determine feasibility and design an unusual bridge structure that reuses these piers. In
an effort to save money, preserve the bay environment and history, and provide maximum public
access to the bay, this project proposes the construction of a pedestrian and bicycle walkway out
onto the two piers nearest the Oakland approach, E21-E23, on the future site of the Gateway Park.
Adjacent to interstate 80, this location will be easily accessible by the public and provide incredible
views of the San Francisco Bay and all she holds.
The bridge piers are about 300 feet apart, so an elevated bridge span would be pushed to its
practical engineering limits. This is one of the most significant challenges facing the design of this
bridge. As the depth of the water changes, so do the sizes of the piers, though E21-E23 are similar
in size and are quite large in order to carry the previous demands of ten traffic lane loads and a
train load, approximately 75 feet by 25 feet—slightly smaller than the piers E19 & E20 which are
about 100 feet by 50 feet. Clearly the axial loads on these piers will never be reached again with a
structure so small in comparison to what they originally carried, however the loads must be applied
carefully as piers are basically a reinforced concrete box with a hollow interior. To ensure that the
piers will not fail in their centers where it is basically a reinforced concrete slab with fixed supports
on all sides, an extra slab will be poured on top of what is already there. This procedure will also
allow for customized connections for the bridge spans, including the necessary shear keys to
prevent motion of the deck. Much of the concrete needed for this pedestrian and bicycle bridge
itself will be cured off-site in a casting yard to avoid wet concrete over bay waters minimize the
environmental impact.
The design should be effective for the functions stated above, but also practical in its construction
and maintenance. The bridge and repurposed piers should pay respect to the historic old bridge
structure while simultaneously complementing the new structure in both style and scale.
1.2 Purpose
The goal of this project is to repurpose some of the old Bay Bridge piers that could be left in the
water after the old span is disassembled. A pedestrian and bicycle bridge will be erected between
the existing piers. This structure itself should be a worthy destination, open to the public, allowing
for increased access to the bay waters along with a safe and comfortable place for the community

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to come together as individuals or as a group for organized events. It should be a resource to the
local community and its visitors, not only a location to view the region, but also a way to
experience the bay. The area could be capable of holding public and private parties, which could
serve as a revenue source for the park and help fund maintenance.
As part of the future Gateway Park, a public bridge with bay access could provide wonderful
education opportunities for the public. It could hold events teaching members of the community
about activities like boating, sailing, and kayaking. The old piers would also be a perfect location
for educating the public about the bay’s history. Plaques and signs could explain the history of the
old Bay Bridge and the transition to the new eastern span. A small science lesson may even spark
the minds of some future structural engineers!
The tertiary objective in constructing a pedestrian/bicycle bridge is to simultaneously provide a
valuable communal resource while minimizing possible environmental impacts to the bay and
costs to the public. BATA has allocated approximately $50 million to remove the piers in the bay,
and if some of the piers can remain, it could be a great financial boon. A portion of the funds that
would be spent on demolition could instead be used to erect a bridge open to the public. This could
potentially save millions of dollars while providing a safe place where the public can gather. Due
to the inherent communal value in opening up access to the bay for the public to use and the
financial cost of removing the piers, building the walkway is arguably more economically
advantageous.
The main purpose of this structure should be to bring the community closer to the bay. The
Gateway Park should make the public feel like a part of the bay, and a pedestrian bridge over the
water will really drive that feeling home. The bridge should bring park patrons right down to the
bay water, if possible, and create a full sensory experience.
1.3 Need
There are many needs for this project with varying degrees of importance. Perhaps the most
fundamental needs that must be provided are those that provide public use and access for the
community. One of the main goals of this project is to create a safe place that is a part of the
community and can provide access to the bay. Per legal requirement, the walkway needs to be
compliant with the Americans with Disabilities Act to ensure that it is accessible to the entire
community. The Americans with Disabilities Act (ADA) of 1990 is a labor law that prohibits
discrimination based on disability. The ADA also requires that all new public projects reasonably
accommodate persons with disabilities. Among the common features to fulfill ADA requirements
is a wheelchair ramp for persons with disabilities with a slope no greater than 1:12. Inclusivity is
an emphasis for this project, and that extends beyond the minimum legal requirements.
In an effort to draw more traffic, the walkway could serve as a point of historical education and
interest. Since the bridge will be immediately adjacent to the new Bay Bridge, it is the perfect

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place to view and admire the architecture and design that the people of the Bay so proudly wanted
displayed in their community. The piers themselves could open up to allow people to walk around
them and view the Bay Bridge and experience all the bay has to offer. The pedestrian bridge and
old piers could also serve as a viewpoint for birdwatching, as there are current considerations to
repurpose the next two piers, E19 & E20, as sanctuaries for birds to lay eggs out of reach of land
predators. Tower viewers/binoculars mounted on the piers would also provide an excellent, close-
up view of the new structure and the bird sanctuaries. These are not only an attraction, could be a
small source of revenue to maintain the park by charging a few cents to get a closer look.
Another way to draw out more of the community is to build a bridge that allows for a range of
activities. With safe, legitimate water access, people could have a launch point for kayaking,
windsurfing, or kitesurfing. These hobbyists would have access to the bay as a whole and could
get closer and more unique views of the beautiful bridge or observe wildlife settling on the bird
sanctuaries. The pedestrian bridge could also cater to other hobbyists like fishermen. Since the
Berkeley pier closed down, the need for a new fishing spot is greater than before. With the
development of the Gateway Park as a whole, this could be a much safer and more secure location
than the Berkeley pier had been in the years before its closure.
Aesthetics are quite important to any structure erected next to something as striking and
monumental as the new eastern span of the Bay Bridge. The pedestrian and bicycle bridge must
follow the same architectural motif as the Bay Bridge without conflicting or competing with it in
any way; the Bay Bridge is the still the main focus. In an effort to follow this vision, the pedestrian
walkway will use the same railings, light fixtures, and concrete color as the Bay Bridge. The
walkway must also stay low to the water so as not to challenge the majesty and size of the Bay
Bridge. Following these guidelines, the pedestrian bridge will only complement the Bay Bridge
rather than steal away any attention. However, in keeping the bridge low and small, other
engineering challenges arise, like how to span such the roughly 300 feet between piers. The
inelegant solution would be to reduce the span length by placing more foundations in the water.
This solution must immediately be discarded, both because the BCDC would likely not allow that
much disruption in the bay for a small project like a pedestrian bridge, and because any new
supports in the water would very likely clash with the elegance of the Bay Bridge. These
architectural and structural needs are very important to the project due to its proximity to a
landmark as gorgeous and important as the Bay Bridge.
One of the main concerns in erecting any piece of infrastructure that must be addressed is the
financial cost. This project, however, has a unique financial situation. The many environmental
and governmental bodies that regulate bay development require that the piers in the bay be
removed in an attempt to revert the bay to its original state. Unfortunately, the cost in removing
these piers is tremendous, costing millions of dollars each. This project should serve as a potential
balance between returning the bay to its original state, providing public access to the bay, and the
financial cost of each respective function. Instead of spending money to remove these piers, some
portion of this money would be better spent providing something new for the community. With
proper project option selection, this could become a financial gain for the community instead of a
cost. Though a lofty goal, one of the needs of this project is to actually save and make money. By

