How is the structural integrity of very old buildings, bridges, etc. tested to ensure suitable use by people, cars, etc?
In: Engineering
Survivor bias: If they are still around then you can expect them to be overbuilt. All the crappy stuff fell down decades ago.
“Okay Joe bring one more elephant up here” crash. “Yup that bridge was only 4 elephants strong”.
My job deals with bridges. We instrument the bridge to record it’s behavior then we drive trucks over the bridge with different weights. Then the engineers look at the data and can decide on a load rating for the bridge and it’s health. We’ll do this for any bridge and also long term monitoring on some structures to watch for degradation.
It depends on your country’s level of development. In the US a civil engineer will calculate load density maximums using an algorithmic formula based on the structures building materials and overall design. They will also use a tool called a dinglemomiter to ‘ding’ the structures main support beams. The dinglemomiter will read out important data that allows them to estimate the core tensile strength of the supporting structures material. In the end it is all an educated guess, so they typically leave tons of room for error.
In other places around the world, they pick the most gullible person nearby to get in a heavy truck and test it the old fashion way.
If you read the first paragraph and beleived it, then I’ve got the keys for you.
When I visited Hagia Sophia in Istanbul the guides showed us a section of wall that had glass slats mortared in. They explained that the building’s stewards would check the slats after any earthquakes to see which walls were shifted and where to make repairs based on which of the glass slats broke. The Hagia Sophia was built in 537. When you consider the cost of glass in relative prices for the time, this safety measure was a significant investment.
There was a Pbs special on it, discussing modern approaches for stabilizing the building. If you can find it they talk about all the modern engineering improvements they’re trying to bring in to the structure without compromising its antiquity too much.
I’m a Civil Engineer too from Brazil, let me just mention something.
It’s very usual here to have old buildings which you haven’t got the structural plans to, and you can’t guarantee the original builder followed the codes of the time (they don’t even follow it now.)
So one technique that’s particularly interesting to test the strength of the concrete is that you can cut a cilinder out of a few columns (there are places in the column that you can do this safely) and test that cilinder’s strength on a concrete press. This tells you how strong the concrete is, and you can close the hole with stronger concrete later.
This is called destructive testing, and there are many non-destructive methods available, but this is a fairly straightforward as many labs would have a concrete press.
Of course this doesn’t cover the steel reinforcement, but as was already said that can be evaluated by other techniques.
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