You may have first read of the vibration conjecture concerning the Minnesota bridge collapse here, though Pat Doyle of the Minneapolis Star-Tribune quoted a former National Transportation Safety Board chairman as suggesting the possibility that vibration was potentially an important issue in a story that appeared Thursday, a day before my jackhammer physics post.
Following my post was an excellent Chicago Tribune story (see below) on the opinion of structural engineers about the plausibility of the vibration conjecture. Yet, TV news has mostly ignored that issue, as have major print media outfits, other than those that ran the Doyle story. An AP reporter also quoted one expert to that effect within a larger story, but no AP feature on that issue has shown up.
I ran a search of the words 2007, bridge, vibration (or vibrations) at the New York Times, Washington Post, London Times, Reuters and BBC and came up with zilch in every case. Likewise for searches of ABC, CBS, NBC, CNN, MSNBC and Fox News. A Google search shows little coverage.
Still, today is Sunday, so it is possible the vibration angle will appear in various newspapers. Yet, the fact that it is missing from TV news -- as if Americans can't absorb the word vibration -- suggests a general agreement to spike the story.
So why would establishment media largely shrink from covering such an obvious follow-up issue?
Paranoia is a possibility. News chiefs fear being accused of putting ideas into the heads of terrorists. What if terrorists, posing as construction workers, use jackhammers to set off a bridge collapse? The fact that for any particular bridge the possibility of success is extremely remote wouldn't enter the discussion.
Then there are those in the invisible government who are horrified at the idea that yours truly might be on the right track about a structural collapse. Does that mean -- dear God -- that there are experts who agree with this critic about the 9/11 building collapses?
Sunday, August 5, 2007
Political intimidation bill clears House
The House went along with the Senate's OK of a Bush demand for widened warrantless eavesdropping, reputedly as part of a "terrorist surveillance" program.
OK, so what terrorist in his or her right mind is going to make it easy for the NSA to eavesdrop? Don't you suppose they'll be using strong encryption -- provided by sympathizers in their region -- along with sophisticated measures such as digital pictures containing extra pixels that encode secret messages? True, it is possible to detect and just maybe decipher such messages, but the work involved certainly will slow down intelligence collection.
So then why pass such a bill? As one civil liberties activist noted, what this bill means is that there is a strong likelihood that politically active people will come under NSA surveillance.
The invisible government -- oligarchs, spook honchos, media potentates and a certain element of the hard left -- hopes to cow critics into silence. No? Recall the no-fly program. Many people who did not remotely fit the profile of a terrorist have nevertheless been barred from flying based on their political activism. Recall Bush's recent edict unilaterally authorizing the Treasury to freeze assets of anyone, including Americans, whose political activity was deemed to assist people who might be violent.
Fortunately the surveillance bill has a six-month sunset clause, but Congress nevertheless took a dangerous gamble with our liberty.
OK, so what terrorist in his or her right mind is going to make it easy for the NSA to eavesdrop? Don't you suppose they'll be using strong encryption -- provided by sympathizers in their region -- along with sophisticated measures such as digital pictures containing extra pixels that encode secret messages? True, it is possible to detect and just maybe decipher such messages, but the work involved certainly will slow down intelligence collection.
So then why pass such a bill? As one civil liberties activist noted, what this bill means is that there is a strong likelihood that politically active people will come under NSA surveillance.
The invisible government -- oligarchs, spook honchos, media potentates and a certain element of the hard left -- hopes to cow critics into silence. No? Recall the no-fly program. Many people who did not remotely fit the profile of a terrorist have nevertheless been barred from flying based on their political activism. Recall Bush's recent edict unilaterally authorizing the Treasury to freeze assets of anyone, including Americans, whose political activity was deemed to assist people who might be violent.
Fortunately the surveillance bill has a six-month sunset clause, but Congress nevertheless took a dangerous gamble with our liberty.
Saturday, August 4, 2007
Senate endorses treason
The U.S. Senate has yanked both the impeachment, treason, abuse of power, and accountability issues off the table by backing Bush's demand for an expanded warrantless eavesdropping program.
The GOP, Lieberman and 16 Democrats voted to give Bush this power, and also voted to send a signal that they agree with "the system" -- oligarchs and media potentates -- in upholding the authority of Bush and Cheney despite outrageous evidence of treason on 9/11 and repeated abuses of power. They are saying Bush and Cheney are fit to lead.