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selecting an inexpensive alternative, this need may not be so improbable. There are also ways for
the pedestrian bridge to generate revenue. The Gateway Park and the new walkway could be rented
out for private functions such as weddings, corporate parties, or small concerts. A temporary,
mobile shelter would be pulled over the walkway in the event of foul weather like rainstorms or a
particularly hot and sunny afternoon. As previously mentioned, tower viewers could provide an
additional continuous, albeit small, source of revenue for the park.
Each new function that this pedestrian bridge serves brings along new loading scenarios. The dead
load of the concrete, railings, lighting, and any other aesthetic features must of course be accounted
for. The most common, everyday loading that the bridge will feel will come from pedestrians
walking out on it. This bridge needs to hold a minimum pedestrian live load of 85 psf at every
location along the bridge and also in the specific locations that create the largest moment and shear
loads. It will be a rare occurrence for the bridge to be fully loaded, but if any events are to be held
over the water, the bridge must be capable of holding large numbers of people. In addition to
pedestrians, the bridge should also be able to carry a single vehicle. Although the bridge will not
carry vehicular loads in general, exceptions should be made for small emergency and maintenance
vehicles. At the very minimum, emergency workers should be able to safely approach the bridge
and easily allow stretchers out over the water for quick access. Another minimum loading
requirement is the need to carry a small maintenance vehicle out on the bridge deck to the piers.
Light fixtures will need repair and fresh paint will need to be applied regularly, and for
maintenance to be efficient, workers will need a vehicle. The bridge must be able to carry the 4-
point load of a single, heavily loaded maintenance truck loaded with work equipment at any
location along the span.
This bridge must also serve the community for a reasonable amount of time in the future. Although
this pedestrian bridge does not fall under AASHTO regulations, it is prudent to use AASHTO as
a guideline. Therefore, this bridge will have a design life of at least 75 years. Structures built on
or over water with long design lives face a new, pressing challenge, climate change. This bridge
must be capable of surviving rising sea levels and the damage associated with it. In order to ensure
that no part of the bridge ever falls below the water surface, more concrete must be added on top
of the piers to increase their height. After the tops of the piers are sufficiently raised, any bridge
fixed to the piers will stay above the sea level for its lifetime.

Chapter 2: Project Alternatives
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CHAPTER 2: PROJECT ALTERNATIVES
2.1 Development of Alternatives
Demolition and removal of the largest pier, E3, took place in November 2015. Investigation of
project alternatives to avoid complete removal of all piers began in March 2016. Various agencies,
stakeholders, and members of the public have a vested interest in turning the old Oakland approach
into a public park. Many alternatives are present in this report, each with advantages and
disadvantages that address various needs of the project. Ideally, the public will have a chance to
voice their opinions on the alternatives and help select one that best fits their needs and desires.
Without public input, the best way to analyze the alternatives was to assign a numerical value to
each alternative’s ability to fulfil the needs of the project. Each considered alternative’s ability to
complete the project needs are outlined in Table 1, shown later. From the results of this table, an
alternative has been selected that best fits the needs of the project and community. Below are a
variety of project alternatives, weighed against each other and one of them is selected as the
preferred alternative.
1. No build alternative—no walkway construction; the piers will need to be removed from the water
per BCDC regulations
2. No build alternative—do nothing; leave the piers in the bay water
3. Floating concrete bridge that connects to the piers
4. Precast concrete I-girder bridge with precast reinforced concrete slab deck lain transversely on
girders
5. Variable-depth, precast concrete box girder
6. Concrete slab-on-piles bridge

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2.2 Alternatives Considered
2.2.1 Alternative 1: No Build Alternative – Leaving the Piers in the Bay
The no build alternative is the option for members of the community who are entirely unconcerned
with development of public land. About twenty years ago, during planning stages for the new
eastern span, the State of California, Caltrans, and the Metropolitan Transportation Commission
committed to removing the piers from the San Francisco Bay after the old bridge was dismantled.
By leaving the piers in the water without repurposing them, the state is reneging on the promise
without putting forth a better option. This alternative fails to achieve almost all of the needs of the
project. The only advantages to this option are that it comes at no additional financial cost to the
community, or with minimal investment, bird sanctuaries could be placed on the piers.
2.2.2. Alternative 2: No Build Alternative – Removing the Piers from the Bay
Much like the previous no build alternative, this option falls short of many of the goals of the
project. It will not provide any increased public access to the bay, which is the primary objective
of this project. Should the rest of the Gateway Park come to exist, it will lack a feature attraction
like the pedestrian bridge. Even the view of the Bay Bridge will seem less impressive from the
shore compared to a vantage point from over the water.

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Alternative 2 does have a few upsides, however. By removing the piers, the State of California
follows through on its promise from twenty years ago and appeases the BCDC’s goal of restoring
the bay to its natural state by removing any foreign objects. The task would also require a
significant amount of labor and specialized workers, creating jobs and injecting capital into the
community. Additionally, once the piers are removed from the bay, the stunning new eastern span
of the SFOBB would stand alone without any other structures distracting viewers or detracting
from its beauty.
2.2.3 Alternative 3: Floating Concrete Bridge
 Proposed Bridge Type
Floating concrete bridges are becoming popular public assets around the world. Alternative 2 is
the least inexpensive bridge alternative outlined here. They can be easily transported via most
waterways and are simple to assemble. Floating concrete bridges can span extremely long distance
due to continuous support from the water beneath them. Spans lengths are mostly limited by forces
acting transversely on the structure, like ocean waves. Floating concrete bridges can rise and fall
with the tidal action but must have a special connection to the land and piers to allow pedestrian
access during in all conditions.
 Bridge Geometry

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The proposed bridge must span the length between each pier, just under 300 feet center-to center.
The walkway will be 30 feet wide which should provide ample space for people to walk around
and to sit down and spend some time over the water. The bridge must be about six feet deep in
order to create sufficient buoyant force to support the self-weight of the bridge and the live load
of any pedestrians and/or vehicles on the bridge.
 Project Seismic Design Criteria
Even though the San Francisco Bay Area is highly seismically active, the unique nature of the
floating concrete bridge gives it a great seismic advantage over traditional bridges. The piers will
feel forces from the bottom of the bay and will shake the bridge, but because it is continuously
supported by water, which cannot sustain or transfer any shear whatsoever, seismic forces on the
bridge itself are entirely eliminated.
 Aesthetic Recommendations
Aesthetic details on the floating concrete bridge will match the new eastern span of the Bay Bridge
as closely as possible. The bridge will use the same white railings were possible and will have the
same light fixtures and will be located on the piers. The concrete in the bridge can also be carefully
colored to match the color scheme of the bicycle path on the Bay Bridge so that pedestrians and
cyclists can look down from the Bay Bridge and appreciate the matching style.
 Purpose & Need
Alternative 3 address the main Purpose of the project by proving public access out over the bay
and repurposing the old bridge piers so they don’t need to be removed. The floating bridge is also
an inexpensive construction option which can actually save money for the community compared
to the millions of dollars associated with removing the piers. Additionally, what money is spend
to construct the bridge would stay in the community. The floating bridge sections can be built in a
local concrete yard and floated out to the construction site. This creates jobs for the concrete
workers in the yard, the tug operators moving the pieces, and of course the construction workers
on the job site.
The floating bridge alternative also does an exceptional job of addressing many of the needs of the
project. Floating concrete bridges and similar structures like floating concrete docks are fixed to
the land and other permanent structures by ramps that can rotate with rising and falling water
levels. The ramp simply needs to be sufficiently long and properly installed to ensure the slope is
ADA compliant in all tidal conditions.
This kind of bridge also offers unparalleled bay access. Since the bridge floats just above the water,
it can serve as an easy launch point for water-sport enthusiast like kayakers or windsurfers. Certain
locations can feature gates or temporary railings to allow quick entry and exit. Even the citizens
that stay on the bridge will be in much closer proximity to the water and may even be able to reach
down and touch it, further strengthening the connection to the bay. The floating concrete bridge
also has the unique aspect of touching the water, which allows pedestrians to actually feel waves

