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The problem with reinforced concrete (2016)

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Re: The problem with reinforced concrete (2016)

#111

Post by robocat »

diegocg wrote: post #65
raylad wrote: post #48

Earlier quoted context omitted.

It should be but is it? I don't think anyone ever tested this building, which has a combined market value of probably close to $200M. None of the owners want to know that their investments are worthless. So nothing will be checked unless its required by law.

In Spain buildings older than 50 years are required to be inspected and mandated to make reforms if necessary. I doubt it's much different in the rest of Europe/north America Also, buildings don't fall all of sudden. You would get a lot of cracks and problems before your building collapses

> Also, buildings don't [fail] all of sudden

They certainly do in earthquakes. Even in areas that nominally don’t have earthquakes, some parts of the building code will surely be about ability to withstand a rare earthquake.

Re: The problem with reinforced concrete (2016)

#112

Post by brandmeyer »

mardifoufs wrote: post #74
peteradio wrote: post #64

Earlier quoted context omitted.

That doesn't smell right. I've got 15 year old knives that have never once shown signs of rust. A pair of old scissors left in the rain rusted in under a day. That puts the factor to closer to >10000 than 10 or 100...

There are different grades of stainless steels. The common, "construction" grade stainless steels usually rust albeit very slowly. And while some of them are basically impervious to corrosion, they are usually way more expensive or have a lot less tensile strength. I don't know about knives specifically but it wouldn't surprise me if those more corrosion resistant grades are what's used to make them.

Example: The Gateway Arch was surfaced with a stainless steel alloy, and it is suffering some corrosion problems today.

Re: The problem with reinforced concrete (2016)

#113

Post by brudgers »

Every human is valuable. Every human has opinions. But every human’s opinions are not equally valuable.

Their are two reasons for steel reinforcing. The steel can withstand tension and concrete can’t. Even worse concrete in tension fails catastrophically, the steel insures it fails ductally.

Masonry had exactly the same problems and all modern masonry structures are reinforced masonry...reinforced with steel, Just like concrete.

Aluminum and other potential reinforcement materials are less suited than steel because steel and concrete have similar coefficients of thermal expansion. Yes steel can corrode and expand and spall concrete. Other materials will spall concrete simply from seasonal and diurnal changes in temperature.

Concrete designs are engineered and like all engineered systems, there are trade offs between cost and performance. And like any design, use may exceed or deviate from specified design parameters.

Re: The problem with reinforced concrete (2016)

#114

Post by culturestate »

WalterBright wrote: post #85
matheusmoreira wrote: post #16

Earlier quoted context omitted.

How can I know if a building was designed to last a long time? Is it the materials, the method of construction?

One way is to see how the building protects itself from water. Water is the great destroyer of buildings. A flat roof, for example, is very prone to leaking, which when not constantly taken care of will wreck the building. Another is if the roof keeps water off of the walls (how big the overhang is). Many buildings have eaves that are an inch or two. The exterior walls of these buildings won't last. Any building on a…

> Many buildings have eaves that are an inch or two. The exterior walls of these buildings won't last.

Unless you’re talking about a very old house, this depends a lot on the local climate, construction materials, and design.

You can pretty successfully mitigate water entry with a dimple membrane and a gutter on an exposed wall, for example, and obviously this is a minimal concern if your house is in a desert.

(I’m not a trained architect, just someone interested in building science.)

Re: The problem with reinforced concrete (2016)

#115

Post by lmm »

mortenjorck wrote: post #98
mc32 wrote: post #89

Earlier quoted context omitted.

Japan builds buildings to last 30 years on average. They tear them down and build new ones. Is it good, bad, something else? I don’t know, except not everyone builds for things to last a long time.

People quote this figure often, but it really only applies to detached single-family dwellings, which are commonly built for a single owner. Japan certainly doesn't build larger structures such as office buildings for thirty-year lifespans – no one has floated any plans to tear down the Kasumigaseki Building yet: https://en.wikipedia.org/wiki/Kasumigaseki_Building

One historic building being 50 years old proves very little - of course some buildings last longer than the average. E.g. every one of the famous Dojunkai apartment buildings has been demolished.

Re: The problem with reinforced concrete (2016)

#116

Post by WalterBright »

culturestate wrote: post #114
WalterBright wrote: post #85

Earlier quoted context omitted.

