Recently visited San Francisco, and among other activities I took a stroll on the Golden Gate Bridge.
That bridge is now 80 years old.
Hoover Dam is 81 years old.
The Mackinac Bridge is 60 years old.
No doubt these and other famous infrastructure items are well-maintained, but in the end, entropy wins: everything wears out someday. How long before the powers-that-be decide that maintenance/repair is no longer feasible (e.g. a main suspension cable is no longer trustworthy, or the cracks in the dam are too many/too deep), and it’s time to tear that sucker down and put in a new one?
Did the designers specify an expected life span when these things were built?
The British built the Aswan Low Dam ( Old Dam ) in 1898, the largest in the world, plus later additions; although superseded by the High Dam ( planned from 1912 ) in the 1960s, it’s still standing.
The researchers found some defects such as moderate to severe honeycombing, and some medium to large cavities. These cavities were deemed construction flaws, which made the dam permeable at the outset. Nonetheless, the tests that measured compressive strength, modulus of elasticity, shear strength, tensile strength, specific gravity and water adsorption show that the masonry is in good shape. *
Vladimir Novokshchenov, Consultant; Concrete Clinic International, Wexford, PA,
I don’t know the Egyptians’ maintenance schedule, but like the pyramids, massive amounts of rock and clay aren’t going any place soon.
The biggest dams, bridges, roads etc can only ever atract the money needed to build them if they have the potential to be regional or national economic game-changers.
As the OP noted we are in centenary territory for some technologies for the first time ever.
The structures may be holding up okay for the first century, which probably means that with care and attention they will have several hundred more years of life, but the purpose they were intended to serve may have altered beyond recognition, and may even make the structure redundant.
One aspect of future-proofing is the ability to build for future capacity. Its incredibly hard to justify building something now so it can serve an expected increased demand in 50 years. One good example is the Sydney Harbour Bridge which was built waaaay above capacity in the 1930s, but really only got peak hour congestion half a century later. A bridge serving the 1930s demands would have been redundant within a couple of decades, and required replacement, and may already have been unable to be built because of changed environmental and social expectations.
I’m sure I read somewhere that the concrete in the Hoover dam is still not fully cured all the way, if so it seems to me it will actually get stronger before it gets weaker
More accurately, certain spots will be getting stronger/harder. Meanwhile, other spots are developing cracks or shifts or water is undermining the foundation in spots.
The “strength” of the total structure is that of whichever part fails first. The fact some other parts are super-duper overbuilt doesn’t add to the total strength once that failure happens. Still-hardening concrete down in the bowels is an example of that same “overbuiltness”.
IOW, that speaks to one stouter-than-average link in the chain.
A better example is the Brooklyn Bridge (One of the first mega projects)
This is a bridge where sections of it are 150 years. It has gone through extensive renovation and refurbishment and is still in as good shape as it was when it was built originally
However, as mentioned in many posts, it is not these landmark items that I would be concerned about, Moreso, the smaller local bridges and dams that were don’t get the attention of these mega projects.
NC outerbanks Bonner bridge is 54 years old and in very bad shape. It’s being replaced now , new bridge opens in 2 years. Traffic is about 4000 cars per day.
It was built on the cheap but the new bridge is much higher quality.
Wouldn’t the Nile be keeping the Aswan Dams rather wet ?
Quite apart from the Hoover Dam, which was a fine work, and also as hot as Egypt, I’m sure engineering of the 1930s outperforms engineering of the 1890s, because of increased skills and materials.
Oddly, whilst a minimum of 100 American workers died on old Hoover ( some causes weren’t included — as is normal practice among rascals ), the High Dam 30 years later may have claimed 500 deaths in it’s construction. I cannot find any deaths for the 1898 Low Dam; but there were bound to be some. This was the period of the Franco-American Panama Canal.
Certainly the Aswan dams are subject to the same water-related concerns as are any dams. It was your “like the pyramids” sidebar I was mostly reacting to.
My point was the longevity of the pyramids exposed only to gravity & wind says little about the longevity of earthen dams exposed to gravity and water and differential water pressure. Same materials + different environment => different outcome. It seemed to me you were arguing otherwise. Sorry if I over-interpreted what you meant.
Dunno, however in the French period I know they only counted deaths that occurred in hospital, as with my mention of the Hoover deaths being selective. I think in the American period fewer Americans died, but the locals just kept dropping like flies.
As a child, a snippet in a Victorian popular magazine regarding the opening of a cement block in Tangier showing that St. Geronimo really was drowned that way in Algiers by the Muslims in the 16th century kept me from sleeping.
Liquid plaster of Paris was run into the mould left by the saint’s body, creating a perfect model showing the features of the youth, the cords which bound him, and even the texture of his clothing. This model was said to be held in the museum formerly at Parc du Galland, Mustapha Superior, Algiers.*
That is one exhibit I would never look at.
The Brooklyn Bridge is now 130 years old and doing fine. But the adjacent Manhattan bridge, now only 108 years old, not so well. The problem is the torsion effect from the subway trains that pass over it, twisting the girders. The Brooklyn bridge, as the first megabridge was heavily over designed.
The Sydney Harbour Bridge is a good examples: the tram lanes were re-purposed as traffic lanes, and the speed of transit increased dramatically with automotive technology. Or take the London bridges: capacity was increased by removing buildings.
I don’t know that it’s ever been common to build bridges with “spare” capacity.