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from the bay beneath them. It may seem minor, but it could be an exceptional experience for many
members of the community. Fishermen will also be able to cast lines from the floating bridge or
the piers, a much needed feature after the closure of the Berkeley Pier.
Another way to connect the park and bridge to the community is to hold events. The floating
concrete bridge is capable of carrying a load of 100 psf, larger than the AASHTO required 85 psf.
This is to allow event planners to have some extra wiggle room in arranging what attractions be
held or what equipment can rest on the bridge. During inclement weather, portable, floating
awnings can be pulled out over the bridge to shelter the event and the guests.
In order to justify the effort put into repurposing the old bay bridge piers, the pedestrian bridge
must serve the community for years to come. The floating concrete bridge has a design life of 75
years; what is typically expected for non-critical, non-building structures. One of the newest
challenges when designing structures that connect to the ocean is the effect of rising sea level due
to climate change. Fortunately, the floating bridge is automatically equipped to handle this
problem. The bridge already rises and falls with the tides and would similarly behave with any
permanent changes in sea level. The piers themselves will need their heights slightly bolstered, but
refinishing the surface is already necessary to give it enough traction over water.
Repurposing the piers also preserves a piece of one of California’s most important historical
structures. The pylons that carried the entire bridge load are mounted on the piers and will remain
in place for this design. Members of the community will have a window into California’s past and
an opportunity to learn about the incredible feat of engineering that helped shape the Bay Area and
the state. Educational stations and plaques will give the public a new appreciation for their home
and its history.
Leaving the four piers allow for not only a pedestrian bridge but also a small bird sanctuary. Piers
E19 and E20, which are further out into the Bay, will remain in place as a location on which birds
can settle. With some small amount of work, environmentalists can shape the piers into a suitable
breeding ground and sanctuary for avian life in the Bay. This could go a long way to offset and
potential harm caused by leaving the piers in the water.
Of course any development in the Bay will have some negative environmental impacts. Moving
the bridge into place will disrupt fish and other wildlife during the process. Pouring the new surface
for the piers also carries potential risk of spillage and dripping. These risks certainly must be
considered, but seem relatively diminutive compared to many other options. Further environmental
studies are necessary to make a fully informed decision.
2.2.4. Alternative 4: Constant depth, precast concrete I-girder bridge

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Precast I-girder bridges are attractive because they are a very common, very well-known design.
Since contractors and concrete workers have so much experience constructing concrete I-girder
bridges, they are relatively inexpensive. The long span length required is a challenge and will
require deep beams in order to carry such a large moment load, but it is certainly achievable.
 Bridge Geometry
and to sit down and spend some time over the water. The bridge must be sufficiently deep in order
to create sustain the large bending moment that such a long span creates.
The highly seismic nature of the San Francisco Bay Area presents a challenge for the concrete I-
girder bridge. In order to avoid exceptionally large beams requiring extra concrete and reinforcing
steel, seismic isolation bearings can be installed on the piers to reduce the earthquake forces in the
bridge. Although these bearings are expensive, the cost is recouped by reducing the material
needed in the superstructure.
Aesthetic details on the concrete I-girder bridge will match the new eastern span of the Bay Bridge
as closely as possible. The bridge will use the same white railings were possible and will have the
same light fixtures and will be located on the piers. The concrete in the bridge can also be carefully

16
colored to match the color scheme of the bicycle path on the Bay Bridge so that pedestrians and
cyclists can look down from the Bay Bridge and appreciate the matching style.
Unfortunately, even with aesthetic considerations, this bridge may still clash with the eastern span
of the SFOBB. Near the pedestrian bridge site, the SFOBB has a varying depth between the
supports. This look does not mesh well with the constant depth of the concrete I-girder bridge and
may cause some complaints. It is important to note, however, that very few people will be able to
compare the two bridges simultaneously; an observer would have to be out in a boat or a kayak
over the water to be able to see the underside of both bridges at the same time. Still, architectural
elements must be considered when erecting a new bridge so close to such an iconic structure.
 Purpose & Need
and repurposing the old bridge piers so they don’t need to be removed. The concrete I-girder bridge
is also an inexpensive construction option which can actually save money for the community
compared to the millions of dollars associated with removing the piers. Additionally, what money
is spend to construct the bridge would stay in the community. The girders and deck can be built in
a local concrete yard and floated out to the construction site on barges. Then the pieces can be
lifted into place using two cranes on another barge. This creates jobs for the concrete workers in
the yard, the tug and barge operators moving the pieces, crane operators assembling the bridge,
and of course the remaining construction workers on the job site.
The concrete I-girder bridge alternative addresses many of the needs of the project. ADA
specifications must be followed absolutely for any public work. Fortunately, the concrete I-girder
bridge will stay at a constant elevation throughout its span from its initial launch point off of the
land. There should be no problems in keeping the pedestrian bridge accessible to all members of
the community.
Since the closure of the Berkeley pier, members of the East Bay have needed another site with bay
access. The concrete I-girder bridge would be a great addition to the community and to the
proposed Gateway Park. The public could walk out over the bay to enjoy the atmosphere and
admire the eastern span of the SFOBB. Fishermen will also be able to cast lines from the floating
bridge or the piers, a much needed feature after the closure of the Berkeley Pier.
Another way to connect the park and bridge to the community is to hold events. The concrete I-
girder bridge is capable of carrying a load of 100 psf, larger than the AASHTO required 85 psf.
held or what equipment can rest on the bridge.
must serve the community for years to come. The concrete I-bridge has a design life of 75 years;
what is typically expected for non-critical, non-building structures. Climate change that results in
rising sea levels poses a problem for structures near the ocean. In order to tackle this problem, the
piers will need an additional layer of concrete atop them to ensure they stay above the king tide

17
not only today, but in the event of sea level rise. Once the tops of the piers are sufficiently tall, the
concrete I-girders can lay atop them and be out of range of the water.
and its history.
2.2.5. Alternative 5: Variable-depth, precast concrete box-girder bridge
Precast box-girder bridges are also very common like I-girder bridges, but they require labor. The
variable depth of the bridge also increases the complexity. Skilled carpenters need to craft the
special formwork for a bridge like this, increasing labor times and cost. The long span length
required is a challenge and will require deep boxes in order to carry such a large moment load, but
it is certainly achievable.

