How is the structural integrity of very old buildings, bridges, etc. tested to ensure suitable use by people, cars, etc?

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How is the structural integrity of very old buildings, bridges, etc. tested to ensure suitable use by people, cars, etc?

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16 Answers

Anonymous 0 Comments

The most basic is looking for deterioration, looking for where corrosion has occurred, bricks fallen mortar cracked, and can get a general idea of the condition. Tension cables can be tested for how much tension they’re under, and can have electrical current run through to check for corrosion.

Anonymous 0 Comments

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Anonymous 0 Comments

Civil engineer here. For old buildings, if they have the architectural plans then they can usually derive all the mathematical info they need and account for decayed members. If they don’t, they’ll try to generate one and usually schedule renovation. That’s mainly for old buildings like houses. Bridges can be tested for a variety of factors – they use a lot of deflection analysis, so like seeing how much a bridge will sag under a given load, or how much it’s cables (assuming suspension bridge) extend under that load. A lot of visual analysis occurs as well – cracks, rusty rebar, split timbers can all indicate the current state of the structure and can be accounted for in projections of how long it will last based on modeling. Other methods can also be used to look for wear *inside* a structure, like using electrical pulses or vibration feedback on concrete. Also, because building codes are so meticulous and regulated, a good inspector can actually refer to old building manuals and practically determine from those what kind of design life a structure was built for. It’s a fine-tuned skill and one of the aspects of civil engineering that is highly valued because of the experience it requires.

My timber design professor was such a knowledgeable guy that he was brought in to inspect why a frame holding a very expensive painting fell, and it didn’t even take him long to figure it out.

Honestly it’s pretty cool. Good question!

Anonymous 0 Comments

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Anonymous 0 Comments

Buildings are designed to signal you that it will be on the end side of its usefulness. For example in concrete, The best one to see it is by crack. Engineers will observe it by how the cracks looks like. Cracks doesn’t mean painting cracks though, but on a different kind. There are various kinds of it and it will say if the building is failing and we have checklist for that as ASCE dictates(or whatever governing codes on your area).

A 12inch of ruler is an example. If you bend it too much in the middle, notice the crack. That may how it looks like in the reality. Then try to break the first one inch of it, that’s what we call shear failure. It’s hard to bend the ruler if you use the deeper side than the thinner side right? We call it stiffness and its important in deflection.

There’s a local code in your area that will tell you when are you going to need an evaluation for this. If its historical building, retrofitting is a hundred percent needed.

Anonymous 0 Comments

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Anonymous 0 Comments

On the back of this, are they periodically checked? A bridge in Nottingham has been declared unsafe as they found rust in the support s or something, I’d like to know how and why they found out.

Anonymous 0 Comments

What about huge buildings like the John Hancock in Chicago? What is the lifespan of a place like that?

Anonymous 0 Comments

I used to inspect bridges!

Short answer: We look for cracks.

Cracks, and “efflorescence,” which looks like concrete icicles or milk stains under concrete structures. (rain + chemical reaction = salt leaking out of concrete: makes it weaker)

The *underwater* portion is what made my team pretty unique. We would get a guy in scuba gear and have him check the underwater portion of the pilings (pile-ings)/pillars. The water (and anything floating in it) wears on those piles, so we keep an eye on that wear.

The scuba bro sent back information via built in headset radio and his buddy in a small boat (me!) tends his line and takes notes on his findings. Hope that helps 🙂

Anonymous 0 Comments

Structural engineer with experience in retrofitting and historic preservation: For low level stuff like houses you normally don’t outside of very unusual jurisdictions. These are basically grandfathered in and providing you don’t make any significant renovations or the building doesn’t get damaged they’re allowed to continue in use on the basis they’ve been there for a loooong time, even if they wouldn’t meet current code.

For bigger things – train stations, bridges, large multi story buildings: Almost all of the things like this built since the industrial revolution were engineered to an extent and often drawings are available. For the most part they keep getting used as-is until there’s a change in use that warrants an engineering assessment. In the US this is if there’s more than a 5% increase in gravity loads or 10% increase in lateral loads (code proscribed). So say you want to convert an old apartment building into office space – the code loads are higher so you’ll need to do an assessment. There are a fair number of codes and industry documents around that give guidance on how to approach these evaluations in a manner consistent with current practice.

To do the analysis you find whatever existing drawings you can – these can be surprisingly detailed and will even give material strengths. If there are gaps in the drawings, missing drawings or there have been renovations since you do field verification of the structure, including material testing to determine the strength of the brick, concrete, steel, iron, timber etc that makes it up. There is also a decent volume of information available to help with this – eg – for older steel in the US you can get a publication that lists the exact section sizes each major mill produced (they used to all vary) based on the construction year, along with the documented strength of steel used – you can go look at a beam until you find a mill mark (they’re frequent) then take the construction year and you’ll be able to looo up fairly precise member properties. Then you take the information and analyze it and determine the code load rating, and then strengthen if necessary.

A lot of the time buildings built during this era have a fair amount of spare capacity as the loads and designs used were conservative, but once in a while you find something that’s an edge case.

Bridges: If the use changes – you want to permit bigger trucks, or it gets damaged/modified you do the same, generally with a lot of field investigation as the structure is often exposed, which means it’s more subject to corrosion or other damage.

For older stuff – pre industrial era – you’re normally looking at some combination of masonry and timber only. These are well understood materials. Original drawings are rare, but most of the time the buildings are structurally fairly simple (things like churches and other monumental buildings aside) so can be investigated fairly easy making a few informed assumptions with knowledge of the construction practices of the time. These types of construction though are normally inherently very robust unless you’re facing earthquakes and it’s mostly just floors that need review unless you’re doing something massive to the building.

TL;DR – you (normally) don’t unless you’re changing something or carrying out structural repairs, and then you have an engineer investigate and analyze it.