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Archive for January, 2012

The bridge failure stats from the previous post were updated through 2006, but I originally started looking at the stats when I was in grad school in 2000, and the data itself was no more recent than 1991.  (True story, back then 42.3% of all failures were dinosaur related.)  When I got my hands on the 2006 update I thought it might be interesting to look for changes over time.

I was looking for a change in the distribution of the failure causes.  As the statistics from the last post point out, the majority of bridge failures are caused by hydraulic issues, but hydraulic factors have always been one of the least understood parts of the bridge design process.  Through the 1980’s it was mostly an approximate process.  That all changed due to two major bridge failures, one in New York state and one in Tennessee.  Lives were lost during both failures, and both drew a lot of attention nationally from the public and from engineers.  As a result, a lot of research has been done on bridge hydraulics and scour and state DOTs developed design standards in these areas.  So I was curious to see if that shifted the failure statistics away from hydraulics.

Nope.  Sure didn’t.  The statistics from the 2006 dataset were surprisingly consistent with the 1991 data.  Hydraulic failures went from 60% to 58% with the 2% drop being offset with a 2% rise in overload failures.  Since the 2006 data was merely an updated version of the 1991 data I decided to separate it into pre 1991 and post 1991 data sets.

So as one final check of the data, I separated the New York state data from the rest of the country.  The assumption being the New York data would be more comprehensive since New York State DOT was collecting the data.  The resulting analysis did show a significant shift.  Hydraulic failures dropped to 48% while collision failures went up to 26%.  I think this is because collision failures happen more often on smaller bridges and aren’t as widely reported in the national media.

I don’t think it’s a good idea to make any grand conclusions due to the nature of the data collection, but I suspect the analysis of the New York state failures shows the distribution between hydraulic and collission failure causes more accurately.  The most surprising part of the analysis was how consistent all the numbers were.  There was very little change from 1991 to 2006, and even breaking out just one state showed almost no change in any of the failure causes other than hydraulic and collision.  (And earthquake failures were not represented in the New York data.

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Over the weekend the local news stations were carrying a story about a bridge failure in Kentucky.  In light of that story, it seems like a good time to share some research I’ve been doing into bridge failure statistics.

It’s tough to find any statistics on bridge failures.  Surprisingly, there’s no national database on bridge failures.  The best I was able to find is an database that New York State DOT keeps on bridge failures.  It basically includes entries for whatever they have heard about either in the media or what was volunteered by other state DOTs.  It’s nowhere near comprehensive on the national level, but presumably it would be pretty accurate for New York since they would be well informed about their own state.

Before I share the statistics, there are a couple of things to keep in mind:

  1. This includes all bridges, not just the big ones that end up in the national media.  Most bridges are small structures  and not of interest to anyone outside the immediate area they are located in.
  2. Failure doesn’t necessarily mean going down in a spectacular cloud of dust.  A structure failure is anything that keeps it from being used in the way it was intended.  And now for the statistics…….

The biggest number of failures by far are caused by bridge hydraulics.  This means anything related to water and includes things like bridge scour, being clogged by ice or debris, approach road wash-outs, and just being pushed over by water.  Hydraulics is my specialty area and I’ll cover some of those in more depth in later posts.  The second greatest is collision.  I’m not entirely clear about this label, but I assume it means collisions by boats as well as collisions by trucks.  The overload and earthquake labels seem self-explanatory.  I assume fire refers to wooden bridges, but I do know of at least once instance  where a tanker truck blew up under an interstate bridge and melted the beams so badly the entire structure had to be replaced.  (It does occasionally happen outside of Michael Bey movies.)

I’m going to do a more in-depth analysis of the statistics in my next post so you folks who got your fill here can skip it.

 

Source: Wikipedia

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This satellite photo was taken four days after the  capsizing of the cruise ship Costa Concordia on January 13 off the island of Giglio in Italy.  To give you an idea of scale, the ship is 1000 ft long and 116 ft wide.  I assume the white line visible between the ship and the coast is a containment boom placed to keep leaking fuel from washing up on shore and will probably surround the entire ship soon.   Experts estimate it will take 7-10 months to remove the wreck.   Local residents are concerned because tourism is a big deal on the island, but they’re getting a surge of people from mainland Italy coming over to see the wreck for themselves so perhaps it will equal out.

The image is provided by Digital Globe. (click image for bigger view)

I also found this approximate representation of the ship and sea bottom.

Source: Wikipedia

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Note: All images below are by Leonardo Da Vinci.

One of my old college professors once told us a story about the difference between scientists and engineers.  You put them both in a closed room together.  The door isn’t locked, and they can take as many steps as they want.  The catch, each step can only be half the distance to the door.  The scientist would starve to death because he can never get closer than half the distance to the door.  The engineer, on the other hand, takes his ‘half way’ steps until he gets close enough.  Then he says ‘Close enough’, grabs the door know, and goes down the street to get a few beers. 

