Bridges Again

The background story on the Minneapolis bridge failure is not as complex as you might think. 

The first deep understanding you must have is that Gravity Always Works. 

The second deep understanding is this:  All Machines Break.  

Engineers look at the design of a machine and figure out a reasonable safety margin to design into the machine, based on good judgement, previous experience and then adds another percentage as a "Murphy’s Law" pad.  This is true for machines as simple as crowbars, or as complicated as aircraft.

Since all machines break, the object of maintenance is to inspect and fix small failures before they become big, expensive failures.  To inspect and fix, you need to know the expected lifetime of the machine. 

A disposable lighter has a short lifetime and the inspection consists of making sure it leaves the factory in good condition.  There is no need, or procedure for field inspection and repair.  At the end of the service life (when it runs out of butane) or if something goes wrong with the flint wheel or striker parts of the machine, you throw it out and get a new one. This no-fix mode doesn’t work for bridges.

The working machine parts of a bridge are the structures that transfer the weight of the bridge (and the things on the bridge) from one place to another, while allowing passage across the bridge over a certain length.  Usually that means over an obstruction of some sort, like a river, or a valley where it would be impractical to make those on the bridge climb or descend steep gradients or get very wet.

That’s all there is to a bridge.  Some kind of structure made of stuff, designed to last a certain amount of time, to do a particular job, to safely go over some natural obstruction. 

Weave together a bunch of swamp reeds to make a rope.  Rope works as a bridge with some planks in between, to allow individuals to cross, on foot, from one side to another.  That fulfils the basic requirements.  Except rope wears out and rots, wooden planks eventually splinter and if nobody checks these things, it becomes unsafe, breaks and someone falls to their doom. 

So far, we’re not into rocket science are we?  Now it is a question of scale.  Not just size, but financial scale too.

We know that stones work, especially if we arrange them in arches so the river below can still pass.  But it’s a bugger to figure out the math of how many arches, how wide, how tall, how many workers, how long it takes to pile the rocks and how are we going to hold the rocks together. 

Then there is the problem of rocks:  They’re not consistent.  Some rocks under compression are fine, others, like slate, shatter apart and break.  Now we need someone who knows rocks as our expert and someone else who knows math and arches and someone else who can figure out where to put the strongest rocks and where we can put smaller or weaker rocks.  That starts to cost some money.  Romans figured this stuff out a few thousand years ago.  Some of their work is still up.

Abraham Darby and Thomas Pritchard figured out how to do it with cast iron in 1773 in Shropshire, UK, over the Severn River Gorge.  It was completed in 1779 and is still standing.  The first US iron box girder bridge was built in 1839 over Dunalp’s Creek in Brownsville, Pennsylvania.

Fast forward to today.  We know that steel, concrete and iron work well as parts of a bridge machine.  We know that the base for a bridge should not be on swamp, or a random pile of twigs.  Bridges are heavy things at the best of times.  We know that steel, concrete and iron will rust, weaken and degrade over time making the bridge machine less safe.  Eventually gravity, which always works, takes over and the bridge falls down.

Nothing exotic yet?  It’s simple enough to understand?  OK, just checking.

We know that if we paint and maintain the bridge every couple of years, the bridge will last a long time.  That means check the rocks, stones, nuts and bolts.  Look at the welds, scrape off the rust and patch any parts that are suspect, then the bridge will stay up and be safe for a long time. 

We also know that eventually, the bridge will be nothing but patches and paint, so we had best plan now for how to pay for a new bridge in the same place.  Are there any huge leaps of logic I’m taking here? 

Following along, the US Federal Highway Administration has studied the problem and come to the conclusion that there are 70,000 bridges that are "structurally deficient" according to their own studies, why are the bridges still open and being used?  There’s a logic gap there, that I’m not understanding very well.

Yes, it will take $188 Billion to fix all the deficient ones in the US, while the others slowly rust away and become ‘structurally deficient’ too.

But to keep some perspective, using the National Priorities Project "Cost of the Iraq War" calculator as a rough guide, Minnesota has already pumped $10.7 Billion into the Iraq war, while the total tab for the whole US is estimated at $449 Billion dollars so far.  I’ll even divide that number in half, just to take out any political hype or axe-grinding, so $224.5 Billion. 

That’s how much the US Government has dumped into enforcing a regime change and getting a nice photo of President Jo Jo The Idiot Boy in front of the "Mission Accomplished" banner on an aircraft carrier.

There is the issue of nearly 4,000 dead soldiers, but let’s leave that out of our calculations, simply because they only managed to kill 5 in Minneapolis when the bridge collapsed.  It’s cold, but we’re talking bridge fatalities, not bullet and bomb fatalities.   

Or, to put it very simply, with what the US has paid fighting in Iraq, they could have fixed all the structurally deficient’ bridges in the US and still had $36.5 Billion left over to fix some of the borderline cases. 

By the way, all that money for the Iraq War?  That’s all ‘new’ money that the US came up with out of the blue.  There was no future wars line item reserve in the US Budget in 2001, 2002 or 2003.  Unlike the various state and federal agencies who have to predict and juggle slender budget needs years in advance, the Pentagon decided they needed a couple of hundred Billion dollars, pronto. 

I wonder if someone will hang a "Mission Accomplished" banner on the wreckage of the I-35W bridge for President Jo Jo The Idiot Boy to stand in front of today when he does his tour of the site.