It isn't only Bush, Cheney and a group of top-level spooks who are evading accountability, as this vote shows. It is also a group of business oligarchs who don't favor their dirty laundry being aired, as it inevitably would be in a close-up on treason.
Hopefully, the House will adjourn without acting on this despicable measure, but chances are that the wire-pullers will maneuver the House into going along.
The GOP, Lieberman and 16 Democrats voted to give Bush this power, and also voted to send a signal that they agree with "the system" -- oligarchs and media potentates -- in upholding the authority of Bush and Cheney despite outrageous evidence of treason on 9/11 and repeated abuses of power. They are saying Bush and Cheney are fit to lead.
It isn't only Bush, Cheney and a group of top-level spooks who are evading accountability, as this vote shows. It is also a group of business oligarchs who don't favor their dirty laundry being aired, as it inevitably would be in a close-up on treason.
Hopefully, the House will adjourn without acting on this despicable measure, but chances are that the wire-pullers will maneuver the House into going along.
Vibration a top suspect in collapse
Construction machinery vibration is high on the list of suspects in the Minnesota bridge collapse, according to a Chicago Tribune story.
Because of the bridge design, extraordinary care was called for in I-35W's concrete repaving work, experts told the Tribune's John Hilkevitch.
"Pavement pounding can damage a bridge truss member or the floor beams; precautions must be taken," said Karl Frank, a structural engineering professor at the University of Texas at Austin.
An anonymous engineer who was on site prior to the collapse told the Tribune that there was a "lot of redecking going on and a ton of vibrations" from pavement grinders and jackhammers. "There was also a lot of equipment on the bridge -- probably more than they should have had on there."
The vibrations from the pneumatic hammers and from the 1000-pound ramming heads could cause one weakened truss to fail and set off a cascade of structural failure, experts told Hilkevitch.
The steel support structure under the roadway had shown signs of metal fatigue in a number of places, though they seemed routine and set off no alarm bells. But, small cracks can spread under persistent heavy pounding, according to Edwin Rossow, professor emeritus of civil and environmental engineering at Northwestern University.
"If that is what happened -- and it's purely speculative at this point -- the newly weakened condition of the bridge would then be exposed to the heavy rush hour traffic on one side of the bridge, affecting how loads are delivered to the superstructure," Rossow said.
Because of the bridge design, extraordinary care was called for in I-35W's concrete repaving work, experts told the Tribune's John Hilkevitch.
"Pavement pounding can damage a bridge truss member or the floor beams; precautions must be taken," said Karl Frank, a structural engineering professor at the University of Texas at Austin.
An anonymous engineer who was on site prior to the collapse told the Tribune that there was a "lot of redecking going on and a ton of vibrations" from pavement grinders and jackhammers. "There was also a lot of equipment on the bridge -- probably more than they should have had on there."
The vibrations from the pneumatic hammers and from the 1000-pound ramming heads could cause one weakened truss to fail and set off a cascade of structural failure, experts told Hilkevitch.
The steel support structure under the roadway had shown signs of metal fatigue in a number of places, though they seemed routine and set off no alarm bells. But, small cracks can spread under persistent heavy pounding, according to Edwin Rossow, professor emeritus of civil and environmental engineering at Northwestern University.
"If that is what happened -- and it's purely speculative at this point -- the newly weakened condition of the bridge would then be exposed to the heavy rush hour traffic on one side of the bridge, affecting how loads are delivered to the superstructure," Rossow said.
Friday, August 3, 2007
The physics of jackhammers and bridges
Jackhammer resonance may be a plausible suspect in the Minnesota bridge failure.
We know that the Twin Cities interstate bridge was structurally deficient but not considered highly unsafe.
The National Transportation Safety Board says it will take about a year to publish its analysis of the collapse. In the meantime, here is something reporters might want to ask experts, such as engineers and physicists: Is it plausible that, in a freak confluence of circumstances, a jackhammer set off resonance vibrations in the structure that led to a sudden critical weakening of a truss?
Slow-moving bumper-to-bumper traffic was stressing the bridge to the max. The faster traffic moves, the less the load per square foot.
However, despite substandard ratings, there had been no indication that the bridge could not support such a load.
But the combination of maximum load, substandard condition and vibrations set off by the jackhammer might well have triggered breakage of a joint or truss.
