Dr. Abolhassan Astaneh, U.C. professor of structural engineering, analyzed the existing east span immediately following the Loma Prieta earthquake. He has global experience and expertise in the seismic behavior of bridges and other large structures. Professor Astaneh urged officials not to approve the proposed viaduct with an asymmetrical self-anchored suspension span, after his independent analysis revealed conceptual flaws which could result in catastrophic failure of the proposed bridge.
Immediately following is the text of Dr. Astaneh’s most recent letter to the MTC Bay Bridge Task Force, followed by his original letter of last year.
Abolhassan Astaneh-Asl*, Ph.D., P.E.
Professor of Structural Engineering, University of California, Berkeley
astaneh@ce.berkeley.edu
To: Mary King (Chair), and Members of Bay Bridge Design Task Force
Date: February 24, 1999
Subject: Grave Concerns on Seismic Safety of the New East Bay Bridge Design
The Honorable Chair and Members of the Task Force;
At your meeting last year, and prior to approving the new design, I expressed my concerns about seismic safety (or lack thereof) of the new design. Since then, I have done more studies and I am now of the opinion that the new design has several fundamental seismic flaws that can result in very serious damage and possible partial or full collapse in the event of a major earthquake. In my opinion, the new East Spans if built will be seismically more vulnerable than the existing East Bay spans after minimal retrofit.
I would like to remind you that the structural system used in this bridge, the so-called "self-anchored single-tower suspension bridge" has not been used in any bridge anywhere in the world. This is not because this is a new innovative system as the designers have led you to believe, but, in my opinion and in the opinion of many prominent bridge engineers, who are independent of Caltrans and the design team, it is because the system is inherently unstable and there is no actual test data on its performance in seismic or even non-seismic environments. Even the scarce information released by the design team indicates that the tower (and there is only one!) will permanently bend 6 feet after their design earthquake and there will be serious damage to tower and other critical elements.
This bridge, which you are charged with overseeing its design, is the most important bridge in California and perhaps the U.S. Yet, it is located between two very active faults. At any given time on the average, there are 5000 people on it. If you are truly concerned with seismic safety of the people who will cross this bridge for perhaps the next 150 years, you would pause and have this design reviewed by a truly independent panel of experts in seismic design of long-span bridges. Not doing so will put the responsibility of the injuries and loss of life that may occur at this bridge on your shoulder. Please notice that unlike architectural aspects, seismic safety of structures is not in the eyes of the beholder. It is a universal science and technology that can be verified by any qualified and independent team.
The rational approach, in my opinion, to provide seismic safety, would be to hire bridge engineering firms who designed seismic retrofit of all other major bridges in California and have them design a rational seismic retrofit for the existing East Bay Spans as they have done for all other major bridges. This can be done in a span of a few months. Then, implement the retrofit immediately to make sure that there will be no major injuries or loss of life if the earthquake happens.
In the estimate of prominent engineers and contractors such retrofit should not cost more than $300M. Please notice that seismic retrofit of all other five major bridges in the Bay Area combined will cost less than $900M that Caltrans indicates will cost to retrofit the existing Easter Spans.
This retrofit should have been done over the last 10 years. After the existing bridge is fixed so we don't get killed on it, then a panel of bridge engineers who have expertise in seismic design, transportation planning, railroad lanes, and other engineering aspects can be assembled to develop a rational plan on what are the needs of a new bridge at this location. Then, a true competition can be held, without permitting the review panel members to submit and select their own designs, as was done for this new design, to select a bridge with the best seismic performance and transportation functionality as well as a pleasing architecture.
I plead with you and our Honorable Governor Davis, who is ultimately responsible for our seismic safety on this bridge; please do not ignore the concerns expressed here as you have done so far since last year's meeting. These concerns now have been expressed by many other bridge seismic design experts outside the design team and MTC, even by members of your Engineering Design Advisory Panel who are independent of Caltrans and MTC.
I will attend your February 24, 1999 meeting and will be happy to answer any questions that you might have.
Sincerely yours,
Abolhassan Astaneh-Asl
cc: The Honorable Governor Davis; The Honorable Senators Feinstein and Boxer; The Honorable Mayors of the Bay Area; Director Medina, Caltrans; Attendees of 2/24/99 Joint meeting of MTC Bay Bridge Task Force/EDAP.