18
 Bridge Geometry
and to sit down and spend some time over the water. The soffit of the bridge is parabolic in shape
over the span length.
The highly seismic nature of the San Francisco Bay Area presents a challenge for the concrete
box-girder bridge. In order to avoid exceptionally large beams requiring extra concrete and
reinforcing steel, seismic isolation bearings can be installed on the piers to reduce the earthquake
forces in the bridge. Although these bearings are expensive, the cost is recouped by reducing the
material needed in the superstructure.
Aesthetic details on the variable depth, concrete box-girder bridge will match the new eastern span
of the Bay Bridge as closely as possible. The bridge will use the same white railings were possible
and will have the same light fixtures and will be located on the piers. The concrete in the bridge
can also be carefully colored to match the color scheme of the bicycle path on the Bay Bridge so
that pedestrians and cyclists can look down from the Bay Bridge and appreciate the matching style.
The concrete box-girder bridge also complements the look of the eastern span SFOBB. Since both
bridge spans would have variable depths, they would each appear to have been designed with the

19
other in mind. Architects of the SFOBB certainly prefer the pedestrian bridge to match their
original vision without distracting from it.
 Purpose & Need
and repurposing the old bridge piers so they don’t need to be removed. The concrete box-girder
bridge design is well-known, but the variable depth requires that skilled carpenters make the forms,
increasing the cost. The box-girders can be built in a local concrete yard and floated out to the
construction site on barges. Then the pieces can be lifted into place using two cranes on another
barge. This creates jobs for the concrete workers in the yard, the tug and barge operators moving
the pieces, crane operators assembling the bridge, and of course the remaining construction
workers on the job site.
The concrete box-girder bridge alternative addresses many of the needs of the project. ADA
specifications must be followed absolutely for any public work. Fortunately, the concrete box-
girder bridge will stay at a constant elevation throughout its span from its initial launch point off
of the land. There should be no problems in keeping the pedestrian bridge accessible to all
members of the community.
access. The concrete box-girder bridge would be a great addition to the community and to the
admire the eastern span of the SFOBB. Fishermen will also be able to cast lines from the floating
Another way to connect the park and bridge to the community is to hold events. The concrete box-
must serve the community for years to come. The concrete box-girder bridge has a design life of
75 years; what is typically expected for non-critical, non-building structures. Climate change that
results in rising sea levels poses a problem for structures near the ocean. In order to tackle this
problem, the piers will need an additional layer of concrete atop them to ensure they stay above
the king tide not only today, but in the event of sea level rise. Once the tops of the piers are
sufficiently tall, the concrete box-girders can lay atop them and be out of range of the water.
and its history.

20
2.2.6. Alternative 6: Concrete slab-on-piles bridge
Concrete slab bridges are very simple to design and are quite common. The downside of concrete
slab bridges is that they can only span short distances and therefore need many supports. In order
to decrease the span length, piles must be driven beneath the bridge to support it. Driving piles in
the bay comes with many bureaucratic obstacles and can become quite costly.
 Bridge Geometry
and to sit down and spend some time over the water. Rows of 5 piles must be driven into the bay
about every 30 feet longitudinally in order to support the slab.

21
The concrete slab-on-piles bridge additional seismic challenges compared to the other alternatives.
The additional piles that support the slab would transfer ground motion to the bridge deck, almost
certainly resulting in damage to the bridge deck.
Aesthetic details on the concrete slab-on-piles bridge will match the new eastern span of the Bay
Bridge as closely as possible. The bridge will use the same white railings were possible and will
have the same light fixtures and will be located on the piers. The concrete in the bridge can also
be carefully colored to match the color scheme of the bicycle path on the Bay Bridge so that
pedestrians and cyclists can look down from the Bay Bridge and appreciate the matching style.
The concrete slab-on-piles bridge has a very distinct look compared to the SFOBB. The long spans
of the SFOBB are very different from the near-continuously supported look of the pile bridge. One
of the aesthetic benefits to this bridge is that it can be positioned very low on the water, reducing
the visual impact of the piles and
 Purpose & Need
and repurposing the old bridge piers so they don’t need to be removed. Concrete slab-on-piles
bridges are very common with a straightforward design. However, driving piles in the bay is not
as simple as it is on land. There are many regulations on development in the bay and they are quite
stringent. Drilling new piles in the bay would be very difficult to justify for a project this size,
especially given the other alternatives. Even on land, driving piles is an expensive process and
engineers often attempt to use as few as possible. Over the water, the complications are
compounded and costs rise even higher, possibly prohibitively so. However, the other side of this
argument promises a lot of jobs for the community. Casting the concrete deck and piles creates
jobs at a concrete yard, and driving them into the bay must be done carefully with experienced
workers. This requires a lot of equipment, workers, and time, all of which cost money.
The concrete slab-on-piles bridge alternative addresses many of the needs of the project. ADA
specifications must be followed absolutely for any public work. Fortunately, the concrete slab-on-
piles bridge will stay at a constant elevation throughout its span from its initial launch point off of
the land. There should be no problems in keeping the pedestrian bridge accessible to all members
of the community.
access. The concrete slab-on-piles bridge would be a great addition to the community and to the
admire the eastern span of the SFOBB. This type of bridge can also be lower to the water than the
single-span alternatives. The continuous support underneath means that the bridge does not need
to be as deep, so the top of the deck is much closer to the underside of the bridge and the surface
of the bay. This seemingly small change can make a big difference in the feel of the bridge to the
public once they set foot over the water. Fishermen will also be able to cast lines from the floating

22
Another way to connect the park and bridge to the community is to hold events. The concrete box-
must serve the community for years to come. The concrete slab-on-piles bridge has a design life
of 75 years; what is typically expected for non-critical, non-building structures. Climate change
that results in rising sea levels poses a problem for structures near the ocean. In order to tackle this
problem, the piers will need an additional layer of concrete atop them to ensure they stay above
the king tide not only today, but in the event of sea level rise. Once the tops of the piers are
sufficiently tall, the concrete slab-on-piles can span between them and stay out of the tide’s reach.
and its history.
Alternative 6 may be have the most environmental impact on the bay. Driving piles into bay mud
could be damaging to local wildlife in more than a few ways. The process would stir up a lot of
dirt and debris, clouding the water during construction. It would also be extremely noisy, both on
land and in the water, which would certainly be disruptive to aquatic life. It is also important to
note that this almost the opposite of the State of California’s pledge to remove the piers from the
bay; rather than taking out the intrusions, more are placed instead.
2.3 Comparisons of Alternatives’ Characteristics
2.3.1. Funding
The Bay Area Transit Authority (BATA) has allocated approximately $50 million for the removal
of piers E1, E2, and E19-23. The cost of many of these alternatives is considerably less than the
cost of demolition. With the diversion of some of the funds allocated for demolition, BATA and
the state could very realistically save tens of millions of dollars with the additional benefit of
creating a point of public access to the bay.

23
2.3.2. Costs
Each design option, including the no-build alternatives, pile alternative, and no-pile alternatives,
carry different financial costs. Even among each category the costs can vary greatly. Some of the
alternatives are almost prohibitively expensive while others have a much more reasonable price
tag.
The concrete slab-on-pile bridge would be very costly, since hundreds of new foundation piles
would have to be driven in the bay. Driving piles is already expensive on land, but to do so in the
San Francisco Bay, which has countless regulations and complications, would be an unreasonable
expense. Another expensive option is to remove the piers in the bay as originally agreed upon by
the State of California and the BCDC. The controlled demolition that was used for pier E3 was a
very expensive operation. Although it was the biggest pier in the deepest water, removing four
smaller piers would be comparatively exorbitant.
The remaining options are much more financially attractive. Clearly, the no-build alternative that
leaves the piers in the water would have literally zero construction costs. However, leaving the
piers in the water without suitably repurposing them violates the original removal agreement and
Caltrans could face legal action if the piers remain in the water without a suitable purpose. This is
of course highly undesirable for all stakeholders including the state and government agencies.
The other no-pile alternatives are relatively inexpensive. Each option has different costs based on
the complication of design, installation, and overall construction. The precast box girder bridge is
the most expensive of the three since it needs custom formwork for each segment of the box, which
can only be built by skilled carpenters. Then the boxes must be floated on a barge to the job site
and then lifted into place using two cranes operated by experienced workers and supported by
another barge. The pieces are carefully set into place and fixed by crews on the piers. Each step in
this process requires significant manpower and precision.
The concrete I-girder bridge has a comparable construction procedure as the box girder bridge, but
costs a bit less. The transportation and assembly processes are similar to before, with the barges
carrying the girders and the cranes. However, casting the I-girders in the yard is a simpler process.
I-girders are very common and the design requires less detail. Casting yards have molds that can
be endlessly reused to create the necessary-sized I-girder without much trouble. Costs are cut in
the pouring stage because the molds don’t need to be custom built by skilled carpenters.
The most cost-effective alternative is the floating concrete bridge. Although each concrete bridge
is unique and must be carefully sized, most everything else is simple and inexpensive. Materially,
the floating concrete bridge is very economical. The majority of the volume of the bridge is
composed of Styrofoam, much less expensive than structural concrete, in order to create enough
buoyancy in the water. The Styrofoam is of course surrounded by reinforced concrete and has
reinforced diaphragms in the interior, but overall it uses much less structural material since it is
continuously supported by the buoyant force. Additionally, the transportation and assembly is