A witness told MSNBC of hearing the pneumatic hammer shortly before collapse. Construction crews were on the span doing deck repaving at the time. The construction company, which was not touching structural elements, would have had no reason not to proceed with work.
When a jackhammer is used on a ground-based roadway, it sets off minor seismic waves. But the earth is so immense and dense that the waves are rapidly dissipated. However, on a bridge, the waves first have to travel through the steel structure to reach earth.
Hence an undulating motion must occur, though in most cases one would expect the waves to dissipate harmlessly. But, in a freak choice of location, the jackhammer could set off waves that set up a near resonance with the bridge span or structural part.
Additionally, the waves travel different paths through the steel support system, meaning that it is possible that most or all might recombine at some critical point, giving a laser-like energy burst. Some waves, rather than fanning out and weakening, would travel in a near linear path, preserving their strength. And there is always the possibility that, after taking different paths, they merge in phase at full strength.
In the early 1940s the new Tacoma Narrows Bridge collapsed during moderate winds. Photos showed that the bridge span twisted at a near resonant frequency. Since then, no engineer has failed to take into account the potential for wind resonance.
But, how many would think of jackhammer resonance? A jackhammer doesn't put out a great deal of energy with respect to the potential energy of the bridge. Yet, the tool is a driver: it keeps adding energy, which could possibly result in the resonance-like focusing of wave energy at a critical stress point.
The jackhammer pumping energy into the bridge from some critical point, and at just the right frequency, is equivalent to someone pushing a child on a swing, giving a shove at regular intervals. It isn't long before the child is swinging at maximum arc and, if the pusher doesn't halt the resonance, an accident will occur.
This just in: "I would be stunned if this didn't have something to do with the construction project," said David Schulz, director of the Infrastructure Technology Institute at Northwestern University. "I think it's a major factor."
Murdoch skirts anti-trust safeguards
The fact that no concerns have been voiced by U.S. antitrust regulators over Murdoch's takeover of Dow Jones and the Wall Street Journal shows either that U.S. trust laws are flawed and need overhaul or that Justice Department enforcement is inadequate.
One consideration should be the globalization of the Murdoch media. The heft of News Corp. overseas is not unrelated to the menace of media cartelism in America, but regulators are not making that connection.
Similarly, one would think that British and Australian regulators would be concerned that the acquisition of Dow Jones poses anti-competition concerns in those countries.
We know that the Twin Cities interstate bridge was structurally deficient but not considered highly unsafe.
The National Transportation Safety Board says it will take about a year to publish its analysis of the collapse. In the meantime, here is something reporters might want to ask experts, such as engineers and physicists: Is it plausible that, in a freak confluence of circumstances, a jackhammer set off resonance vibrations in the structure that led to a sudden critical weakening of a truss?
Slow-moving bumper-to-bumper traffic was stressing the bridge to the max. The faster traffic moves, the less the load per square foot.
However, despite substandard ratings, there had been no indication that the bridge could not support such a load.
But the combination of maximum load, substandard condition and vibrations set off by the jackhammer might well have triggered breakage of a joint or truss.
A witness told MSNBC of hearing the pneumatic hammer shortly before collapse. Construction crews were on the span doing deck repaving at the time. The construction company, which was not touching structural elements, would have had no reason not to proceed with work.
When a jackhammer is used on a ground-based roadway, it sets off minor seismic waves. But the earth is so immense and dense that the waves are rapidly dissipated. However, on a bridge, the waves first have to travel through the steel structure to reach earth.
Hence an undulating motion must occur, though in most cases one would expect the waves to dissipate harmlessly. But, in a freak choice of location, the jackhammer could set off waves that set up a near resonance with the bridge span or structural part.
Additionally, the waves travel different paths through the steel support system, meaning that it is possible that most or all might recombine at some critical point, giving a laser-like energy burst. Some waves, rather than fanning out and weakening, would travel in a near linear path, preserving their strength. And there is always the possibility that, after taking different paths, they merge in phase at full strength.
In the early 1940s the new Tacoma Narrows Bridge collapsed during moderate winds. Photos showed that the bridge span twisted at a near resonant frequency. Since then, no engineer has failed to take into account the potential for wind resonance.
But, how many would think of jackhammer resonance? A jackhammer doesn't put out a great deal of energy with respect to the potential energy of the bridge. Yet, the tool is a driver: it keeps adding energy, which could possibly result in the resonance-like focusing of wave energy at a critical stress point.