One way is to see how the building protects itself from water. Water is the great destroyer of buildings. A flat roof, for example, is very prone to leaking, which when not constantly taken care of will wreck the building. Another is if the roof keeps water off of the walls (how big the overhang is). Many buildings have eaves that are an inch or two. The exterior walls of these buildings won't last. Any building on a…

> Many buildings have eaves that are an inch or two. The exterior walls of these buildings won't last. Unless you’re talking about a very old house, this depends a lot on the local climate, construction materials, and design. You can pretty successfully mitigate water entry with a dimple membrane and a gutter on an exposed wall, for example, and obviously this is a minimal concern if your house is in a desert. (I’m n…

I live in Rain City (Seattle). Quite a lot of homes are built with ridiculously tiny eaves. I'd never buy one of those.

My house has eaves that stick out about 2 feet. It added nothing significant to the cost, but boy what a difference it makes. The exterior walls almost never get wet. The windows and their frames stay dry and free of rot. No mildew. Haven't even needed to repaint.

There are a lot of things one can do with a house that, at trivial expense, will dramatically improve its life and lower maintenance costs.

Here's another one. Run the plumbing up interior walls. Then it won't freeze.

Re: The problem with reinforced concrete (2016)

#117

Post by brandmeyer »

minikites wrote: post #4
brutusborn wrote: post #3

This should be an economics piece, not an environmental piece. The author states that "one of iron’s unalterable properties is that it rusts" yet further on acknowledges the existence of stainless steel. There's nothing wrong with reinforced concrete, but the incentives to produce long lasting buildings are not there. The cheapest bidder will generally win and their building will last the "design life" of the buildin…

Is it a good thing for society to directly incentivize the construction of longer lasting buildings?

One reason to prefer shorter-lasting buildings is to encourage higher density over time.

Re: The problem with reinforced concrete (2016)

#118

Post by _jal »

peteradio wrote: post #64
wahern wrote: post #29

Earlier quoted context omitted.

> The author states that "one of iron’s unalterable properties is that it rusts" yet further on acknowledges the existence of stainless Even stainless steel rusts, just more slowly. Roughly 10-100x more slowly, judging by https://www.nrc.gov/docs/ML1124/ML112490377.pdf and https://www.mdpi.com/2076-3417/10/23/8705/pdf .

That doesn't smell right. I've got 15 year old knives that have never once shown signs of rust. A pair of old scissors left in the rain rusted in under a day. That puts the factor to closer to >10000 than 10 or 100...

There are different grades of steel, doped with all sorts of additives, depending on the desired traits. The most corrosion-resistant variant today used in knives would be one of the nitrogen steels, like Nitro-V.

https://knifesteelnerds.com/2019/09/23/nitro-v-its-propertie...

But they all corrode, eventually. If you want a true corrosion-resistant metal that stays (kinda) sharp, look at one of the cobalt alloys like Stellite.

Re: The problem with reinforced concrete (2016)

#119

Post by LegitShady »

oxfeed65261 wrote: post #69
GoToRO wrote: post #40

Earlier quoted context omitted.

I spoke with a builder, and the concrete starts to decay in 50 years. Until then it's like new. It lasts much longer than that, 100+ years is not a problem.

To be clear, the article is discussing reinforced concrete—concrete made with steel rebar, which rusts. Unreinforced concrete can and does last for many hundred years. Reinforced concrete, not so much. FTA: “Early 20th-century engineers thought reinforced concrete structures would last a very long time – perhaps 1,000 years. In reality, their life span is more like 50-100 years, and sometimes less. Building codes and…

Unreinforced concrete is largely useless for modern construction, because it basically has negligible tensile strength. You can't make beams, columns, or even pre-fabbed wall panels of any useful strength without reinforcement.

One of the reasons unreinforced concrete may last a lot longer is because its only going to exist in places that don't subject it to tensile stresses. That being said, changes like differential settling can create these stresses after construction.

'Deterioration' can mean many things in terms of concrete.

Re: The problem with reinforced concrete (2016)

#120

Post by anitil »

chairmanwow1 wrote: post #8
dmckeon wrote: post #2

No mention of epoxy coatings for steel rebar? Look for green-coated rebar as you pass highway construction sites.

For some reason I stumbled across a wild YouTube channel by a guy named Tyler Ley that is “crazy for concrete”. If I remember correctly he’s a civil engineering professor and has a lot of fascinating videos about concrete. In particular one about epoxy coated rebar that gives interesting notes about why it has its problems: https://youtu.be/xVDy84rR5Z8 I had a great couple of days learning all about the complexities…

He is fantastic! I was really struggling to find his name again.
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