Transcriber: Julia Golubnichaya Reviewer: David DeRuwe
This is the Hernando de Soto Bridge that carries traffic on I-40
over the Mississippi River between Arkansas and Memphis, Tennessee.
In May of last year, a team of engineers hired to inspect the superstructure,
that’s the truss work above the roadway,
happened to notice a crack in a structural member below the deck.
This crack passed almost all the way through one of the arched eyes,
which are considered fracture-critical members.
In other words, you lose this member, you lose the entire bridge.
Recognizing the severity of the situation,
the engineers immediately called 911 and had the bridge shut down,
and it stayed shut down,
this critical link between two states,
for more than three months while repairs were completed.
It was complete luck that engineers hired to inspect
a different part of the bridge happened to notice the crack
and recognize its severity before it turned into a disaster.
And if a bridge that looks like this,
that serves as an iconic part of the landscape
and a vital link over a major river, can experience such a blatant oversight,
not to mention a violation of federal bridge safety standards,
how much confidence does that give you
in the safety of a bridge that looks like this,
something you’re much more likely to drive over in your daily commute?
Infrastructure doesn't last forever.
Most projects are designed with a lifespan of 50 to 100 years,
which means a lot of the stuff that we’ve built over the past century,
and we built a lot of stuff, is starting to show signs of its age.
The American Society of Civil Engineers estimates right now we’re spending
just around half of what’s needed to maintain a state of good repair.
And that bill is eventually going to come due.
Just the past few months,
we’ve seen a bridge collapse in Pittsburgh
and a citywide boil water notice in Austin
because of problems at the treatment plant.
What’s worse is that waiting to address these problems
until it becomes absolutely necessary, like after a major failure,
is far more costly, disruptive, and risky
than just keeping up with regular maintenance over time.
You don’t need a civil engineer to tell you an ounce of prevention
is worth a pound of cure.
Underinvestment in infrastructure’s a thing we’re somewhat familiar with.
We see headlines about it regularly.
Major federal legislation last year brought it into the spotlight
and is hopefully a big step towards turning the problem around.
Still, politicians, planners, and government officials at every level
face an uphill battle in getting the public
interested and involved in infrastructure.
It’s either too boring, too complicated, or both.
We need to understand our connection to the constructed environment,
in order to care for it and invest in it,
which means we need to know a little bit about how it works.
We grow up with all this infrastructurearound us,
taking most of it so for granted that we hardly even realize it’s there.
These elements of our environment that meet our basic needs of clean air,
fresh water, sanitation, and transportation,
they’re practically invisible to us.
They’re hidden in plain sight,
and I think that solving our problems with infrastructure
starts with just opening our eyes to the constructed environment.
Let me show you just a quick example of what I mean:
This is a picture that I took right outside my house. Anyone recognize this?
A utility pole, right? You’ve probably seen thousands of these in your lifetime.
But with a show of hands,
how many of you have ever taken a good, hard look at one of these?
Like for more than 30 seconds?
I don’t see many hands.
Keep your hands up if you can tell me what every single one of those wires does.
Not very many.
On the surface, it seems like a utility pole serving a fairly simple,
some might even say utilitarian purpose
of distributing power to homes and businesses.
But the truth is a little bit more complicated
and I think more interesting and engaging than that.
So let me tell you just a few of the things
that I see when I look at these ubiquitous objects,
and I think you’re going to walk out of the room
looking at these poles just a little bit differently.
Distributing electricity isn’t that complicated,
it all happens on wires, but if you want to move
a lot of electricity to every single home and business in an entire city,
it’s much more cost-effective to use high voltage,
like in the thousands of volts.
But high voltage is dangerous because the electricity can jump across gaps,
so we have to keep these energized lines high up off the ground
at the very top of these poles.
And electricity is normally distributed in three individual phases,
so in commercial areas you’ll see them run together like this.
And in residential areas sometimes they split the phases apart,
and so you might see one, two, or three energized lines at the top of a pole,
plus a return wire to complete the circuit we call neutral.
You can’t just set high voltage lines directly on a wooden crossbar
because wood isn’t a good insulator, especially when it gets wet,
so we use ceramic insulators to isolate the energized lines from the pole
and keep the electricity from using it as a short circuit to ground.
But if an energized line does come into contact with something on the pole,
it can create a shock hazard to people below or start a fire,
so we also include ground wires along each pole as a safety measure.
Now we have power to the pole, but it still has to reach the customers.
Every connection from the grid to a home or business is called a service drop,
but we can’t send high voltage into buildings,
again because it’s too dangerous.
So we have to take that high voltage and lower it to a lower level,
and we do that using transformers, very simple devices,
essentially two coils of wire and a can of oil.
But even though they're simple devices, transformers are expensive,
so we install fuses to protect them against surges and faults
like lightning strikes and wayward squirrels.
That’s just the electricity part.
There’s also other utilities that need to reach individual homes and businesses
like cable, telephone, and fiber optic lines.
We already have these poles, so we string them along, too, in many cases,
but we don’t want our cable and telephone technicians being shocked,
so we include a safety space below the energized lines for them to work.
And all these cables and wires create a lot of stress on a pole,
so we also include guy wires
in some cases to balance the forces and keep things upright.
I could keep going, but I’m running out of room on my diagram here
and I know this is kind of a mess, but that’s kind of the point, right,
because hopefully you’re seeing now that even the simple utility pole,
one of the most basic pieces of infrastructure out there,
is really a monument to the solutions of 100 practical engineering problems,
all of which are out there right in the open for anyone to have a look.
And noticing even just a few of these details
and understanding even just a tiny bit about how these things work
can convert the act of looking at infrastructure
from a mundane inevitability into an everyday diversion and joy.
My wife sometimes accuses me of having my head in the clouds
when I was looking at a cool piece of equipment
at the top of a utility pole or antenna tower.
When the news came out about the Hernando de Soto Bridge crack last year,
it reminded a gentleman of a kayak trip he took on the Mississippi River in 2016.
He went home, looked through his photos, and found one that included the bridge.
Sure enough, you could see the crack from the water below.
This was five years before that team of engineers
noticed a crack and sounded the alarms.
I think there’s some big lessons here for state DOTs involved in this incident,
but I think there’s a lesson here for us, too,
because even though that crack was invisible
to the roughly 100 million vehicles that passed over the bridge
during those five years, it was visible to anyone on the water below.
And not a single person had ever been curious enough
to look up where they might have noticed and reported it.
Now, I’m not saying we should all be ad hoc structural engineers
observing the conditions of every bridge we cross over,
but I do think that we all have some responsibility
for how the world gets built around us.
Investment in infrastructure
requires that we care for it and appreciate it first.
And an easy way to do that is just to look up.
Thank you.
(Applause)