The jackhammer pumping energy into the bridge from some critical point, and at just the right frequency, is equivalent to someone pushing a child on a swing, giving a shove at regular intervals. It isn't long before the child is swinging at maximum arc and, if the pusher doesn't halt the resonance, an accident will occur.
This just in: "I would be stunned if this didn't have something to do with the construction project," said David Schulz, director of the Infrastructure Technology Institute at Northwestern University. "I think it's a major factor."
Murdoch skirts anti-trust safeguards
The fact that no concerns have been voiced by U.S. antitrust regulators over Murdoch's takeover of Dow Jones and the Wall Street Journal shows either that U.S. trust laws are flawed and need overhaul or that Justice Department enforcement is inadequate.
One consideration should be the globalization of the Murdoch media. The heft of News Corp. overseas is not unrelated to the menace of media cartelism in America, but regulators are not making that connection.
Similarly, one would think that British and Australian regulators would be concerned that the acquisition of Dow Jones poses anti-competition concerns in those countries.
Thursday, August 2, 2007
Random thoughts on political polling
The Gallup poll method is reputedly tried and true, but I am wondering whether it is really the best approach. Seems needlessly complicated to me.
However, the book I looked at is a bit outdated, so perhaps Gallup's method has changed. According to the book, Gallup's presidential campaign poll is based on a questionnaire designed to screen out people who aren't likely to vote. But the extensive questionnaire could itself introduce bias -- i.e., what type of voter is likely to have time or patience for such a session?
Here's how I would design a political poll. Gather data from several previous national elections to see the percentages of people who identify themselves as Democrat, Republican and independent who vote versus those who don't.
Take a random sample of Americans (only a few thousand are needed for a population of 300 million) and ask them how they plan to vote, and perhaps one or two other questions. Then weight the sample outcomes according to the percentages who in recent history actually vote.
This method should be highly accurate (95% confidence level) because it preserves the randomness while taking account of those who express an opinion but who end up not voting.
One can use this method nationally, for the popular vote, and state by state, for the electoral college result. What about big cities, with lots of Democrats, versus suburbs and rural areas, with lots of Republicans? As long as the sample for a state is random, these differences should tend to cancel out.
New exit poll strategy
Really, I doubt the claims that the 2004 exit polls were way off base because youthful poll takers across the nation nearly all ignored the randomization requirement and buttonholed "their type" who were more likely to be Kerry supporters.
However, a way to counter such a problem would be to change the randomization procedure, perhaps interviewing fewer people. The method used in 2004 required the interviewers to approach every 10th voter exiting a polling station. Yet, a proper random sample usually doesn't need 10 percent of the specific population. Neither is it necessary to check every precinct, though this makes the average person feel that the method is better.
Just as in pre-election polling, the key is a sufficiently large (but not huge) random sample from around the state. That is, X number of precincts are chosen at random. Interviewers are sent only to those precincts. There, Y number of exiting voters are queried. Quantities X and Y are easily determined using statistical methods.
But how do we ensure that interviewers don't bias the results?
Randomly sample the interviewers and have a monitor check for interviewer selection bias. Let the monitor assign a weight to the bias. So then a specific percentage of interviewers can be expected to have an average bias (standard deviation) in favor of one or the other candidate (assuming a two-way race).
Additionally, a panel of independent statisticians could review the exit poll results, with the option of a minority dissent.
However, the book I looked at is a bit outdated, so perhaps Gallup's method has changed. According to the book, Gallup's presidential campaign poll is based on a questionnaire designed to screen out people who aren't likely to vote. But the extensive questionnaire could itself introduce bias -- i.e., what type of voter is likely to have time or patience for such a session?
Here's how I would design a political poll. Gather data from several previous national elections to see the percentages of people who identify themselves as Democrat, Republican and independent who vote versus those who don't.
Take a random sample of Americans (only a few thousand are needed for a population of 300 million) and ask them how they plan to vote, and perhaps one or two other questions. Then weight the sample outcomes according to the percentages who in recent history actually vote.
This method should be highly accurate (95% confidence level) because it preserves the randomness while taking account of those who express an opinion but who end up not voting.
