Investigations into the 2007 collapse of the I-35W bridge are wrapping up and being reported. Here's an interesting report on what role the sun and its energy may have played in the timing of the bridge's collapse on that fateful Aug. 1 day. Oh, and my apologies to Elton John for swiping his lyrics for the headline of this post.
A friend of mine has a holiday visitor from Lithuania who's a highway engineer and very interested in the I-35W bridge collapse. Looking for ways for him to learn more about last summer's bridge collapse, I just found this at the official bridge building website: View the construction progress every Saturday at 11 AM for a free Sidewalk Superintendent Talk led by project representatives who will describe the design/build process and answer questions. Everyone is welcome! Meet at the corner of Washington and 19th Avenues (in front of Grandma's Saloon).
I guess this qualifies me to officially be a “wonk,” but one of the things I love to do at the Minnesota State Fair is take the issues poll at the Minnesota State House of Representatives booth at the Education Building. Fair-goers this year weighed on their opinions on a number of issues that have been recent Science Buzz topics.
First the disclaimer, this poll is by no means scientific and the results are drawn from the responses of about 7,000 fair-goers. Even worse, based on what I’ve seen from past years, lawmakers rarely take these opinions into consideration when drafting legislation on the topics.
Here are Science Buzz worthy highlights from the poll:
• Should the fine for moving traffic violations be doubled if the driver is using a cell phone at the time of the infraction?
Yes -- 66.6%
No -- 25.7%
Undecided/No Opinion -- 7.6%
• Would you be willing to pay an extra 10 cents per gallon for gas if all the money goes toward state road and bridge improvements?
Yes -- 58.3%
No -- 33.5%
Undecided/No Opinion -- 8.2%
Interestingly, last year only 41% of poll responders said yes to the same question prior to the I-35W bridge collapse.
• Do you support legislation that would prohibit people from suing food manufacturers and vendors for weight gain as a result of consuming certain foods?
Yes -- 68.6%
No -- 24.3%
Undecided/No Opinion -- 7.1%
• Should the state allow for medical uses of marijuana?
Yes -- 58.0%
No -- 30.3%
Undecided/No Opinion -- 11.7%
• Should smoking be prohibited within 50 feet of an entrance to public buildings?
Yes -- 70.2%
No -- 24.7%
Undecided/No Opinion -- 5.1%
• Should grants be made to public school districts to provide locally-grown food as part of the school lunch program?
Yes -- 61.3%
No -- 26.6%
Undecided/No Opinion -- 12.1%
• And this just for fun: Invented in Faribault in 1926, should the Tilt-A-Whirl be designated the State Amusement Ride?
Yes -- 47.3%
No -- 21.5%
Undecided/No Opinion -- 31.2%
What do you think of these public opinions? Share your thoughts here with other Science Buzz readers.
Tuesday’s Star Tribune carried a story about how problems with pigeons and spiders complicated bridge inspections over the past 13 years. How could those creatures play a part in a bridge going down? Read on.
Pigeon poop is a nuisance in all urban areas and was chronicled in this post to Science Buzz a few months ago. And evidently at the I-35W bridge, pigeon droppings were a big problem. Large numbers of pigeons were nesting in the box beam sections of the bridge structure from as far back as 1994. The box beam is vertical support beam between the bridge deck and the supporting floor beam below the bridge. The box beams had holes in them for inspectors to look inside, but that was also the access that pigeons were using to get inside and build nests.
With large numbers of pigeons in the bridge came heavy amounts of pigeon droppings. And the waste matter in those droppings can be very corrosive to metal. The solution taken in 1999 to solve that problem was to put plastic covers over the box beam holes. And those areas were some of the most critical areas for fatigue cracking that was occurring in the bridge. Some are now wondering if those plastic covers limited inspectors’ views of these critical areas of the bridge.
As for the spiders, inspectors said that the huge number of spider webs in and under the bridge could often be confused for bridge structure cracks.
