If you had to have a bridge collapse, it was just about the best collapse President Biden could ask for.  Nobody was killed, but enough people were injured to garner headlines.  And it happened about four miles away from where the President was scheduled to speak in Pittsburgh, Pennsylvania later the same day, Friday January 28. 

I’m sure the bus riders, motorists, and joggers who were involved didn’t think it was funny to see the Forbes Avenue bridge over Frick Park resolve itself into several large disjointed chunks.  An articulated bus slid backwards into the rubble, necessitating a rescue of the bus riders by first responders.

But later in the day, President Biden made the collapse site the first item on his tour of the city, reiterating that the $1 trillion federal infrastructure bill passed last November has money to pay for replacing old bridges such as the Forbes Avenue structure, which was reportedly two years beyond its 50-year design life when it collapsed.

Deteriorating

For years now, the American Society of Civil Engineers has displayed on their website a report card on the nation’s infrastructure, and I don’t recall ever seeing a grade higher than C.  They estimate it would take some $125 billion to completely clear the backlog of aging and deficient bridges that the nation has accumulated since its road-building frenzy of the mid-20th century, when most of the interstate highway system was built.

The Forbes Avenue bridge doesn’t carry interstate-highway traffic, but its construction was no doubt made easier by the abundant highway money that prevailed in the 1970s.  No bridge can last forever, and steel bridges in regions where salt is used on the roads have to be monitored with special care because of problems with corrosion.

Not being a civil engineer, I can’t tell from the news photos of the collapse just what kind of a bridge it was, but obviously it was the kind that can wear out right after its design life lapses.

Traffic on the bridge was not especially heavy at the time, so my uneducated guess is that a critical structural element simply decided to let go, causing a sequence of events that led to the failure of the whole bridge.  It will be weeks or months before forensic engineers get a chance to analyse the pieces and figure out what gave way.

Times past

But in a way, it doesn’t matter, if you look at the broad picture of bridge infrastructure in the US.  The coincidence that a President who signed a bill that is going to do something about it visited the city where a bridge collapsed the same day simply draws attention to the fact that the built environment is a measure of the society that builds it.

The society that devoted such energy to building the bridges and roads of the 1950s through the 1970s was a different society than the one we have today, and unique in many ways.

The farther we get from that era, the more unusual it looks in comparison to either the decades before, during the Great Depression when about the only public-works projects were Federal programs, and the decades after, when the rest of the world’s industrial capacity recovered after World War II and removed the exceptional economic advantages that favoured projects in the US such as the interstate highway system.

Required repairs

But our economy depends on roads and bridges to be there, so it is only doing the responsible thing to maintain them.  And last fall’s infrastructure bill was recognised as a sorely-needed act by some Republicans as well as Democrats, which is why it passed despite the huge price tag.

Only about a tenth of the $1 trillion will go to roads and bridges, but $110 billion is a good bit of the $125 billion that the ASCE says the nation’s bridges need.  It won’t “fix them all,” as President Biden said about Pittsburgh’s decaying inventory of remaining bridges, but it will go a long and useful way in that direction.

The park that the Forbes Avenue bridge spanned is named after Henry Clay Frick (1849-1919), a nineteenth-century industrialist who chaired the Carnegie Steel Corporation, and is most well-known now for his charitable bequests, such as his former mansion which became the home of the Frick Collection of fine art in New York, as well as the land which became Pittsburgh’s Frick Park.

Frick’s name is indirectly connected with a much worse disaster than last week’s bridge collapse, incidentally.  As a founding member of the South Fork Fishing and Hunting Club, a private club that named among its members many of the wealthy men of Pennsylvania, he was partly responsible for alterations of what was then the world’s largest earthen dam, holding back the waters of Lake Conemaugh, where the club members liked to fish.

Calamity

Despite warnings by engineers that the dam was defective, the club reportedly lowered the level of the dam by three feet. After unusually heavy spring rains, on May 31, 1889, the dam broke, sending most of Lake Conemaugh roaring through a valley that led directly to the doomed town of Johnstown, Pennsylvania, killing 2,200 people and devastating the town.

The disaster that happened last week in Pittsburgh was nothing like the Johnstown Flood, but there are a few parallels. Engineers knew that the bridge deck and superstructure were in “poor condition” from a recent inspection. But as it carried 15,000 people a day, they were reluctant to shut it down to make repairs, even if funds had been available.

Now the choice has been made for them, and residents of Pittsburgh are going to have to find another way to go where they’re going if they were used to crossing Frick Park on the Forbes Avenue bridge.

But President Biden pointed out that Pennsylvania is slated to receive $1.6 billion over the five-year span of last fall’s infrastructure bill, and surely that will help to repair not only the Forbes Avenue bridge, but others that are time bombs set to collapse at an unknown date in the future.

Republished with permission from the Engineering Ethics blog.

Karl D. Stephan

Karl D. Stephan received the B. S. in Engineering from the California Institute of Technology in 1976. Following a year of graduate study at Cornell, he received the Master of Engineering degree in 1977