24
much easier than the girder bridges which span the distance between the piers. Since the concrete
bridge floats by itself, the barge is unnecessary. The pieces can simply be affixed to a tugboat and
pulled to the construction site. Once they have arrived, it is a simple matter of floating them into
place and then fixing them to the piers. No barges, cranes, or other complicated procedures are
needed for the floating concrete bridge.
2.3.3. Constructability & Schedule
All alternatives listed are viable construction alternatives, but some are more practical than others.
The no-build option that leaves the piers in the San Francisco Bay needs no action, and is
essentially already accomplished. However, this option fails to satisfy the regulations governed by
the BCDC and fails to follow through on the promise made by the State of California to restore
the Bay to its former state. The other no-build alternative, removing the piers, certainly requires
more work, as shown during the removal of pier E3, but it follows through on the state’s promise
and is therefore more desirable of the two.
The build alternatives are obviously the more challenging options. The slab-on-piles alternative
requires extensive preparation before any work even begins. Since the slab needs to be supported
by hundreds of piles, this goes completely against the original end-goal of dismantling the old
SFOBB, which is removing man-made obstructions from the bay. Instead of demolishing the old
piers, they not only remain, but even more concrete is inserted into the bay mud. This option carries
significant environmental risk essentially kills it as a viable alternative, since it would basically
never be approved. Aside from the regulatory challenge, it would be quite challenging and time
consuming to drive the hundreds of new piles into the bay.
The no-pile bridge alternatives are more practically constructible because they have minimal
contact with the Bay water and floor. The majority of the work for all three of these options is
done off-site at a concrete yard during the casting of the bridge segments. The piers themselves
need a deeper slab of concrete, must be refinished, and need connections installed where the bridge
will attach, but these processes are well-controlled and should have very little interaction with the
Bay. Assembly should also be fairly quick since the pieces for all three alternatives must only be
set in place—the girder bridges are more challenging but should not cause any greater harm to the
environment than the floating bridge. Each of these designs is practical in their constructability,
but they also intrinsically fail the state’s promise to remove the piers from the bay. The overall
positive impact must be deemed superior to the environmental and political impacts of leaving the
piers in the bay.
2.3.4. Public Access
Both of the no-build alternatives are the least attractive alternatives for the public. Neither option
provides the community with a new location to come together; there is no positive impact for the
public. The no-build alternatives may be economically viable, but they don’t provide any public
access and are more communal blight than boon.

25
Each build alternative will provide a new level of public access to the Bay for the community. The
slab-on-piles bridge and both girder bridges offer essentially the same level of public access. All
of these designs grant the community a new public location to walk out over the water and admire
the San Francisco Bay’s natural beauty. These alternatives also provide an excellent site for
fishermen to settle for an afternoon to try their luck, which has been sorely missing from the East
Bay since the closure of the Berkeley Pier. The space available on these bridge alternatives would
allow the public to hold events out over the water, fostering a growing sense of community for the
area.
The floating concrete bridge rises above all other alternatives in terms of public access. It has all
the features of the out-of-water bridges with some very notable additions. Connecting the
community to the bay is of primary importance to this project. The floating bridge brings members
of the community physically closer to the bay than any other alternative. The underside of the
bridge is obviously in contact with the water and its top barely rises over the surface of the water.
Park patrons could reach over the edge and actually touch the bay water! Additionally, since the
bridge is mostly in the water, waves and tides will move the walking surface. Measures will be
taken to ensure that the bridge does not move too violently, but a gentle rocking will allow
pedestrians to feel the bay’s motion beneath their feet. The proximity to the water also allows water
sport enthusiasts an easy access point to explore the bay as a whole. Since the bridge surface is so
close to that of the water, kayakers, windsurfers, and their ilk could launch right off the bridge. A
simple gate or a removable section of barrier is all that is needed to create an aquatic activity hub.
For all these reasons, the floating concrete bridge alternative clearly provides the greatest public
access.
2.3.5. History
The San Francisco Bay Area is rich with history and importance that influenced not only
California, but also the United States its connection with the rest of the Pacific Rim. The old
SFOBB was envisioned during California’s formulation during the Gold Rush but would not be
built until the 1930s. The SFOBB represents the economic and political growth of the Bay Area
and California as a whole and the attitude and stick-to-itiveness of the people who lived and died
in this wonderful land. Preserving a piece of the old SFOBB would serve as an educational and
cultural landmark to the hard work and perseverance of our state and residents.
The no-build alternatives both do very little to pay homage to our history. By destroying these four
piers, the last of the SFOBB would be permanently removed from the bay without a visible trace
and leaving the piers in the water without access is almost as dismissive. Providing pedestrian
access out to the piers is a better way to honor and preserve the past.
Each of the build alternatives can be an equally effective monument to the old SFOBB. Atop each
pier currently stand two pedestals that supported the superstructure of the bridge. All of these
alternatives will leave the pedestals intact and thicken the floor slab surrounding them. There is

26
plenty of room on the piers to mount plaques bearing information about the history of the region
and the motivation for building the original bridge. These pedestals could also educate the public
on basic engineering principles. By allowing people to come in contact with these pedestals, they
can appreciate the enormous scale of infrastructure that they often take for granted. It could also
provide perspective on the challenges that the constructing workers and engineers faced almost
one hundred years ago when designing and building such an ambitious structure. As the Bay Area
continues to develop, it is important to have a window into the past to as a reminder of our
challenges faced and our ability to overcome them.
2.3.6. Climate Change & Sea Level Rise
One of the most significant challenges facing coastal development is the threat of climate change
and future sea-level rise. Oceans are predicted to rise by as much as 55 inches in by the end of the
21st
century (BCDC 2015). Any coastal structures with lifetimes comparable to this time frame
must come equipped to deal with rising sea-levels. The alternatives outlined here have varying
capability of dealing with climate change and rising tides.
The floating concrete bridge is clearly the most capable of dealing with changes in sea level. The
bridge is already designed to not be permanently affixed to the supporting piers and to rise and fall
with the tides. Among the very few measures needed is to increase the height of the piers to
outreach the future sea-level height increase. The slab on top of these piers must already be
heightened since the bay waters rise a few inches above the top during king tides. By adding an
additional five feet to the top of the piers, the walking surface will remain above water not only
during today’s king tides, but also for those predicted by the end of the century. The other
important measure is increasing vertical size of the shear key holding the floating bridge in place.
This is a simple measure that prevents rising oceans from pushing the floating bridge up over the
shear keys, which would cause it to float off into the bay. Increasing the pier height by five feet
instead of a few inches and building larger sheer keys requires more labor and construction
materials, but lengthens the pedestrian-accessible service life of the piers approximately to the year
2100.
The precast box-girder bridge and I-girder bridge do not have the same natural adaptive advantage
as the floating bridge, but similar measures can be taken to protect them from sea-level rise.
Compared to the floating bridge, the piers need an additional height increase to keep the tops above
future high tides, but must be even higher if the bottoms of the girders are to remain above the sea-
level. Then, the precast sections can be lain, spanning between the piers, several feet above the
current water level. As long as the initial height is sufficient, the precast bridges should be well-
equipped to deal with sea-level rise.
The concrete slab-on-piles bridge requires additional efforts on top of those for the precast bridges.
The pier must be raised to account for rising sea-level, high enough to keep the bottom of the slab
out of the water. Additionally, each individual pile has to rise that far out of the water. The
increased heights of all these piles results in a significant increase in material and financial cost
for this alternative. On top of these costs, the bridge would rise over five feet out of the water at

