Questions about the West Seattle Bridge failure we should be asking; An independent forensic engineering study is necessary
By Patrick Robinson
When a vital transportation artery like the West Seattle Bridge fails, you would think that the most vital question to be answered would be why?
And the why of that leads to accountability.
We are living in a time when our leaders are increasingly being held accountable.
The same should be true of those whose duties include looking after our infrastructure.
So far what we’ve gotten from the Seattle Department of Transportation (SDOT) regarding matters following the closure of the bridge is some honestly very responsive and thoughtful action. They’ve taken many measures to address traffic mitigation and assembled a proposal that takes the views of various neighborhoods seriously. They’ve put together an emergency plan in the event of sudden failure of the bridge. They’ve installed a large number of sensors on the bridge and asked their consultants to help them review the data. They’ve created a short term repair plan to address the immediate (and possibly longer term) stability of the span and put that plan into motion. They’ve put together with the Mayor’s office a Citizen’s Task Force and a Technical Advisory Panel on a solution going forward. All necessary and commendable steps. Their Reconnect West Seattle survey effort hopes to help people reconsider their mobility choices and relieve pressure on a strained system. All of these steps are laudable and the outreach to those affected is noteworthy.
But hold on a minute.
There’s something missing. The West Seattle community, the Vashon Island community, the Kitsap peninsula communities all depended on that bridge. This is obviously a regional matter with implications for nearly everyone within 100 miles.
It was designed to last 75 years.
It lasted 36 (or technically less since the cracks were first discovered seven years ago). Thats 39 years they didn’t get.
Who is accountable here?
The failure will end up costing hundreds of millions of dollars all BEFORE we end up paying for a replacement. Real estate values declining, lost business, lost time, all over what will likely be another six years or more. If we end up requiring a toll to pay for it, most of that is likely to fall on local people.
If you believe “It doesn’t matter who’s at fault” you would be wrong.
Of course it matters.
SDOT has thus far said a mix of things may be involved. From the Nisqually earthquake (which moved the bridge 3 inches), to concrete “creep” a kind of shrinkage that naturally occurs, to the failure of the bearing at Pier 18 which limited the ability of the bridge to flex.
But the bridge was designed to be six lanes. Eight years ago SDOT and Metro added a seventh lane for transit and the fully loaded C Line buses and other transit to use. Chris Arkills from Metro said, “Service began on the C Line on September 29, 2012. The C Line replaced the Route 54, 54X, and non-commute peak trips on the Route 55, all of which already ran frequently and had increased in trips prior to the implementation of the C Line. West Seattle service was restructured at that time and some routes like the Route 22 no longer went downtown. So, while the number of buses coming over the bridge has gradually increased over the past decade due to demand and viaduct mitigation, there was not a sudden increase in the number of buses at any time.”
About the weight Arkills explained, “A fully-loaded RapidRide bus or another articulated buses in our fleet weigh between 28.6 to 28.85 tons… The bus weights did not change measurably with the implementation of the C Line, and the addition of the bus lane meant that our buses had less dwell time on the bridge and the weight was more evenly distributed. Even before the implementation of the bus lane, Metro buses were always operating in either the SR 99 on ramp lane or the one just to the left. So the actual placement of where are buses sat on the bridge is likely only a matter of feet and they probably spend less time in the far right 99 lane. The bus lane is not packed with buses, but rather has a bus passing over it intermittently.”
Still there were 387 bus trips a day. Cars have gone up in weight by an average of 900 pounds each since 1984 and traffic jams on the bridge were a daily occurrence.
The earthquake was in 2001, the bus lane was 2012. How is it that only 1 year later the cracks were first noted?
In the 2014 Bridge Inspection report SDOT noted that the bearing at Pier 18 was extruded but only said that it needed further observation. When did they notice it had failed completely? Was that in 2020?
Is this a design flaw? Or was the engineering decision to allow heavier vehicles on the bridge in an extra lane ill considered? Were engineering studies done to look at the load rating for the bridge that confirmed it could take that kind of weight? Was this a construction flaw? During construction an entire section had to be removed since too much fly ash had been added to the concrete mix and it would have resulted in catastrophic failure.
In the case of other high profile building and structure failures around the nation, getting to the root cause has been deemed an important mission.
The author of Why Buildings Fail, Ken Carper Professor Emeritus, Washington State University, Past National Chair of ASCE Forensic Engineering Division
Chief Editor Emeritus, ASCE Journal of Performance of Constructed Facilities said that understanding why structures fail is as important as understanding why they succeed.
“The investigation of constructed facilities that have not met performance expectations is vital to successful design, construction, and maintenance of future constructed works. Forensic engineering can bring about improvements in engineering design in much the same way as medical pathology has contributed to advances in the practice of medicine. But in order for the lessons to be learned, the investigations must be accurate and thorough, and the results must be disseminated openly to the relevant professionals. Most failures, particularly in facilities that have been in use for many years, result from multiple causes involving errors in design, construction, material deficiencies, and/or maintenance. A thorough investigation may provide lessons for all parties. The opportunities for learning these lessons should not be overlooked. The study of failed projects nearly always provides more useful lessons than does the study of successful ones.”
``Fear is one of the most effective emotions in the creative process,″ he said in an interview according to the Associated Press. Carper explained that people are reluctant to talk about their errors, with builders sometimes facing the threat of huge lawsuits.
Included in Carper’s book are the 1981 collapse of a Hyatt Regency Hotel skywalk in Kansas City in which 114 people were killed, the sinking of the Lacy V. Murrow Floating Bridge outside Seattle in 1990 and widespread building failures caused by earthquakes in San Francisco in 1989 and Los Angeles in 1994.