One can use this method nationally, for the popular vote, and state by state, for the electoral college result. What about big cities, with lots of Democrats, versus suburbs and rural areas, with lots of Republicans? As long as the sample for a state is random, these differences should tend to cancel out.
New exit poll strategy
Really, I doubt the claims that the 2004 exit polls were way off base because youthful poll takers across the nation nearly all ignored the randomization requirement and buttonholed "their type" who were more likely to be Kerry supporters.
However, a way to counter such a problem would be to change the randomization procedure, perhaps interviewing fewer people. The method used in 2004 required the interviewers to approach every 10th voter exiting a polling station. Yet, a proper random sample usually doesn't need 10 percent of the specific population. Neither is it necessary to check every precinct, though this makes the average person feel that the method is better.
Just as in pre-election polling, the key is a sufficiently large (but not huge) random sample from around the state. That is, X number of precincts are chosen at random. Interviewers are sent only to those precincts. There, Y number of exiting voters are queried. Quantities X and Y are easily determined using statistical methods.
But how do we ensure that interviewers don't bias the results?
Randomly sample the interviewers and have a monitor check for interviewer selection bias. Let the monitor assign a weight to the bias. So then a specific percentage of interviewers can be expected to have an average bias (standard deviation) in favor of one or the other candidate (assuming a two-way race).
Additionally, a panel of independent statisticians could review the exit poll results, with the option of a minority dissent.
Wednesday, August 1, 2007
Don't cry, fight
Well, if the Ottaways and disaffected Bancrofts are really upset with Murdoch's takeover, why not compete? Or does Murdoch's takeover deal include a no-compete agreement? Even if it does, one can always find ways to silently back a competitor.
Why not gather together a group of investors, some flush with Murdoch bucks, to set up a really new media outfit, one without all the baggage of antiquated ways? Form a hybrid of the best of the new and the old media to form a concern that makes a statement: Excellence, honesty and reliability are what we sell.
I doubt whether a no-compete clause can cover a general interest concern that includes expert business coverage. In fact, one can always make a legal case that there is a key difference between business news and financial news.
Though Murdoch is planning to parlay Dow Jones into a business news network that competes with CNBC (which for the next few years has exclusive rights to Dow Jones data), there is also this: an international conspiracy to limit the presidential campaign discourse and assure an outcome acceptable to Murdoch's silent partners. Whether this ploy will work as the information age rapidly morphs is hard to say.
Anti-dictator deal needed
No one in his or her right mind should trust that Bush/Cheney won't invoke some form of martial law in order to keep control.
What is needed is a deal that if Bush lifts a pinky one more time in that direction, impeachment proceedings will begin against him and Cheney. Pelosi, who would become interim president, would need to give her word that she would not run for election to the presidency in 2008. That would placate the current Democratic presidential candidates.
Unfortunately, that assurance would immediately make her a lame duck. But, the trade-off beats the peril of dictatorship. Amid new disclosures over Bush's sweeping surveillance programs, one can hardly claim that concern over the peril of dictatorship is merely a result of a paranoid conspiracy theory.
Why not gather together a group of investors, some flush with Murdoch bucks, to set up a really new media outfit, one without all the baggage of antiquated ways? Form a hybrid of the best of the new and the old media to form a concern that makes a statement: Excellence, honesty and reliability are what we sell.
I doubt whether a no-compete clause can cover a general interest concern that includes expert business coverage. In fact, one can always make a legal case that there is a key difference between business news and financial news.
Though Murdoch is planning to parlay Dow Jones into a business news network that competes with CNBC (which for the next few years has exclusive rights to Dow Jones data), there is also this: an international conspiracy to limit the presidential campaign discourse and assure an outcome acceptable to Murdoch's silent partners. Whether this ploy will work as the information age rapidly morphs is hard to say.
Anti-dictator deal needed
No one in his or her right mind should trust that Bush/Cheney won't invoke some form of martial law in order to keep control.
What is needed is a deal that if Bush lifts a pinky one more time in that direction, impeachment proceedings will begin against him and Cheney. Pelosi, who would become interim president, would need to give her word that she would not run for election to the presidency in 2008. That would placate the current Democratic presidential candidates.
Unfortunately, that assurance would immediately make her a lame duck. But, the trade-off beats the peril of dictatorship. Amid new disclosures over Bush's sweeping surveillance programs, one can hardly claim that concern over the peril of dictatorship is merely a result of a paranoid conspiracy theory.
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