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Posts Tagged ‘construction

“The world is bound in secret knots”*…

It’s knot easy, but it’s important, to understand knots…

From whimsical flower crowns to carelessly tied shoelaces to hopelessly tangled headphones, knots are everywhere. 

That’s not surprising, as knots are quite ancient, predating both the use of the axe and of the wheel and potentially even the divergence of humans from other apes. After all, ropes and cords are practically useless without being tied to something else, making one of the most ancient technologies still remarkably relevant today.

But these tie-offs can be a problem, since knots actually decrease the strength of a rope. When a rope made up of multiple fibers is taut, those fibers all share equal portions of the load. However, the bending and compression where the knot forces the rope to curve (usually around itself, or around the thing it is tied to) create extra tension in only some of the fibers. That’s where the rope will break if yanked with too much force. And this isn’t a small effect: common knots generally reduce the strength of a rope by 20 percent for the strongest ones, to over 50 percent for a simple overhand knot.

Experience has taught surgeons, climbers, and sailors which knots are best for sewing up a patient, or rescuing someone from a ravine, or tying off a billowing sail, but until some recent research from a group at MIT it was hard to tell what actually makes one knot better than another… 

Which knot is the strongest? “The tangled physics of knots, one of our simplest and oldest technologies,” from Margaux Lopez (@margaux_lopez_).

See also: “The twisted math of knot theory can help you tell an overhand knot from an unknot.”

Athanasius Kircher

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As we understand the over and under, we might send constructive birthday greetings to John “Blind Jack” Metcalf; he was born on this date in 1717. Blind from the age of six, he was an accomplished diver, swimmer, card player, and fiddler. But he is best remembered for his work between 1765 and 1792 when he emerged as the first professional road builder in the Industrial Revolution. He laid about 180 miles of turnpike road, mainly in the north of England– and became known as one of the “fathers of the modern road.”

Just before his death, he documented his remarkably eventful life; you can ready it here.

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“They swore by concrete. They built for eternity”*…

Understanding how the materials we use work– and don’t work– together…

For most of a red swamp crayfish’s life, cambarincola barbarae are a welcome sight. Barbarae – whitish, leech-like worms, each a couple of millimeters long – eat the swamp scum off the crayfish’s shells and gills, and in most cases improve the crayfish’s health and life expectancy. Together, barbarae and crayfish form a mutualistic symbiotic relationship. Both species benefit from their cohabitation, and barbarae have evolved to the point where their entire life cycle, from egg to adult, occurs while attached to a crayfish.

But their symbiosis is contextual – a tentative truce. Young crayfish (who molt their shells more frequently and therefore accumulate less scum) don’t need much cleaning, and will take pains to remove barbarae from their shells. And even when molting has slowed and a crayfish has allowed the symbiosis to flourish, there are limits to barbarae’s loyalty: If there isn’t enough food for them to survive, they’ll turn parasitic, devouring their host’s gills and eventually killing them.

Like symbioses, composite materials can be incredibly productive: two things coming together to create something stronger. But like crayfish and barbarae, their outcomes can also be tragic. Rarely are two materials a perfect match for each other, and as the environment changes their relationship can turn destructive. And when composites turn destructive – as was evident in the reinforced concrete when the Champlain Towers North were inspected back in 2018 – the fallout can be catastrophic.

The history of what we now call composite materials goes back many thousands of years. For modern consumers, the most common composites are fiber-reinforced plastics (the colloquial “carbon fiber” and “fiberglass”), but perhaps the first composites in history were reinforced mud bricks. The Mesopotamians learned to temper their bricks by mixing straw into them at least as early as 2254 BC, increasing their tensile strength and preventing them from cracking as they dried. This method continues around the world today.

But by far the most commonly used composite material in history is steel-reinforced concrete. Roman concrete usage started as early as 200 BCE, and almost three centuries later Pliny the Elder included a note about what appears to be high quality hydraulic concrete in his Naturalis Historiae. These recipes were subsequently forgotten, and the material largely disappeared between the Pantheon and the mid nineteenth century. Modern concrete involves some legitimate process control: limestone and other materials are heated to around 900° C to create portland cement, which is then pulverized and mixed with water (and aggregate) to create an exothermic reaction resulting in a hard and durable object. The entire process consumes vast amounts of power and produces vast amounts of carbon dioxide, and the industry supporting it today is estimated to be worth about a half a trillion dollars.