Most importantly though again, who or what is accountable here? Is this all just an act of God?
In the Journal of Constructed Facilities Volume 17 - Issue 3 of 2003 Kumalasari Wardhana and Fabian Hadipriano, P.E. F. ASCE note that “Over 500 failures of bridge structures in the United States between 1989 and 2000 were studied. The age of the failed bridges ranged from 1 year (during construction) to 157 years, with an average of 52.5 years. The most frequent causes of bridge failures were attributed to floods and collisions. Flood and scour, with the major flood disaster in 1993, contributed to the frequency peak of bridge failures (almost 53% of all failures). Bridge overload and lateral impact forces from trucks, barges/ships, and trains constitute 20% of the total bridge failures.”
The West Seattle Bridge is another example of What Barry LePatner, author of Too Big to Fall - America’s Failing Infrastructure and the Way Forward (2010) says is a $2.2 trillion repair bill across the nation. How did it get this way? Author of of Seattle City Council Insights Kevin Schofield noted that SDOT has been chronically underfunded for years. The maintenance budget is short some $75 million. He points out that “As of the end of 2018 SDOT had a backlog of 876 maintenance and repair items,” careful to mention that maintenance was not thought to be the primary cause of the West Seattle Bridge failure. Larry Summers the Harvard economics professor and former Secretary of the Treasury, said in a Hutchins Center conference “The case for spending more on infrastructure is overwhelming.”
All of which suggests that the federal government should get involved in the cost of the replacement, even though we are talking about “City Bridge.” In the the SDOT Request for Qualifications which closed on July 9 they even state that they anticipate at leas some federal funding participation.
It’s also worth noting that to build the very same style existing bridge today would cost in excess of $480 million. The cost was $160 million in 1980 dollars. That's just the cost of inflation alone. That bridge was built to a 50 year earthquake standard (odd since it was supposed to last 75 years). But any new structure will need to meet a 2500 year standard, or a 9.0 quake. The southern tip of Harbor Island happens to be where the Seattle Fault passes through.
But we need to know who the engineers were whose calculations did not allow for potential problems.
When will we see a timeline on establishing the actual cause of the failure? What is the status of that investigation? Who is independent enough to do an audit of the engineering reports and provide answers?
In late April Councilmember Alex Pederson (District 4) called for an audit to assess the conditions and maintenance of the 124 bridges Seattle owns.
They manage 317 bridges with an average age of 60 years. We need to do far more careful evaluation of how we fund and maintain our infrastructure projects, but first we need to know a lot more about how the bridge failed. We need a forensic engineering study of the bridge failure and some clear answers. As the repairs are being effected some key parts of evidence of what caused the failure could be changed or lost. Forensic engineering is the application of engineering principles to the investigation of failures or other performance problems. Should we be leaving this kind of study up to SDOT?
So far, SDOT, the Seattle City Council (aside from Alex Pederson) and the Mayor’s office have all been very quiet on the subject.
A well written assessment, however I would argue that the efforts of SDOT have been adequate, not laudable. What we're dealing with is not something new - it's 7 years in the making, right from the first observance of the cracks. THIS is when assessment and planning should have begun, not 7 years later when happenstance led them to close the bridge the very same day they may the announcement it was to be closed. The sensors that were installed to monitor the development of the cracks should have been installed a long time ago, not after the structure was deemed to be at risk and unsafe.
It would be easy to blame previous work and SDOT staff, however that work is not done in a vacuum - documentation exists. Institutional knowledge exists. This is an instance of people leaving the work to be done for someone else and the people of West Seattle deserve better.
As someone who has worked in and with the government for 20 years, your assessment could not be more wrong. How you don't see the utter incompetence of the Mayor, City Council, and SDOT, makes the voice of an elder statesmen, useless.
very good article and I agree with most of the prior comment. If Seattle doesn't require a independent investigation our federal govt should before they hand over any money on something that could fail again
For nearly 20 years, my industry (Advanced Condition Assessment Technologies) has been encouraging bridge owners to use proven, commercial technologies to objectively assess bridge condition when and as warranted, instead of relying solely on an overtly subjective process - visual inspection - to inform crucial, expensive decisions for repair or replacement. Few owners have heeded our pleas to the detriment of users and taxpayers. More precise and objective knowledge of bridge condition supports more informed decision making in terms of repair or replacement. Just because a bridge is 50+ years old doesn't necessarily mean it's safe operating life is over. However, in situations where, safety is the primary concern, these technologies should be promptly employed to ensure user safety. When the first signs of serious structural distress appeared via visual inspection (concrete cracks) the SDOT should have implemented a structural monitoring program using sensors to inform bridge engineers about crack changes over time, allowing them to assess deteriorating condition in near real time. Having such a system in place now is worthwhile, but deploying it in 2020 is years too late. Bottom line: it's time for bridge owners to step up their use of these proven technologies to both enhance user safety and to support more informed asset management decisions. Users and taxpayers deserve no less.
I would hardly say that SDOT has taken "many measures" to address traffic mitigation. The survey, which I filled out, mainly served to shame those of us who have daily vehicle needs for work (and/or are small business owners without access to resources like a shuttle, which I also am) by offering only ridesharing and public commute interventions.
Have we discussed this enough ? I vote more words, pretty please!
the west Seattle bridge was hit on the side rails by drivers over the years. One of them ping ponged back and forth until the car was smashed up ready for the junkyard. The bridge took alot of hits
It was a poor design, poor management, and now a poor failure analysis. Bridges should be build with a 500 year expected life span. When you cut corners and cut costs, you save money in the short term, but spend more later. Sad. Let the next generation pay for this mess.