Princeton University - Council of Science & Technology

POPE PRIZE

Essay 1
Losing the Race Against Time: Rebuilding the San Francisco-Oakland Bay Bridge
Christi C. Niehans

Essay 2
Chemical Weapons Burn in Arkansas
Brian D. Muegge

Essay 3
Mann's History
Melissa M. Galvez

Essays 4
Postpartum Cases: Tadoka and Mental Health
Amy B. Saltzman

Honorable Mention
Julia B. Saltz

Losing the Race Against Time: Rebuilding the San Francisco-Oakland Bay Bridge

During rush hour on October 17, 1989, the Loma Prieta earthquake collapsed a fifty-foot section of roadway deck on the ten-lane Bay Bridge connecting San Francisco to Oakland, California. The entire nation knew almost immediately, because a Goodyear blimp was nearby to broadcast Game One of the World Series between the San Francisco Giants and the Oakland A’s, aptly referred to as the “Bay Bridge Series.” The vital transportation artery was reopened to traffic after 32 days of repairs, but a survey of conducted by the California Department of Transportation (Caltrans) concluded that any retrofit would be extremely costly and inadequate to make the East Span of the Bay Bridge seismically sound. Thus began a “race against time” to design and build a new bridge before the next major earthquake. More than 15 years have passed, and the Bay Bridge is again making news because completion of a replacement span is now expected to take at least another seven years. Meanwhile, 275,000 vehicles cross an unsafe bridge each day. The most recent studies by the United States Geological Service indicate that there is a 62 percent chance of an earthquake of magnitude 6.7 or greater occurring in the San Francisco Bay area between the years 2003 and 2032.1 Given the Bay Bridge’s location directly between the two largest and most active faults in the area, the damage caused by another earthquake could easily exceed that suffered in 1989, which resulted from a quake on a relatively minor fault epicentered 60 miles away from the bridge. Due to a combination of technical and political challenges, we may be losing the race against time. Immense Technical Challenges Although always overshadowed by the greater glamour of its sister, the Golden Gate Bridge, the current Bay Bridge has always been recognized as a marvel of civil engineering. Even taking advantage of Yerba Buena Island, a small rise of shale rock midway between the shores of San Francisco and Oakland, there remain two sections of water, each nearly two miles wide. The water is over a hundred feet deep in places, and the underlying Bay mud is deep and unstable. When finished in 1936, the 4.36-mile2 Bay Bridge was the longest steel highlevel bridge in the world3 and the most expensive civil engineering project ever built. But considering both length and number of lanes, it was six times more economical than the George Washington Bridge that joined New Jersey and Manhattan five years earlier. Twenty years later, the American Society of Civil Engineers named the Bay Bridge one of the “seven engineering wonders of the world.”4 Despite the inability of one of its spans to meet current seismic safety standards, the original bridge was a monumental achievement, incorporating innovative and economical design and construction techniques brilliantly tailored to the uniquely challenging site conditions. The East span replacement project is demonstrating that the challenges posed by bridging the Bay are no less difficult today: The East side of Yerba Buena Island will not support a suspension cable; the Island’s bedrock drops off sharply toward the deepwater channel; and the Bay mud beneath the entire span makes the construction of piers extremely expensive. The goal of reconstruction, therefore, should be to employ modern bridge technologies that allow today’s engineers to solve these problems with elegance and efficiency. A Modern Political Quagmire Few engineers, politicians, or citizens disagree with the decision by the California Department of Transportation to replace the East span of the Bay Bridge after the Loma Prieta earthquake. That, however, seems to be the only uncontroversial bridge-related decision that the State of California and its agencies have made since the disaster. Caltrans’ first mistake was to begin the design process in-house. Its engineers are very experienced at building overpasses and on-ramps, but have little knowledge of long span bridges. In 1996, Caltrans engineers presented two preliminary designs. The first was a towerless 2.2-mile causeway euphemistically referred to as the “skyway.” The second was a skyway with a rather ungainly cable-stayed span whose two sideby- side A-frame towers each straddled a five-lane deck.5 Caltrans publicized the merits of the skyway, highlighting its simple elegance and smaller price tag. (In late 1996, Caltrans estimated that the skyway would cost $1 billion.)6 But when sketches were published in local newspapers, there was an immediate outcry from politicians, citizens, and