08/20/2018
Our Crumbling Infrastucture
Following the tragic collapse of Genoa bridge, The Economist had some of the following thoughts on infrastructure in an editorial.
“A report from the American Road & Transportation Builders Association in January is even more sobering. It reckoned that 54,259 of that country’s 612,677 bridges are ‘structurally deficient.’ These problem bridges have an average age of 67 years and are crossed by vehicles 174m times every day. At the present rate of repair and replacement, it will take 37 years to remedy all the problems, says Alison Premo Black, the organization’s chief economist.
“What is going wrong with these bridges? The difficulty is that concrete, or rather the steel used to reinforce it, can fail in a number of ways. Salt, ice and the pounding of weather can cause tiny fractures in the concrete’s surface. As these cracks creep inward, they let in water. Once the water reaches the steel reinforcing or tendons, it corrodes them. This enlarges the cracks, which can cause the concrete to fall apart. That this is happening is evident from rusty streaks on crumbling concrete.
“Other factors compound the deterioration of bridges, such as constant cyclic vibration from traffic, says Mehdi Kashani, an expert in structural mechanics at the University of Southampton, in Britain. This is troublesome for bridges designed in the 1960s, when traffic flows were lower, cars were smaller and lorries much lighter. On top of that, extreme weather can take a toll, with heat and cold expanding and contracting the structure, floods eroding away foundations and high winds buffeting the bridge. This is why regular inspections and maintenance are essential....
“Monitoring and repair are not the only options. When bridges were being built in the 1950s, 60s and 70s, many were expected to last for more than 100 years. But the decay of reinforced concrete leads some civil engineers to think that such bridges are coming to the end of their days. Refurbishment is possible, but it is slow and very costly. It might end up being more expensive than building a new bridge.
“New structures can also take advantage of advances in engineering. There has been huge progress in materials science, so much so that it is now possible to tinker with the internal structure of substances to make concrete more robust and steel better at resisting rust. Ultra-high-performance concrete is already being made in some countries to toughen buildings against such things as earthquakes and bombs. Apart from just sand and cement, other ingredients are added to these super concretes, such as quartz and various reinforcing materials. In some tests, the addition of plant fibers has been shown to produce markedly stronger concrete....
“Wholesale replacement of elderly bridges would be an expensive exercise, however. The Governor Mario M. Cuomo Bridge, which opened as a replacement for the old Tappan Zee Bridge which crosses the Hudson River in New York...is also a cable-stayed bridge, but one of a more traditional design. It is expected to cost some $4bn. The old bridge, built largely from steel and concrete in the 1950s, was knocked up for some $60m, which in today’s terms would be a bargain $564m. The Tappan Zee Bridge was predicted to have a lifetime of only 50 years; it managed nearly 62. Its replacement is supposed to last for a century. Time will tell.”
Your editor traveled on the Tappan Zee every day for nine years. Absolutely hated it.
Wall Street History returns in a few weeks.
Brian Trumbore
