Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The problem with reinforced concrete (2016)

theconversation.com

Post reply on HN
Print view View original

101–110 of 192 posts

Re: The problem with reinforced concrete (2016)

#101

Post by mc32 »

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

Have things changed in the last decade or so[1]?

Japanese loathe “second hand” stuff if they can avoid it. This includes property. The service life for buildings is 47 to 50 years or so, for depreciation purposes.

Totally unrelated, but I love that 1000 year old wooden temples get rebuilt every 20 years or so[2] because of the religious idea of renewal.

[1] https://japanpropertycentral.com/2012/06/what-is-the-lifespa...

[2]https://chrispythoughts.wordpress.com/2012/10/19/558/

Re: The problem with reinforced concrete (2016)

#102

Post by fnord77 »

quickthrowman wrote: post #43
alcover wrote: post #9

There are also interesting new methods to monitor corrosion Then what ? Can you repair or replace parts of a building ?

Yes, why wouldn’t you be able to repair replace parts of a building? You cut out the bad parts while reinforcing structural elements temporarily while the replacement work is performed, then you remove the temp supports. New footings, beams, walls, etc are constructed or installed to replace old ones all the time. Say you have a bad concrete footing for a post. You use jacks to support the beam on both sides of the p…

I saw this done in downtown SF to the old macy's men's building. they cut off the facade, cut the concrete back a bit but left the old rebar protruding some and grafted new concrete/rebar on to it.

Re: The problem with reinforced concrete (2016)

#103

Post by jandrese »

renewiltord wrote: post #41
nerdponx wrote: post #20

Earlier quoted context omitted.

> The present value of a building that lasts 50 years is not that much different that the same one that lasts 100 years. That's a problem in and of itself, IMO. Construction is tremendously resource-intensive. We should not be building "throwaway" buildings.

The classic problem is similar to that of that other famous future-proof thing: wifi in hotels. All the fancy hotels that got high-end wifi in the 2000s had shitty Internet for a long time because it was too hard to redo. Sometimes, building to throw away is the best model. If something is so resource intensive in a way where the externalities are not appropriately mitigated, the right way is to tax the externalities…

Although the hotels that hardwired RJ45 to each room are still going strong.

Re: The problem with reinforced concrete (2016)

#104

Post by dylan604 »

sgillen wrote: post #72
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...

Maybe if you want to invalidate those studies you can try leaving the knives out in the rain 10-100 days in a row!

Only if you live in a rain forest.

Re: The problem with reinforced concrete (2016)

#105

Post by LoveMortuus »

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.

All correct. Stainless steel is 'created' by adding chrome and a few other materials depending on the desired properties. But despite that it will still rust.

I think a good analogy world be eating healthy, you'll probably live longer then soon-to-be who doesn't eat healthy but in the end both will die and seize to exist.

Material science is incredibly interesting field and I think it will play a huge role in the future. It already does.

Re: The problem with reinforced concrete (2016)

#106

Post by dylan604 »

nerdponx wrote: post #20
idoh wrote: post #18

I don't know if it is really a problem, more like a tradeoff. Reinforced concrete costs less and enables shapes that are impossible without it, with the downside that the buildings last 50 years instead of 100+ years. The present value of a building that lasts 50 years is not that much different that the same one that lasts 100 years. With that in mind, it makes perfect sense to make an office building out of reinfor…

> The present value of a building that lasts 50 years is not that much different that the same one that lasts 100 years. That's a problem in and of itself, IMO. Construction is tremendously resource-intensive. We should not be building "throwaway" buildings.

If the buildings last a shorter amount of time, then more construction is needed which provides jobs. /s

Re: The problem with reinforced concrete (2016)

#107

Post by jefftk »

mc32 wrote: post #101
mortenjorck wrote: post #98

Earlier quoted context omitted.

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

Have things changed in the last decade or so[1]? Japanese loathe “second hand” stuff if they can avoid it. This includes property. The service life for buildings is 47 to 50 years or so, for depreciation purposes. Totally unrelated, but I love that 1000 year old wooden temples get rebuilt every 20 years or so[2] because of the religious idea of renewal. [1] https://japanpropertycentral.com/2012/06/what-is-the-lifespa…

> The service life for buildings is 47 to 50 years or so, for depreciation purposes.

That doesn't tell you much: in the US the lifetime of a residential rental building is 27.5 years for depreciation purposes, and 39 for non-residential: https://www.irs.gov/publications/p946

Re: The problem with reinforced concrete (2016)

#108

Post by renewiltord »

jandrese wrote: post #103
renewiltord wrote: post #41

Earlier quoted context omitted.

The classic problem is similar to that of that other famous future-proof thing: wifi in hotels. All the fancy hotels that got high-end wifi in the 2000s had shitty Internet for a long time because it was too hard to redo. Sometimes, building to throw away is the best model. If something is so resource intensive in a way where the externalities are not appropriately mitigated, the right way is to tax the externalities…

Although the hotels that hardwired RJ45 to each room are still going strong.

Right, they can stick APs in them. The point is that back then no one knew which tech would win and what tradeoff to make. Agility beats everything else except "guessing right".

Re: The problem with reinforced concrete (2016)

#109

Post by readflaggedcomm »

kortex wrote: post #81
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…

There's also basalt fiber reinforced concrete. Stronger than rebar and doesn't rust.

But steel's more ductile, so basalt-reinforcement failures are less gradual, providing less margin of safety or ability to patch repair (all things being equal). It's more similar to glass reinforcement (both available in bars, mats, and fibers), which is seeing increased use, but better than glass.

Re: The problem with reinforced concrete (2016)

#110

Post by dntrkv »

raylad wrote: post #48
diegocg wrote: post #35

Earlier quoted context omitted.

Unless you are living in a developing country, the answer to the second question should be "yes".

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.

> None of the owners want to know that their investments are worthless. So nothing will be checked unless its required by law.

That makes no sense. If I am buying property, it is in my best interest to make sure it isn't going to fall apart. Especially since if something happened due to my negligence, I would be responsible.

If you have no idea of whether or not the building is being inspected, why would you make the assumption it's not?

Post reply on HN