But in spite of the fortunes that have been invested in the portland cement process (as well as in a wide range of concrete admixtures, which are used to tune both the wet mixture and the finished product), the true magic of contemporary concrete is the fact that it is so often reinforced with steel – dramatically increasing its tensile strength and making it suitable for a wide range of structural applications. This innovation arose in the mid-nineteenth century, when between 1848 and 1867 it was developed by three successive Frenchmen. In the late 1870s, around the time that the first reinforced concrete building was built in New York City, the American inventor Thaddeus Hyatt noted a critical quality of the material: through some fantastic luck, the coefficients of thermal expansion of steel and concrete are strikingly similar, allowing a composite steel-concrete structure to withstand warm/cool cycles without fracturing. This quality opened up the floodgates, and in the 1880s the pioneering architect-engineer Ernest Ransome built a string of reinforced concrete structures around the San Francisco Bay Area. From there it was history.

More than any other physical technology, it is reinforced concrete that defines the 20th century. Versatile, strong, and (relatively) durable, the material is critical to life and industry as we know it. Reinforced concrete was the material of choice of Albert Kahn, who with Henry Ford defined 20th century industrial architecture; reinforced concrete is a key part of  nearly every type of logistical infrastructure, from roads to bridges to container terminals; reinforced concrete makes up the literal launch pads for human space travel. It’s a critical component of power plants, dams, wind turbines, and the vast majority of mid- to late-twentieth century homes and apartment buildings. Its high compressive strength makes it ideally suited for footings and foundations; its high tensile strength lets it cantilever and span great distances easily.

But reinforced concrete is really only 140 years old – the blink of an eye, as far as the infrastructure of old is concerned. The Pantheon was built around 125 CE, by which time the Romans had been experimenting with concrete construction for well over 300 years. When we see the Pantheon, we’re seeing a mature method – a technology with full readiness, being used in an architectural style that’s tuned for its physical properties.

By contrast, even our most iconic steel-reinforced concrete buildings are prototypes…

Early on in the history of steel-reinforced concrete, it was known that the high alkalinity of concrete helped to inhibit the rebar from rusting. The steel was said to be sealed within a monolithic block, safe from the elements and passivated by its high pH surroundings; it would ostensibly last a thousand years. But atmospheric carbon dioxide inevitably penetrates concrete, reacting with lime to produce calcium carbonate – and lowering its pH. At that point, the inevitable cracks and fissures allow the rebar inside to rust, whereupon it expands dramatically, cracking the concrete further and eventually breaking the entire structure apart.

This process – carbonatation, followed by corrosion and failure – was often visible but largely ignored into the late twentieth century. Failures in reinforced concrete structures were often blamed on shoddy construction, but the reality is that like the crayfish and the barbarae, the truce between concrete and steel is tentative. What protection concrete offers steel is slowly eaten away by carbonatation, and once it’s gone the steel splits the concrete apart from the inside…

There are of course many potential innovations to come in reinforced concrete. Concrete mixtures made with fly ash and slag produce high strength and durable structures. Rebar rust can be mitigated by using sacrificial anodes or impressed current. Rebar can be made of more weather resistant materials like aluminum bronze and fiberglass. Or the entire project could be scrapped – after all, the CO2 emitted by the cement industry is nothing to thumb your nose at. Whatever we do, we should remember that the materials we work with are under no obligation to get along with one another – and that a symbiotic truce today doesn’t necessarily mean structural integrity tomorrow.

On composites, crayfish, and reinforced concrete’s tentative alkalinity: “A Symbiotic Truce,” from Spencer Wright (@pencerw), whose newsletter, “The Prepared” (@the_prepared), is always an education.

* Gunter Grass

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As we delve into durability, we might recall that it was on this date in 315 that the Arch of Constantine officially opened. A triumphal arch in Rome dedicated to the emperor Constantine the Great, it was constructed of Roman concrete, faced with brick, and reveted in marble.

Roman concrete, like any concrete, consists of an aggregate and hydraulic mortar – a binder mixed with water (often sea water) that hardens over time. The aggregate varied, and included pieces of rock, ceramic tile, and brick rubble from the remains of previously demolished buildings. Gypsum and quicklime were used as binders, but volcanic dusts, called pozzolana or “pit sand”, were favored where they could be obtained. Pozzolana makes the concrete more resistant to salt water than modern-day concrete.