The story isn’t as funny now as it was back when I was in school.  In the real world (as opposed to a college campus) the line between engineering and science is blurry.  A good practitioner of either has to dabble in the other.  But it does strike at the heart of the difference between a scientist and an engineer.  Science is about exploring the principles that make the universe work, and it helps to be very literal down to the smallest detail.  Engineering is about taking those scientific principles and making them work to our advantage and sometimes requires a hard-nosed practicality to make things work.

In short, engineering is problem solving through applied science.  Engineering is a broad field with lots of branches , and each of those branches even further.  I’m not really qualified to talk about most types of engineering, but I do want to explore my particular branch of the engineering tree in my next post.

For a little more info, see the National Society of Professional Engineers.

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Water towr in Estherwood, Louisiana courtesy of Flickr user Bill Herndon

This post builds on the previous one about hydrostatic pressure.  If you haven’t read it yet, why not?

To me, water towers are an iconic symbol of small towns.  I’m not sure why I associate them with small towns, they’re common in larger cities also.  It must have something to do with all the small towns I visited in my younger years and my childhood fascination with big things.  My dad used to get annoyed if the shorties in the back seat asked too many questions so water towers were a good way to keep track of where we were.  They were always tarted up with the local high school mascot  and town.  Advertising uses aside, water towers have a major role in making sure everyone has enough to drink.

Of all the things that enable modern civilization, drinkable water is one of the most important.  Modern, reliable water delivery systems are what enable people to live close together and form towns and cities.  It’s something few people consider, but it’s a minor marvel that water can travel in underground pipes and somehow flow up into your house and out your faucets.  The answer, of course, is pressurization.

Every water utility of any size uses electric pumps to pressurize their distribution system, but supplying enough pressure can be tricky.  Every time someone turns on the water, that faucet acts like a leak just like letting the air out of a balloon a little at a time.  One or two leaks is no big deal, but when lots of people start using water all at once the balloon can’t blow up fast enough and people don’t get their water.  This mostly happens during certain times of the day when lots of people are using water at the same time.  This is a common problem first thing in the morning when people are showering before work, and in the early evening when everyone is fixing dinner and washing dishes, or for people who live near factories which use a lot of water.

Idealized with morning and evening peaks. Found here.

The dilemma is between the level of service to your customers and cost effectiveness.  If you buy your pumps for high demand you end up with a lot of expensive pumping capacity that sits idle 20 hours of the day.  If you pick your pumps for average demand then you save money, but it might be tough for people to get all the water they need at certain times of the day.  And we haven’t even considered the high pressure needed for fighting fires or the pumps dependency on electricity.  The system doesn’t need high volume often, but when it does need it, it REALLY needs it.

The answer to this dilemma….. the common, garden variety water tower.  Water towers are storage which sits idle until demand is higher than pump capacity.  The tower is connected to the water distribution system and gravity feeds water in as necessary.  It’s a very elegant solution as gravity pulls in as much or as little water as you need for free.  Typically the water level starts high and slowly lowers throughout the day.  Then a small dedicated pump fills the tower back up during the wee hours when most of the world is asleep and not using water.

The water tower adds a lot of flexibility to a water distribution system.  They are able to pick up the slack if one of your pumps needs to be turned off for maintenance, or if you lose electricity to a pump station.  And due to the way hydrostatic pressure works, you can create higher water pressure by building your tower higher without requiring more volume.  If you find a hill 50 ft higher than the surrounding countryside then build a tower on 50 ft legs and make it 30 ft deep you’re adding 50+50+30 = 130 ft of pressure to your system.

River to treatment to water tower to customer.

If you’re lucky, you can take advantage of existing features to build your water tower.  If you have a sufficiently hilly area you don’t even need the tower.  In 1889 Nashville built a large reservoir on a hill overlooking 8th Avenue.  New York City has taken advantage of its many tall buildings by putting water tanks on top of many of them.  Most really tall buildings provide water and pressure to their higher floors by building a water tank (or tanks) into their floor plans near the top.  This way they can provide everyone in the building water without depriving neighboring buildings.

Water towers are key features to a smoothly functioning water system and provide extra water storage and pressure in most municipal systems.  They were an important part of making sure Nashville had plenty of water when the May 2009 flood knocked out one of the water treatment plants and cut the water entering the system in half.

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I’ll admit up front, I have a celebrity crush on Kate Beckinsale going all the way back to the vintage costumes Pearl Harbor dressed her in.  So this review of her latest movie may be a little biased.  Biased, but, as you can see below, only a little.