To: Mary King (Chair), Sharon Brown, Mark DeSaulnier, Elihu Harris, Tom Hsieh, Jon Rubin, Angelo Siracusa (Bay Bridge Design Task Force)
Date: June 20, 1998
Subject: Concerns on Seismic Safety of the New East Bay Bridge Design
The Chair and Members of the Task Force:
I have just completed an independent and careful study of the seismic safety of the "self-anchored" suspension bridge, the design that you are currently considering for replacement of the East Span of the Bay Bridge. Several major items about seismic safety of the proposed bridge gravely concern me. I am convinced that if the proposed self-anchored bridge is constructed and the Hayward Fault ruptures, there is a high probability that the resulting earthquake can severely damage this bridge and possibly cause partial or catastrophic failure of the main span (during construction and/or after completion). Even the design report: "30% Selection Report, May 98" prepared by the design team for Caltrans indicates that there will be structural damage to the main tower and possibly a permanent bend in the tower. Also, the design report raises the possibility of various failures under or around the foundations of the main tower, which is supported on the steep slopes of the fractured Yerba Buena Island.
The SFOBB is perhaps the most important bridge in the U.S. with more than 285,000 cars crossing it daily. It is, however, located between two major active faults. Given the fact that we know little about what kind of earthquakes can hit this bridge in the future, the damage it would sustain could be far more serious than anticipated. In my opinion, there is no rationale in spending $1.5 billion to build a bridge of this importance using a highly questionable system that will very likely be unstable during a major seismic event.
Unlike regular suspension bridges, where main cables are connected to very large concrete anchor blocks, which are firmly embedded in the solid ground, in the proposed "self-anchored" suspension bride, there are no anchor blocks. The main cables are connected to the deck of the bridge. There are no major bridges built using this system and there is no experience and data on seismic performance of such a system. In the literature, there is almost no information about this so-called self-anchored suspension bridge system. Only Niels J. Gimsing, one of the most prominent bridge engineers of the world and Professor at Technical University of Denmark, has a short paragraph on self-anchored suspension bridges in his book Cable Supported Bridges. He considers this system inferior to other bridge systems.
In addition to the possible overall instability of the proposed bridge, I am also concerned about the following:
Supporting the main towers on piles instead of firm rock,
connection of main span to skyway (which in current design may not survive large earthquakes and may result in collapse of the span)
the performance of two decks separated from each other by more than 50 feet
the joints connecting the main span to the rest of the bridge.
If at any of these weak points, the performance is not as the designers assumed, partial collapse can occur.
Knowing your commitment to public seismic safety, I hope you will give serious consideration to the issues raised. I plead with you to discuss the seismic safety of the existing East Bay spans at your next meeting. As you may know, Caltrans is spending more than $50 million to strengthen the existing East Bay structure. This prudent move on the part of Caltrans can ensure that if during the next 5-6 years a major earthquake occurs, people will not get killed or seriously injured on the existing East Bay spans. In addition, in seeing how fast Caltrans rebuilt the collapsed freeways in Los Angeles after the Northridge earthquake, it should be possible for Caltrans to expedite strengthening of the East Bay span and make it safe by this Christmas. Having done that, your task force has fulfilled its responsibility for seismic safety.
After the existing bridge is made safe, the current panic and rush to get a new bridge—any bridge, safe or unsafe—will subside. Without the prevailing anxiety, a proper process (perhaps including an open international competition) would lead to a selection of a seismically safe and aesthetically pleasing bridge designed to serve the people of the Bay Area for the next century and beyond.
Sincerely yours,
[signed] Abolhassan Astaneh-Asl
cc:
The Honorable Governor Wilson; The Honorable Mayor of San Francisco, Willie Brown; The Honorable Mayor of Berkeley, Shirley Dean; The Honorable Mayor of Emeryville, Ken Bukowski; The Honorable Mayor of Oakland, Elihu Harris; The Honorable Mayor-elect of Oakland, Jerry Brown; The Honorable Mayor of Alameda, Ralph Appezzatto; The Honorable Mayor of Albany, Bruce Mast; The Honorable Mayor of Richmond, Rosemary Corbin; The Honorable Mayor of El Cerrito, Jane Bartke; The Honorable Mayor of Piedmont, Patty White; The Honorable Mayor of San Leandro, Ellen Corbett; [Mr.] Van Loben Sels, Director, Caltrans.
* A. Astaneh-Asl is a professor of structural engineering at the University of California, Berkeley. His area of specialty is seismic behavior and design of buildings and bridges. Since the 1989 Loma Prieta earthquake he has been heavily involved in seismic studies and research as well as seismic design and retrofit of major bridges in California, Japan, New Zealand and Thailand. He has conducted several studies and testing of the East Spans of the Bay Bridge and the Golden Gate Bridge. He has been on the seismic retrofit design team of the Carquinez bridges and was a seismic advisor to retrofit design of Hayward San Mateo and Richmond San Rafael bridges.
The opinions expressed here are solely those of the author and do not necessarily reflect the views of the University of California or agencies and individuals whose names appear here.
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