27
the time of construction. This would give it an awkward, stilt-like appearance. Next to the beautiful
new SFOBB, it would be a complete eyesore.
Finally, there are the two no-build alternatives. Sea-level rise is entirely irrelevant for the pier-
removal option, but could be problematic if the piers remain. Since the piers currently get
covered by a few inches of water during king tide, if they were to remain as oceans rise, the tops
would become constantly covered. This would eliminate the unpleasant sight of them, but would
be extremely hazardous to boats, kayaks, and other bay activities as invisible, barely submerged
obstacles.
2.3.7. Environmental Impact/Advantages
Every construction project has, at the very least, an effect on the local environment. For
construction over water, these effects typically carry even greater impact. Many of the build
alternatives use as many precast elements as possible in order to minimize concrete poured on site
and shift some of the impact to a concrete casting yard instead of the bay waters.
Conversely, several of these alternatives have the option to create one or two small bird sanctuaries
on the piers. Each pier that is left in the water that does not have pedestrian access could be
specially engineered to serve as a bird nesting habitat. Far from the shore, these piers are isolated
from the land and are model nesting sites, protected from terrestrial ovivorous (egg-eating)
animals. The opportunity for inexpensive bird sanctuaries left on the piers offsets some of the
potential environmental harm resulting from leaving the piers or construction over the bay.
Of the build alternatives, the slab-on-piles bridge would be most detrimental to the environment.
Even though the slab and piles would be cast off-site, this alternative disrupts the bay more than
any other. The slab-on-piles bridge needs hundreds of piles driven into the bay mud, which would
greatly disturb aquatic life by churning up dirt and debris and with the deafening clatter of a pile
driver. This alternative also completely goes against the state’s original pledge to remove the man-
made remnant piers of the old bridge and instead adds more piles.
The remaining build alternatives each have roughly the same environmental impact. The floating
concrete bridge, the concrete box-girder bridge, and the concrete I-girder bridge have very similar
building requirements. They each need the piers to be raised several feet, which will require a
construction crew to pour concrete directly on the piers. This process carries risk of pouring
concrete into the bay water due to its immediate proximity. Each of these alternatives also needs a
way to hold the bridge in place, be it a shear key for the floating concrete bridge or a seat-type
abutment for the girder bridges. These pieces would likely be cast off-site and carefully affixed to
the augmented piers. The shear key will need to be set in place and bonded to the pier using
cementitious material, again carrying the risk of spillage into the bay.
The no-build, do nothing alternative that leaves the piers in the bay still has a significant impact
on the environment. Despite this option not requiring any construction or demolition, it is in direct
violation of the state’s pledge to remove the remnants of the old bridge from the bay. Even though

28
nothing new is added in this option, the piers are still man-made, foreign objects in an
environmentally protected area. Additionally, the remaining piers protruding from the water could
be a bit of a blight on the otherwise beautify bay.
The no-build alternative that removes the existing piers from the bay does the most to restore the
bay to its original state. This alternative also follows through on the state’s original commitment
to clear all the piers from the bay after the completion of the new eastern span. This is the only
alternative that purely works towards returning the bay to its virginal, unspoiled state.
2.3.8. Economic Stimulus/Jobs
A project’s effect on the local economy can be one of the most important avenues to its approval.
Local jobs and local spending are very attractive to communities and to their local politicians who
can espouse the advantages and success of the project. The best projects are both competitively
priced and large employers to the local community.
Each of the build alternatives would stimulate the local economy and provide jobs for the
community. The vast majority of the concrete work can be done off-site in a casting yard. Some
of these yards employ up to hundreds of skilled laborers working on various projects throughout
the community. The floating bridge and the box girder bridges all require great amounts of
materials and many workers to complete the job in an adequate time frame. These three alternatives
have many similar economic advantages to each other and should be quite attractive to politicians
and local workers.
The no-build, pier removal option also provides work to the community. Although it does not
require any construction or new materials, the task of removing the piers is complicated,
dangerous, and requires highly-skilled, highly-trained workers. Pier E3 was carefully removed
using a controlled implosion set into motion by several divers who fixed carefully placed
explosives along the pier’s submerged surface. This delicate operation does not employ as many
people as construction would, but still provides jobs to the community and injects money into the
local economy.
The no-build, do nothing alternative clearly falls short of all other alternatives from an economic
perspective. No money moves to material suppliers or construction employers when there is no
work to be done. There is really political or economic advantage to the do nothing alternative.
2.4 Selecting a Preferred Alternative
After weighing many factors, including financial costs, funding, constructability, erection time,
ability to address the purpose and need of the project, and environmental impact, the floating
concrete bridge (Alternative 3) was selected as the Preferred Alternative. Table 2.1 illustrates how
the strengths and weaknesses of each alternative was weighed and quantified.

29
Alternatives
No build
Pile
alternatives
No pile alternatives
Leave
piers
Remove
piers per
original EIR
Slab-on-
piles
concrete
bridge
Precast I-
girder
bridge
Precast
box girder
bridge
Floating
concrete
bridge
Public Access -1 -1 2 2 2 3
Historic Preservation -1 -1 2 2 2 2
Climate change/rising
ocean preparedness
N/A N/A 1 1 1 2
Financial Cost 2 -2 -2 2 1 3
Completing original EIR
commitment
-2 2 -2 -1 -1 -1
Schedule -2 1 -2 -1 -1 -1
Risk -1 1 -2 0 0 0
Architecture/Communit
y experience
-1 1 -1 1 1 2
Fill in the Bay -1 2 -2 -1 -1 -1
Bird habitat/ sanctuary 1 -1 1 1 1 1
Jobs -1 1 2 2 2 2
Total -7 3 -3 8 7 12
Table 2.1

30
2.5 Construction Process of the Preferred Alternative
The floating concrete bridge alternative has many steps in the construction process. Here is a broad
overview of the construction plan:
 Prepare the tops of existing piers for heightening and resurfacing
 Pour the new, raised surface of the piers
 Begin offsite casting of concrete shear keys to hold spans
 Prepare piers for shear key installation (bores in the sides of the piers for shear key
attachment)
 Begin offsite casting of floating concrete spans
 Bring half of the shear keys to jobsite, fit them to the piers, and attach using cement paste
 Float the bridge from the casting yard down to the jobsite and slide into place
 Attach the other half of the shear keys, locking the floating bridge in place
 Install ADA compliant ramp connecting the piers to the bridge decks
 Install railings and apply aesthetic touches
 Building substructure of the bridge
 Traffic closures and diversion during erection of temporary framework
 Pour concrete for superstructure of bridge and apply prestressing
 Traffic closures and diversion during removal of temporary framework
Each stage must be carefully coordinated and timed to ensure the least amount of downtime as
possible. Transporting structural elements from the concrete yard via tug boat may require
arrangements with the coast guard or tariffs paid to the local regulatory agency. Construction over
the bay must follow all BCDC regulations, restrictions, and requirements unless otherwise
exempted.
Full Construction Staging of Preferred Alternative
Alternative 3 is an unconventional design for a bridge, but it has some similarities to floating
concrete docks used in marinas. The bridge is made of reinforced concrete encasing a foam
interior, which causes it to float. This design is on a much larger scale compared to floating docks
and has two interior “girders” which increase the flexural rigidity of the bridge. With these
uncommon design considerations, the instructions in this design must be carefully followed to
ensure that the bridge remains safe and strong. The following are the longer, more detailed steps
in constructing the floating concrete bridge:
1. Prepare the tops of piers for the increase in height by scouring off the exposed concrete that has
been worn by weather effects. Bore vertical holes in the concrete that will serve as splice points for
the new pier tops.
2. Place rebar in the newly bored holes on top of the pier and pour the new surface of the piers, five
feet higher than the old surface. The rebar in the bores should splice the old and new concrete
together. Leave horizontal holes on the sides of the pier where the shear keys will splice in.