First let’s get the recap out of the way.  Underworld: Awakening is the fourth in the franchise about the thousand year feud between vampires and werewolves (known as lycans).  Beckinsale is Selene, a vampire soldier (called death dealers for maximum bad ass) devoted to wiping out the lycans.  The predecessors in the franchise follow Selene as she discovers a conspiracy between the vampire and lycan leaders and falls in love with a hybrid man who is both vampire and lycan.  When Awakening begins we find out the vampires and lycans have a new mutual enemy.  It seems all us plain old normal humans have found out about all these secret goings-on and have decided to just kill everybody whether they’re vampire or lycan.  (But now that you’ve read it, forget about the humans.)  In the opening scene Selene is caught and cryogenically frozen in a lab.  She wakes up twelve years later and wreaks a little carnage on the poor guys in white coats.  In the ensuing carnage Selene learns that she now has a hybrid daughter whom the lycans are trying to use for all sorts of nefarious purposes.

 I ran across this quote from the Village Voice  which sums it up:  

 The entire production is single-mindedly, earnestly devoted to serving up feats of BADASS, and it succeeds in this devotion to the exclusion of everything else.

Awakenings is essentially a series of action scenes strung together continuously.  Each and every one features Beckinsale kicking ass and chopping up lycan.  If you go into it expecting nothing more than an entertaining action flick with lots of explosions and gunfire you’ll probably be okay.  There are bits of plot and dialogue between the action scenes, but I recommend you not pay too much attention to those.  If you try and reconcile the plot holes you’re just going to end up walking out of the theater with a headache.  In a particularly serious head scratcher, the first 15 minutes of the film showing human storm troopers killing vampires and lycan indiscriminately was never followed up.  Exploring that would have made for a much more entertaining movie.

My biggest complaint was actually that I had to watch it in 3D.  My local theater had two showings of the 2D version, one was too early and one was too late so I had to shell out for the 3D glasses and that was an expense I could have done without in this case.  The bullets whizzing over my head didn’t bother me, and the 3D depiction of fog and various gaseous clouds was a nice visual effect but obvious CGI.  I just begrudge having to see it 3D because the movie wasn’t worth the added expense.  If I’d been able to see it at 2D prices I probably would have been a happy camper.

 While Underworld: Awakening isn’t a good movie or even average, it isn’t necessarily a bad movie either.  The key to enjoying it is having the proper expectations (and seeing it in 2D, I really feel for the poor suckers who shelled out for 3D AND Imax).  If you’re a fan of the non-sparkly vampire genre, and you go into it without high expectations, you can probably enjoy it.  Just don’t expect a lot of plot or deep characters.

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When I was a kid I was always challenging myself to swim to the bottom of the pool.  (This was when pools were deeper than 5 feet.)  The eight foot deep pool at my neighbor’s house was easily conquered, but the twenty footer at the country club was quite a challenge (especially since we weren’t actually members at the club).  When I finally got all the way down to tag the bottom (staying clear of the drain thanks to a random episode of Baywatch) I noticed a little pain in my ears.  Twenty feet of water was pushing down on me and my ears were feeling the pressure.

The technical term for what I was feeling is hydrostatic pressure.  As dictionary.com explains it:

The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity.

Crude, but hopefully it illustrates the point

In layman’s terms… it’s the weight of a fluid (usually water) pressing down.  Hydrostatic pressure is the reason it’s so difficult to recover shipwrecks and why we can’t make it to the deep ocean bottom.

It may sound like scientific jargon, but a practical understanding of hydrostatic pressure can be useful.  For instance, an above ground swimming pool would have a drain at its bottom.  Take a hose and attach it to the pool drain turned so the water shoots up.  Instant fountain.  And the height of the water fountain is the same as the depth of the water in the pool thanks to hydrostatic pressure.  As the depth in the pool starts to go down the fountain would also get shorter and shorter.

The most important thing though…. hydrostatic pressure is dependent on the depth of the water, not the volume.  So the fountain would be just as high whether it was caused by a 30 ft pool, or a 2 ft barrel.  This is why rain barrels are useful.

Now that we’ve got this far, I can explain how hydrostatic pressure makes your ears pop when you travel to higher elevations.  The principle of hydrostatic pressure applies to air just like it does to water.   We live at the bottom of a seven mile deep atmosphere which causes a significant hydrostatic pressure on our bodies.  This is called ‘standard pressure’ or ‘one atmosphere, and is equivalent to about 33 ft of water.  When you drive up into the mountains you suddenly are experiencing a lower hydrostatic pressure, while your ears still have the higher pressure internally.  The popping is part of the mechanism for adjusting the pressure inside your ear to be the same as the outside pressure.  For the anatomical explanation, try this.

Hydrostatic pressure makes beer bongs possible, and is key to water filtration in all kinds of ways.  Next time I’m going to explain how hydrostatic pressure makes sure water comes out of your faucets on demand.

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