designers. Some accused the design of resembling a two-mile-long freeway onramp, while several of the more constructive critics called for an open and juried international design competition.7 Concerned with aesthetics, none focused on the fact that the designs were fundamentally inappropriate for the site. The deep, unstable Bay mud makes it very expensive to build piers, and the short, heavy sections of concrete skyway would require dozens of them. Moreover, the longest span proposed using concrete skyway technology would narrow the existing navigation channel by nearly fifty percent— from 1,164 feet to 640 feet.8 Rather than selecting a qualified jury and hosting a design competition, the State committed its second error: passing legislation that gave the Metropolitan Transportation Commission (MTC) authority to choose the new bridge design.9 The Commission is the Bay Area’s transportation planning, financing, and coordinating agency, composed of elected officials charged with such tasks as developing pothole prevention plans and extending carpool lanes.10 Replacing one of the “seven engineering wonders of the world” was well beyond its scope of expertise. Sunne McPeak is California’s new Secretary of Business, Transportation and Housing. Appointed by Governor Schwarzenegger in November of 2003, she oversees 16 departments, including Caltrans. When asked about bridge-building experience, she stated: “MTC has no members with any experience. If you can find one, point him out to me. They have nobody. Within MTC, its 19 members, its employed staff, [they] have no experience in building bridges.”11 The Metropolitan Transportation Commission assembled the Bay Bridge Design Task Force— composed of seven elected commissioners—and the Engineering and Design Advisory Panel. The Advisory Panel included thirty-five architects, engineers, and Caltrans advisors.12 The Metropolitan Transportation Commission announced that the Engineering and Design Advisory Panel would hear presentations and review six-page design submissions on three days during mid-May, 1997. After inquiries at the end of April revealed that there was neither an established submittal process nor design criteria, the Commission finally published them on April 30, giving interested parties only twelve days to prepare. The responses were pre-screened, and the majority of the presentations were made by members of the Advisory Panel, including one that exceeded the length limit by 94 pages. In fact, more than half of the members of the Advisory Panel were involved in one or more submittals, preventing the jury from being impartial.13 Ideas ranged from Victorian and floating bridges to cable-stayed and self-anchored suspension spans. Jerry Brown, Oakland’s Mayor, argued for a continuous span across the Bay, with no skyway.14 Historically, Oakland has been an industrial city, living in the shadow of San Francisco’s business district and famous skyline. In recent years, however, Oakland has invigorated its economy by maintaining state-of-the-art shipping terminals and attracting hightechnology businesses. As the existing cantilevered truss of the East span has reinforced Oakland’s plebian image, Mayor Brown’s hope was that the new bridge would extend San Francisco’s elegance to the opposite shore and better reflect 21st-century Oakland. The Advisory Panel rejected Caltrans’ idea of a simple skyway at the outset due to its unfavorable public reception, but it quickly decided to use it as a template on which to superimpose a “signature span” with a single tower founded in the bedrock near Yerba Buena.15 Within days of the presentations, the Advisory Panel dismissed all ideas not originating from Panel members, with the exception of a cablestayed “sail” proposed by Professors Gary Black and Abolhassan Astaneh of the University of California, Berkeley.16 All designs submitted by Panel members were retained for further consideration.17 At least one rejected team protested in writing, stating: “It seems we were invited to submit a proposal only to give apparent legitimacy to an illegitimate process.”18 By late June, it appeared that not even the members of the Advisory Panel themselves agreed on the appropriateness of the selection process. While the Panel recommended that three designs be developed to 30 percent, the chair, Joseph Nicoletti, and vice chair, John Kriken, submitted separate reports to the Metropolitan Transportation Commission: Nicoletti recommended that the Panel members’ entries be further investigated, while Kriken suggested “something along the lines of a short, effective competition.”19 Instead, a small committee of engineers from the Advisory Panel met in private in July. Without the benefit of input from the other members of the Panel, they eliminated the “sail” design and also chose the alignment of the bridge. This placed the new span north of the existing one and located the tower dangerously close to the Temescal