31
3. In a casting yard, construct wood formwork for shear keys that will restrain lateral movement of
the bridge but allow for vertical movement.
4. Place rebar in the shear key formwork and pour the concrete Allow concrete to cure up to strength.
5. Prepare the piers for shear key attachment. Bore horizontal holes in the portion of the pier where
the shear keys will splice in. Build formwork that keeps water off of the area that will receive the
shear key.
6. In a casting yard, begin construction of the floating concrete bridge. Shape the interior foam into
three pieces, each 248 feet long, 104 inches wide, and 66 inches tall.
7. Place structural reinforcing bars around and between the foam in the T-shape that the concrete will
take. Reinforcing bars should also be in the “girders” between the foam blocks and outside the foam
blocks; each foam block should have reinforcement surrounding it on all sides except for the
bottom. (Figure 2.1)
Figure 2.1

32
8. Build formwork for the floating concrete bridge around the existing foam and rebar (Figure 2.2)
Figure 2.2
9. Cast lightweight concrete around the foam blocks, over the rebar and finish the surface. (Figure
2.3)
Figure 2.3

33
10. Steam cure the concrete bridge under cover to expedite strengthening process. (Figure 2.4)
Figure 2.4
11. Once the shear keys have cured, transport them to the job site.
12. Attach shear keys on one side using the splice holes in the pier and fill them with cementitious
material.
13. After the concrete bridge has cured, apply rubber or wood padding around the top edges to reduce
impact between the bridge and the piers
14. Using a crate, hoist the floating concrete bridges into the water or onto a barge. (Figure 2.5)
Figure 2.5

34
15. Tug concrete bridges down to the job site, and float them into place.
16. Attach the other half of the shear keys, locking the bridge in place.
17. Attach railings to the sides of the bridge deck and to the sides of the piers
18. Attach the rotating ramps to the piers and allow them to run onto the bridge decks.
19. Apply finishing architectural touches to the piers and bridges.
20. Install lights and other electrical features on the piers.
21. Install any bench seating, binoculars, and or/plaques.
22. Clean up the job site and open up for the public!
2.6 Bridge or Barge?
One may ask if the floating concrete bridge is actually a bridge. After all, it floats on the water
rather than spanning the distance. Some might say it is more barge or dock than bridge, and it is
therefore important to refute this notion immediately. The floating concrete bridge is a very real
structure that meets bridge design codes. It is not a cheap dock that will fall apart in a few years.
This bridge has a 75 year design life and is capable of supporting thousands of pedestrians and a
15 ton trick simultaneously. All strength and loading calculations for the bridge include factors
of safety to ensure that the bridge can handle anything thrown at it. A barge tied between two
piers would rust quickly, drift significantly, and be very unsafe. A barge has no structural design
requirements and could not endure nearly the magnitude and frequency of loading that the bridge
can.

Chapter 3: Loading Demands
35
CHAPTER 3: LOADING DEMANDS
3.1 Vertical Loads
The floating concrete bridge is designed as a pedestrian walkway out over the bay. It should be
capable of supporting large numbers of pedestrians and the occasional maintenance truck.
AASHTO prescribes a pedestrian loading of 85psf over the area where people are allowed to walk.
This bridge has been designed with additional capacity in mind at 100psf in case of accidental
overloading during special events or even crises. The maintenance truck used in design is an H-15
truck weighing 24 kips on the rear axle and 6 kips on the front axle. To prevent disaster, these
loads are applied in a variety of configurations and orientations in an attempt to create a “worst-
case scenario” that loads the bridge as severely as possible. These loading scenarios could all be
run simultaneously and analyzed with a three-dimensional model or projected into two dimensions
and run in two two-dimensional models. This bridge was analyzed using the latter method with a
longitudinal model and a lateral model.
3.1.1 Load Paths
It is very important to understand the load path of a structure during design. The engineer must
know how the forces move through the structure in order to effectively size and link structural
components. A typical deck-on-girders bridge designed to carry vehicular traffic has a simple load
path that generally progress down the structure. The begins in a vehicle, goes through the tires,
loads the deck, then loads the girders, then that is passed to an abutment or bent, then down to the
foundation and piles, which finally transfers it to the ground. A simple diagram numbering the
steps is shown below in Figure 3.1.
Figure 3.1

36
The floating concrete bridge has a different load path that is slightly shorter. The loads begin the
same, starting with the truck, then to the tires, then onto the deck. The load path begins to diverge
here by sending the forces into the girders and the foam between the girders alike, and then the
load goes into the water where the bridge is held up by the buoyant force. The numbered load path
is shown below in Figure 3.2. The way the loads are distributed into the girders and the foam
together greatly reduce the moments and shears in the girders. The buoyant force acts along the
entire underside of the bridge exactly matching the downward loads.
Figure 3.2
3.1.2. Longitudinal Loading Configurations
There are eight different loading configurations for the longitudinal model. Some include only
pedestrian loads and some include both the pedestrian and truck loads. Trucks and pedestrians are
placed in an attempt to create the worst possible loading conditions for the bridge. In a few of these
load cases, the trucks are on the very far edges of the bridge in an attempt to create the largest
moment for a continuously supported beam. Also, some of these loading situations will actually
not be permitted in reality, like a truck load superimposed over the pedestrian load. These cases
are included mostly as a thought experiment, but can also be realized in the event that people
decide to ignore the temporary barriers set up during maintenance and walk too close to the
maintenance truck. Below are the eight loading configurations analyzed in the longitudinal model.

