Wednesday, March 27, 2024

A "Cathedral of American Infrastructure" - gone in a few seconds

I learned about the bridge collapse the old fashioned way: by word of mouth. On my early morning walk at 6am my neighbor stopped his pick up truck, rolled the window down and said, "the Key Bridge is gone". With that he showed me the video clip of the ship ramming the pier and the immediate collapse. "All gone" he said, and added "be safe" before he drove on to his work. 

Francis Key Bridge, a "Cathedral of American Infrastructure"

Later on this calamitous day the Mayor of Baltimore, the Baltimore County Executive, Congressmen, the Secretaries of the State and federal Transportation departments and even the President himself expressed their shock about what had happened. 

DOT Secretary called the bridge a "cathedral of American infrastructure" and with that adequately expressed the meaning of the bridge in the minds of people in Maryland and beyond for whom this bridge was an iconic landmark that was visible from many vantage points. One could stand in Patterson Park and if the weather was good clearly see the Key Bridge. Seeing it added value to real estate like like seeing the Washington Monument in DC or the Eiffel Tower in Paris. The industrial touch was apt for this industrial legacy city with a proud history in steel, right next to the bridge at Sparrows Point which is currently being reborn as a distribution/manufacturing and shipping center. The New York Times observed that "the Key, with its gently sloping arch and views that no tunnel could match, had become an emblem of Baltimore’s identity as a working port city". Former Mayor Kurt Schmoke called it a "blue collar bridge". Those blue collar workers are now facing an uncertain future as long as the shipping channel remains blocked and access to Sparrows Point limited.  

For now the giant container cranes of the port of Baltimore have to act as the stand-ins, their line up clearly pointing to where the bridge is now missing with the jarring ramps pointlessly reaching up to the void. 

A clip from the video showing the bridge buckling

The collapse caused waves around the globe. For a day it became top news in many media and TV outlets, nationally and internationally. German TV sent their reporter from Washington to Baltimore for a live report on site, Spanish noticias brought a Spanish engineer into view who explained why their biggest bridge, the Puente de la Constitución de 1812 in Cádiz would not experience the same fateFrench TV at one point focused entirely on the ship and how it was unheard of that all its systems would fail at the same time. British tabloids had engineers explain the flaws of the continuous truss bridge design.

This is a remarkable effect, in part owed in part to the unique coincidence of events which never have happened like this before, in part due to the sheer size of both the bridge and the ship for which it was no match. The Dali is 985 feet (300 meters) long and about 157 feet (48 meters) wide and weighed with cargo about 115,000 tons. The global response also speaks to both, the power of design and engineering as much as to their weakness when it comes to the most daring design and engineering endeavors. 

The world was shocked when the Hindenburg burnt, when a manned space shuttle disintegrated in space and when two regular airliners brought down the twin towers of the World Trade Center and in each case the shock seems to have been a mix of mourning for the lost life and utter astonishment that things can fail so spectacularly. The more awe inspiring a design is, the bigger the shock when it gets destroyed. 

The bridge, the giant ship and the idled port (BBJ)

The Key Bridge was awe inspiring because its tall arched steel truss could be seen for miles and was very impressive when traversing the bridge in a car, high up above the water with the skyline of Baltimore in the distance. And this design was also impressive for engineers, the truss was reportedly the third longest continuous steel truss span in the world and the second longest in the US. Construction began in 1972 and the bridge was opened to traffic on March 23, 1977 as the last piece closing the Baltimore Beltway I-695. Including its connecting approaches, the total project length encompasses a 10.9-mile corridor. Of course, now the impressive truss becomes a liability since the design lacked redundancy. Lacking redundancy generates elegance but also increases vulnerability.

'When you take away one of the supports you get a catastrophic failure because all those parts that are interconnected suddenly become overloaded,' Julian Carter, a Fellow of the UK Institution of Civil Engineers as quoted in the British Daily Mail
The fallen bridge still blocks the port of Baltimore and with it vital shipping of bulk cargo, cruise ships and also container shipping which is generally not Baltimore's main staple. Finding the victims of the collapse in the water is the first priority. Once again highway maintenance workers died while doing work on the beltway. Then clearing the shipping channel will be urgent. While everyone in this region knew the Key Bridge, many only now learn how important Baltimore's port is for this region and far beyond.
The technical aspects of the bridge (Daily Mail, UK)

The president highlighted that the Port of Baltimore is one of the nation's largest shipping hubs and that it handled a record amount of cargo last year. He added that 850,000 vehicles go through the port every single year, 15,000 jobs depend on the port, and 30,000 vehicles cross the bridge on a daily basis (The Hill)

Soon enough minds will turn to designing a replacement bridge, which will likely take years. Should speed win over esthetics or should the new bridge strive to be iconic once again? Designing a bridge spanning the shipping channel high enough for tall ships to clear cannot be done with a ready to go standard highway bridge design. Most likely the specifications alone will make a new bridge also remarkable and eventually a new landmark, whether it uses steel trusses or cable trusses or some other technique. Maybe a temporary low structure that would be opened up for ships to pass could take some pressure off a new final bridge design which most cost effectively would connect to the still standing approach ramps. 

Certainly lessons will be applied, none of them simple or cheap. The first place to apply lessons may not be a new Key Bridge but the nearby Bay Bridge double span as well as the far away Oakland Bay Bridge, the Delaware Bridge and many others which appear to be equally vulnerable. 

Only if the new connection would be a tunnel would it not be a landmark any longer, but a tunnel wouldn't solve the issue of hazardous cargo that is prohibited on all tunnels, including the already existing tunnels under the Baltimore Harbor.

Spanish Cable Stayed Puente de la Constitución de 1812 in Cádiz 

“I do not know of a bridge that has been constructed to withstand a direct impact from a vessel of this size,” DOT Secretary Pete Buttigieg
He may well be right. The force from a 115 000 ton ship moving at 9mph is beyond any impact force that is in the current design guidelines for bridges. From 1960 to 2015, there were 35 major bridge collapses worldwide due to ship or barge collisions, according to the World Association for Waterborne Transport Infrastructure. Redundancy in the bridge design would make a collapse less likely or allow a partial one versus a total collapse. Stronger pylons would withstand bigger impacts and guideposts and floating "dolphin" barriers may direct ships away from pylons. Keeping tugboats steering the ship until it passed the bridge maybe another option. One can hope that engineers and designers rise to the occasion. But no design will ever be able to prevent failure against what was not calculated or anticipated. 

Klaus Philipsen, FAIA

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