The story also mentioned one other species that made inspections more challenging to engineers: humans. While the inspection work would be targeted to non-rush hour times from 9 a.m. to 3 p.m., inspectors said they still were often the targets of road rage from passing motorist who felt inconvenienced by having one lane of the bridge shut down during the inspection. Inspectors said they even had object thrown by passing drivers as they were trying to do an inspection.
Here are some of the most interesting perspectives on the 35W bridge collapse that I have run across in the last few days:
Cell phone network sends ominous signals - Engineers at T-Mobile were alerted that something had gone wrong right after the bridge collapse. They hadn't heard the new yet but saw a sharp change in cell phone activity on their network.
Government spending collapsed as well - A graph of US government spending on infrastructure over the last 55 years.
Historians and engineers have a thing or two to learn from each other - An editorial from 2006 of the history of engineering disasters.
Bridges made from glass - A prescient report from the National Science Foundation on poor infrastructure and the future of bridge technology.
"Dr. Mannur Sundaresan, professor of mechanical engineering, has developed a single channel continuous sensor that has the potential to detect and locate early crack growth in structures, thereby providing timely information to prevent catastrophic failures. This single channel continuous sensor can detect the leading edge of the acoustic emission event, occurring anywhere in the region covered by the sensor." North Carolina A&T State University
A former chairman of the National Transportation Safety Board, who just happened to be in the Twin Cities the day of the bridge collapse, raised some interesting questions. Jim Burnett was interviewed by the Star Tribune today and said that bridge collapses usually have two main causes: vibration and fatigue cracking.
Earlier inspections of the bridge have noted that it showed signs of fatigue cracking, but not to the degree that officials felt the bridge needed immediate attention. But I haven’t heard a lot of comment in press accounts, yet, about vibration. Burnett pointed out that two primary causes of vibration were going on or near the bridge at the time of the collapse: construction work on the bridge’s road deck and also vibrations from a train passing underneath it.
“Vibration is one of things that cause cracking to propagate," he said to the newspaper. "They will be looking at that."
He was on the scene of the collapse at 5 a.m. today (Aug. 2) before sharing his preliminary thoughts on the collapse. But his analysis got me thinking to the role vibrations have played in other bridge failures.
Remember the Hyatt Regency hotel walkway failures in Kansas City in 1981? About 2,000 people were there for a dance contest. The hotel featured several walkways suspended at the second, third and fourth levels over the hotel’s atrium. When people started dancing on the walkways, the vibration of the feet moving together caused them to collapse, killing 114 people and injuring more than 200 others.UPDATE: See the comments below for clarification on the Kansas Hyatt disaster.
Digging around a little more, I found these postings by engineers at the Ask a Scientist website.
Here’s some observations from engineer Vance Calder: An army troop marching at full cadence is ordered to stop marching and walk across a bridge at each soldier’s own individual gait. The "in time" stepping produces vibration, the multitude of soldiers adding to the vibration. When trying to think of waves, think of waves in water. Opposing waves can cancel each other. But like the troops moving in the same direction, the waves can add to each other and gain extra strength.
More points from engineer James Prxewoznik include: Vibration, in general, is bad for materials. It can lead to fatigue of parts and eventual failure. There are two types of vibration: free vibration and forced vibration. Free vibration occurs through actions of forces inherent with its design. Forced vibrations come from external forces outside the design of an object. If those two forces coincide, the vibration oscillations can magnify causing an object to come apart.
There might have been a lot of vibration at play on the 35W bridge: jack-hammering and other construction work, the train passing underneath, and don’t forget, it was an extremely windy day in Minneapolis on Aug. 1. A lot more needs to be checked out, of course. But investigators will likely be looking at how many different forms of vibration combined on the bridge at the time of its collapse.
Investigators are going to recover the pieces of the collapsed I-35W bridge and reassemble major sections (just like they do with crashed airplanes) to try to find a cause for the disaster. Seeing all the pieces in the proper order can help investigators figure out what went wrong and which bits failed first. The process could take a year or even longer.
According to this article in the New York Times ("Engineers see Dangers in Aging Infrastructure"), disasters like yesterday's bridge collapse may become more common if we don't find better ways to detect potential problems and invest in maintaining our aging roads, bridges, and other public works...