37
Figure 3.3

38
3.1.3. Transverse Loading Configurations
There are six different loading configurations for the transverse model. Some include only
pedestrian loads and some include both the pedestrian and truck loads. Some of these loading
configurations are designed to induce moments of opposite signs over the transverse length of the
deck to ensure the deck can deflect in both vertical directions. Included are load cases that have
with pedestrians all the way to the edge of the deck, and some stop just over the outermost girder.
The transverse model analyzes a segment of deck that is 16 feet deep, which is wide enough to fit
the entire H-15 truck which has axles 14 feet apart. Below are the six loading configurations
analyzed in the transverse model.
Figure 3.4

39
3.2 Lateral Loading Considerations
3.2.1. Seismic Loading
The floating concrete bridge has a very different seismic response than the other bridge alternatives
outlined previously. All of the other alternatives were supported entirely by the piers or supported
by the piers in conjunction with interior piles. The floating bridge, however, is different in that it
is continuously supported by the water. For the case of the floating bridge, the piers’ only job is to
keep the bridge from floating off into the bay; they only restrain motion in the horizontal directions,
not in the vertical direction. Essentially, there is no real fixity between the floating bridge and the
piers. The bridge basically just slides into place and is kept in the proper location with concrete
shear keys covered with a layer of wood or rubber to reduce collision impact forces. This type of
“connection” is very helpful when considering the seismic response of the structure.
Since the bridge is continuously supported by water and basically detached from the piers, the
seismic loading on the bridge can be ignored. Without a rigid connection, there is no load path for
the earthquake forces to reach the floating concrete bridge. During an earthquake, many different
types of waves are produced and propagate either through the interior of the Earth (body waves)
or along the surface of the Earth (surface waves). There are two types of body waves, the Primary
wave, or P-wave, which travels more quickly, and the Secondary wave, or S-wave, which is a
transverse shear wave that is slower and more destructive. The two basic types of surface waves
are Rayleigh waves, or “ground roll,” which cause solids to roll and ripple like the surface of a
fluid, and Love waves, which are a horizontal shear wave. What is most important to note, is that
the only type of seismic wave that the bridge can feel is the least destructive of them all, the P-
wave. Rayleigh waves can be extremely damaging, but cannot effectively propagate through
fluids. S-waves and Love waves can also be very destructive, but these are both types of shear
waves, and water, of course, cannot sustain or transmit and shear force at all.
The fundamental feature of the floating concrete bridge perfectly shields it from the most
destructive aspects of earthquakes. Floating in a fluid protects the bridge from all of the most
destructive seismic waves, the roll action and shear action. Therefore, there is no need to run a
seismic analysis on the floating concrete bridge.
Conversely, the piers do feel seismic forces because their foundations are fixed deep in the mud,
sand, gravel, clay, and rock beneath the bay floor. The piers will shake and deflect under
earthquake loads, but there is no need to worry about them. The remaining substructure was
previously designed to hold the weight of the superstructure, ten traffic lanes full of cars, and a
train load. Since the mass of the structure is so severely reduced, the ground accelerations will not
produce nearly the same force that they would have previously. Therefore, the piers are
considerably overdesigned for the magnitude of forces that they would likely receive during the
next design life. Due to these advantages, seismic forces do not control the design on the piers.

40
3.2.2. Wave Loading
The main lateral load on the floating concrete bridge will come from the ebb and flow of tidal
currents and waves crashing against the side. For an initial calculation, the drag equation
determines the magnitude of the lateral forces acting on the bridge.
Equation 3.1
Here FD is the drag force, ρ is the mass density of the fluid, A is the area of the face over which
the fluid flows, CD is the drag coefficient of the face the fluid flows over and is based on the
geometry and orientation, and v is the velocity of the fluid flow. Using a fluid velocity of 3 knots,
very high for the bay, especially so close to the shore, and considering two surfaces, the underside
of the bridge and the “front” face where the incoming water is orthogonally incident (which would
create the largest loads), the total drag force on the entire body is calculated at about 55.5 kips.
Then that load can be divided along the length of the bridge to get a continuous distributed load of
about 0.226 kip/ft. From here, the bridge can be modeled as a simply supported beam with a
distributed load. What is “vertical” here is really the “lateral” load coming from the waves. This
load is very minor compared to the vertical loads and the existing reinforcement is more than
sufficient to keep lateral deflections and cracks under control.
Figure 3.5

41
Using only this drag force equation is a huge simplification. In reality, there could be many more
factors adding greater stresses on the bridge. One of the spans comes out from the shore, so there
is very little water flowing beneath the underside, at least on one side. This situation may result in
a quasi-damming behavior that accumulates more water on the side from which the water, resulting
in hydrostatic forces on one side of the bridge. Additionally, the span closer to the shore may even
bottom out in the shallow water during low tides. This would send all the water flow around to
where the floor is deeper, creating unpredictable flows. These could be major concerns, but it is
impossible to say without more information. Before any designs are made final and any
construction takes place, further on-site studies may be necessary and additional lab sensitivity
studies would also be prudent.

Chapter 4: Design and Calculations
42
CHAPTER 4: DESIGN AND CALCULATIONS
4.1 Design
The floating concrete box pedestrian bridge is modeled in SAP2000 using two models—a
transverse model and a longitudinal model. Together, these models tell the full, three-dimensional
story of the bridge and accurately analyze the structure. The effects of the dead load uniformly
sink the bridge into the water, while the various live loads induce greater stresses and deflections.
The following design successfully satisfies the strength requirements of the bridge based on the
vertical dead and live loads and the lateral wave loads. Several architectural renderings of the
design can be found in the appendix.
The materials used in the bridge are common and readily available. All the concrete in the bridge
is sand-lightweight 5000 psi concrete to keep the section as buoyant as possible. All steel
reinforcement will be epoxy-coated 60 ksi steel to provide sufficient strength and corrosion
resistance. The expanded polystyrene (EPS) will be EPS29, a common, sturdy, lightweight plastic
material manufactured to meet ASTM D6817, “Standard Specification for Rigid, Cellular
Polystyrene Geofoam.” EPS29 has a compressive resistance of about 10.9 psi and a modulus of
elasticity of 1090 psi. These physical properties should not come into play, however, since the
entirety of the load is carried by the steel and concrete.
4.1.1. Floating Box Design - Longitudinal
Piers E23, E22, and E21 are all equally spaced at 292 feet apart center-to-center and are 44 feet
wide. The full job requires two identical bridges, each 248 feet long with a 30 foot wide top deck
that is 6 inches deep. The deck of the bridge has an overhang that extends 16 inches over the
outside of the girders, making the width of the foam and girder section a total of 27 feet 4 inches.
There are three 4-inch girders in the bridge 108 inches apart center-to-center, each 4 inches thick,
extending 66 deep. The bridge uses #8, #6, and #4 bars for different steel reinforcement. The
longitudinal reinforcement in the deck are #8 bars and have a clear cover of 2.5 inches from the
top and are spaced 8 inches apart. The girders contain #6 bars and #8 bars with different spacing.
The bottom 33 inches of the girder have #8 bars spaced 4 inches apart with 2 inch cover on all
sides. The top 33 inches contain #6 bars spaced 6 inches apart with 2 inch cover on the sides. The
space between the girders is filled with expanded polystyrene geofoam to displace water and create
a buoyant force that keeps the deck above water. The foam is entirely enclosed by the girders on
the sides and by a thin layer of cementitious material over fiberglass mesh to keep water out.
The bridge will be constructed off-site in a concrete yard with access to water that connects to the
bay. Each 248 foot span will be constructed as one piece so that no on-site assembly is required to

Chapter 4: Design and Calculations
43
finish the bridge. Once cast in the yard, the bridge can float all the way to the site and simply slide
into place.
Figure 4.1
4.1.2. Floating Box Design – Transverse
The transverse reinforcement in the deck must support an H-15 truck load and pedestrian load in
almost any combination. There are two sets of transverse #4 bars in the deck to handle both
negative and positive moments. They have a clear cover of 2 inches from the top of the deck and
2 inches from the bottom of the deck and are both spaced 8 inches apart. For shear reinforcement
in the girders, alternating lower level of deck bars bend down from the deck into the outer edge
of the exterior girders making a U-shape. Since every other bar in the bottom transverse
reinforcement goes into the girders, the spacing is 16 inches. The interior girders will have
vertical #4 bars as well, but these ones are simply tied into the transverse reinforcement, not
continuous, bent bars. The #4 bars run down to the bottom layer of #8 bars in the girders as
shown in the figure below.

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