formation, an ancient river canyon beneath the Bay.20 The only decision remaining was whether the western portion of the bridge would be a cable-stayed or self-anchored suspension span. Rather than putting the brakes on what many viewed as an insider selection process, the Legislature adopted the Engineering and Design Advisory Panel’s findings by passing Senate Bill 60 in August 1997.21 While leaving the details of the final bridge form up to the Metropolitan Transportation Commission, SB60 stipulated: “the main span of the bridge will be in the form of a single tower cable suspension design.” It also specified that the new span would be built to the North of the existing bridge.22 Because it severely limited future design flexibility, expressly mandating the bridge form and location in legislation was a third grave mistake. Despite continuing demands for a design competition23 and irrespective of MTC’s request to Caltrans for permission to hire two firms to further develop ideas,24 Caltrans unilaterally awarded a contract to TY Lin International for the development of four designs, all of which were to superimpose a signature span onto the skyway.25 (T.Y. Lin himself is no longer affiliated with the company that bears his name.) In the midst of this process, soundings taken in the Bay confirmed that the Temescal formation would require shifting the bridge South, which required shortening the signature span and moving its tower away from Yerba Buena Island and into the shipping channel. The revised location placed the tower not on the solid bedrock offered by Yerba Buena, but in the deep Bay mud beyond.26 The technical motivations for superimposing a single signature span onto a skyway had been to place the main tower in the available bedrock of Yerba Buena and to provide a wide navigable channel through the deepest part of the Bay. But the necessary shift in bridge alignment negated these driving factors. Indeed, the resulting signature span would be shorter than the existing cantilever built in 1936.27 Retaining the same design meant that the bridge had lost its inherent logic and was no longer at all tailored to the site. But other options were never revisited with the benefit of new information, and alternatives to the skyway portion of the bridge were never seriously considered. Instead, throughout April and May of 1998, Caltrans published images of the four alternative signature spans. Although a single company was responsible for all of them, the State created the illusion of a competition.28 Opportunity Lost Although T.Y. Lin himself never wavered in his conviction that a cable-stayed span was the best solution for the site, many other committee members believed that a cable-stayed bridge with a sufficient span would require too tall a tower and risked overpowering Yerba Buena and the neighboring bridges. They also disliked the symmetry suggested by the cable-stayed span. On the last day of discussions it was, surprisingly, an engineer who persuaded the panel that a selfanchored suspension span would have a lighter feeling than a cable-stayed bridge, due to the curvature of the main cables and their shape’s apparent independence from gravity.29 The fact that the catenary shape of a suspension cable is due entirely to the forces of gravity acting upon it was overlooked. And the thicker deck required by the tremendous compressive stresses caused by the selfanchored suspension cables must not have been factored into the panel’s assessment of lightness. Unfortunately, no one explored the possibility of making a cable-stayed bridge asymmetrical simply by weighting the shorter end and shortening its horizontal cable spacing, making the cable layout one cable per unit weight of deck instead of one cable per unit length of deck. The Panel also failed to appreciate the inherent beauty of being able to see from a structure’s form exactly how it is supported. A cable-stayed bridge is a perfect example of structural art: determinate, efficient, and logical. A self-anchored suspension bridge, however, resembles a person trying to lift himself up by his own bootstraps: the deck is held up by the cables, which are in turn anchored to the deck they are supporting. Construction is necessarily a slow and expensive process, requiring the entire bridge deck to be built on temporary scaffolding, then the cables attached, and finally the supporting falsework removed. The Advisory Panel was aware that the self-anchored suspension design would be more expensive than the alternatives, including a cable-stayed span.30 Yet on May 29, 1998, with only nineteen of 35 members present, it voted twelve to five in favor of the single-tower self-anchored suspension bridge and delivered its recommendation to the Metropolitan Transportation Commission. Despite continued public objections to the bridge design and its selection process, the Commission approved the skyway and self-anchored-suspension span on June 24, 1998.31 The East span