NOVA: "Why Bridges Fail" (Windfall Films, BBC, PBS, 2019)

by Mark Gabrish Conlan • Copyright © 2024 by Mark Gabrish Conlan • All rights reserved

Last night (Wednesday, May 8), after the “Tomorrows” episode of A Brief History of the Future, KPBS showed a NOVA episode called “Why Bridges Fail” that was built around the spectacular collapse of the Morandi Bridge in Genoa, Italy. (The bridge was named after its designer, Riccardo Morandi.) Most Americans have either never heard of Genoa, Italy or know it only as the birthplace of Christopher Columbus. The Morandi Bridge, also known as Viadotta Polcevera, was built in the 1960’s (according to Wikipedia, from 1963 to 1967) across the Polcevera River on the A10 freeway. On August 14, 2018 a nearly 700-foot segment of the bridge collapsed and fell about 100 feet to the canyon below. The accident killed 43 people, though amazingly some of the drivers on the disintegrated segment survived the fall and two of them were interviewed for this program. Though the bridge didn’t visibly sway during storms like some other famously collapsed bridges, there was enough preliminary concern about how much the increasing flow of traffic was wearing out the bridge that starting in the early 2000’s there was already talk of tearing down the bridge and building a replacement just north of it. Before that there were attempts at patching it and trying as best as possible to reverse the corrosion of the internal metal within the pre-stressed concrete of which the bridge was made. Starting in the 1950’s bridge builders had moved away from suspension bridges as the way to cross large water or canyon barriers and instead were moving towards reinforced concrete blocks with steel rods inside to support them and give them durability. This only worked if the steel rods could be kept absolutely water-tight because water seeping into the concrete through cracks or other imperfections could rust the steel rods, causing them to lose structural strength and, in extreme cases, to collapse altogether.

The show mentioned other bridges that have been in danger of collapse, including one called the Hammersmith Flyover in London, which was successfully kept up by installing new steel barriers along the sides of the bridge and cladding them in watertight coverings. Ironically, according to the Wikipedia page on the Morandi bridge, Morandi himself had suggested a similar fix for his own bridge in 1978, when he wrote, “I think that sooner or later, maybe in a few years, it will be necessary to resort to a treatment consisting of the removal of all traces of rust on the exposure of the reinforcements, to fill the patches with epoxidic-style resins, and finally to cover everything up with elastomers of very high chemical resistance.” One of the odder things the structural engineers in London did with the Hammersmith Flyover was they literally bugged it: they installed 500 microphones under the bridge to record the sound of the concrete supports snapping apart inside. The reason was to document that the bridge would literally collapse without the extensive (and expensive) repairs the engineers were calling for. One of the points made in this documentary, directed by Martin Gorst, was that most of America’s interstate highway system was also built in the 1950’s and 1960’s and therefore all its elaborate bridges – including the ones that crossed, not water, but other freeways in overpasses and cloverleaf intersections – were also subject to the same strains as the ones that collapsed the bridge in Genoa, especially since freeways all over the world are simply carrying far more cars and trucks (and the weight of them) than they were designed for.

Suspension bridges have potentially similar longevity problems, as Gorst showed when he included documentary footage on the construction of the Golden Gate Bridge from 1931 to 1936. It showed how the giant suspension cables from which hangs the bridge’s roadway were made: literally thousands of steel rods about an inch thick were woven together, then covered in a now-iconic red waterproof coating that gave the bridge its fabled color. Unfortunately, the waterproof coating was not as waterproof as advertised; over time, especially for a bridge that spans a major and well-traveled waterway (the San Francisco Bay), water has seeped in and started rusting the steel rods from inside. To stop this, engineers worked out an unusual fix: to blow air at very low pressure inside the cables, thereby drying them out. If nothing else, “Why Bridges Fail” was an important and timely lesson in the need to repair and maintain infrastructure continually. You can’t just build it and forget it; you have to take care of it over time and correct both for natural wear and tear and unexpected problems, including the sheer amount of traffic modern life generates. “Why Bridges Fail” ended with a note that Genoa dedicated a new bridge across the Polcevera in August 2020, which made me wonder whether they just replaced the missing part of the Morandi Bridge that collapsed or they tore it down and built a new bridge. According to Wikipedia, they tore it down and built a new bridge, demolishing the old one from February to June 2019 and starting its replacement, the Genoa-Saint George bridge, on June 25, 2019. It was finished by spring and formally opened on August 3, 2020 – surprisingly quick work for we Americans, who are all too used to infrastructure projects stretching out seemingly forever!