replacement project represented an opportunity for the Bay Area to combine today’s technology with the innovation, daring, and resolve that characterized the first Bay crossing. The new bridge had the potential to be not only a new Bay Area icon, but also another engineering masterpiece that would be marveled at for centuries: a bridge to which all future bridges would be compared. Yet none of the designs considered explored this possibility. Some submissions showed originality, like Black and Astaneh’s “sail.” Others, like T.Y. Lin’s cablestayed design, demonstrated some sound and practical engineering. The self-anchored suspension proposal offered a new chapter in the Bay Area’s history of suspension bridges, but one lacking both technical and economic efficiency. No design considered truly suggested inspiration. The greatest error committed in the long selection process for the new East span of the Bay Bridge was the failure hold a juried design competition and give the world’s best bridge engineers a chance to compete for the opportunity to design the perfect span for one of the world’s most complex and beautiful locations. When approved in June of 1998, the East span replacement was scheduled to be completed in 2004 at a cost of $1.3 billion. As of August 2004, estimated costs had increased to $5.1 billion and completion was not anticipated until at least 2012. Numerous factors contributed to the delays and cost increases, including the increasing costs of steel and fabrication, the lack of bid competition, the selected structure type, and Caltrans’ management practices. But the signature span, although it comprises only 14 percent of the length of the bridge, is responsible for the majority of these delays and cost increases. Despite extending the bid period for the main span superstructure by 13 months in an attempt to increase competition, only one bid was received in May 2004, and it was approximately double the engineer’s estimate.32 The legislature was unable to approve a revised budget to cover increased costs, and so Caltrans was forced to allow the lone bid to expire in September. Since then, the State has been wrestling with the question of how to proceed with construction. It assembled several advisory committees to provide a technical analysis and risk assessment of the various options and to make recommendations. These options included re-bidding the selfanchored suspension span with modifications to the contract specifications; simplifying the superstructure and substituting a concrete tower for the self-anchored suspension span’s steel tower; replacing the self-anchored suspension span with one or more cable-stayed spans; and eliminating the signature span entirely and extending the skyway. As of May 2005, no decision had been made. Completing the Bridge At this stage in the construction process, redesigning the entire bridge is not a viable option. However, developing an ideal plan—a conception of what should have been—helps reveal principles of design that can guide the successful and expedient completion of the current project. The design process and resulting bridge highlight aspects of the actual process and design where there is or was room for improvement. Identifying and learning from a project’s mistakes are crucial to ensuring the success of future undertakings My personal efforts to design and engineer a span whose aesthetics, efficiency and constructability surpass those of the new bridge resulted in a continuous span across the Bay, with no Skyway, similar to the one advocated by Oakland Mayor Jerry Brown. The bridge is a lightweight, recursive cable-stayed structure with a thin steel deck and nine stiff paired towers comprised of narrow columns of reinforced concrete connected by a hollow steel box. The spans increase uniformly in length and height from east to west in response to increasing water depth and bridge elevation, allowing standardized deck, tower and cable sections to be prefabricated offsite and rapidly assembled. Such a bridge, designed using AASHTO LRFD Design Specifications and the site investigation and technical requirements used for the bridge currently under construction, performed outstandingly under static and seismic load analysis using a safety evaluation earthquake. This investigation, in conjunction with the recommendations of the Independent Review Team of bridge engineers assembled last fall at Caltrans’ request,33 leads to two conclusions: that the design chosen through an impartially judged international design competition would have been a continuous cable-stayed span; and that replacing the self-anchored suspension span with a cablestayed alternative offers the best solution to the current problem. Doing so comes closest to achieving the timeless principles that guided the design and construction of the original Bay Bridge in 1936: efficiency, ingenuity, and rational design governed by the uniquely difficult characteristics of the site.