The strength and longevity of Roman marine concrete is understood to benefit from a reaction of seawater with a mixture of volcanic ash and quicklime to create a rare crystal called tobermorite, which may resist fracturing. As seawater percolated within the tiny cracks in the Roman concrete, it reacted with phillipsite naturally found in the volcanic rock and created aluminous tobermorite crystals. The result is a candidate for “the most durable building material in human history.” In contrast, as Wright notes above, modern concrete exposed to saltwater deteriorates within decades.

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“Of course I’d like to get beyond the concrete. But it’s really difficult. Very difficult.”*…

Felix Salmon is fascinated by concrete…

Greetings from my apartment in the most beautiful Brutalist tower in New York City (sorry not sorry, I.M. Pei.) My bookshelf contains such works as “Concrete,” “Concrete Concept” and “Toward a Concrete Utopia;” on my desk is “Concrete Planet.” Tl;dr: I’m a lover of concrete, not a hater. But… it’s still very problematic. And, as you’re about to find out, much more expensive than architects and contractors might have you believe…

He goes on, in his “Capital” column for Axios, to explain…

Concrete construction no longer lasts thousands of years, like the Pantheon in Rome. Instead, its lifespan is roughly 50-100 years, thanks to the way in which modern concrete is reinforced.

That means a multi-trillion-dollar bill is coming due right around now, in the form of concrete construction that needs noisy, dirty, expensive repair. 

Why it matters: The collapse of a residential tower in Surfside, Florida is a stark reminder of how catastrophically concrete can fail. Just as the collapse of the Morandi Bridge in Genoa caused Italy to start paying much more attention to remedial infrastructure projects, the Surfside tragedy might help focus America on the urgent need to fix buildings that are nearing the end of their initial lifespan.

The big picture: As Robert Courland explains in “Concrete Planet,” modern concrete is poured around steel rebar, which gives it tensile strength. But tiny cracks — found in all concrete — cause water to start rusting the steel, which then expands, cracking the concrete. 

Photos of the Surfside basement taken before the collapse show steel rebar breaking all the way through the concrete to the point at which it is fully exposed to the salty and humid Florida air.

By the numbers: One of the most famous concrete buildings in America, Frank Lloyd Wright’s Fallingwater, cost $155,000 to build in 1936 — about $2 million in 2001 dollars. The cost of repairs in 2001 came to $11.5 million.

Similarly, repairs to Wright’s concrete Unity Temple are estimated at roughly 20 times the original construction costs, even after adjusting for inflation. 

How it works: Once rebar starts corroding, the standard fix involves jackhammering the concrete to expose the steel, brushing the steel to remove the rust, reinforcing the rebar as necessary, and then covering it all back up again with carefully color-matched new concrete. 

That labor-intensive extreme noise and dust is actually the green, environmentally sensitive solution. The only alternative is demolition and replacement with an entirely new building — something that involves a much greater carbon footprint.

Between the lines: Because concrete fails from the inside out, damage can be hard to detect. And because concrete looksso solid and impregnable, necessary maintenance is often skipped, causing massive bills later on.

Local governments are in charge of ensuring building safety, but their willingness and ability to do so varies widely. The owners and residents of concrete buildings often try very hard not to think about corrosion, just because the costs of fixing it are so enormous.

The bottom line: The amount of money needed to fix existing infrastructure (nearly all of which is concrete, in one way or another) stands at roughly $6 trillion, according to the American Society of Civil Engineers. That number does not include homes, offices and other private buildings.

If you live in a concrete building that’s more than 40 or 50 years old, it’s an extremely good idea to check carefully on just how well it’s been maintained, lest you find yourself with an unexpected seven-figure repair bill — or worse. 

Go deeper: WLRN’s Danny Rivero clearly explains the collective action problems involved in persuading condo owners to pay for expensive repairs.

The tragedy in Surfside is just one indication that “America’s trillion-dollar concrete bill is coming due,” as @felixsalmon explains.

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As we muse on maintenance, we might spare a thought for Angelo Mangiarotti; he died on this date in 2012. An architect and designer, he made an early career stop in Chicago as a visiting professor for the Illinois Institute of Technology, during which met Frank Lloyd WrightWalter GropiusLudwig Mies van der Rohe and Konrad Wachsmann. While Mangiarotti learned from them an appreciation of materials (perhaps especially concrete) and industrial process for buildings and design production– on both of which he built– he is perhaps best remembered for his insistence, borne out in his work, on “never forgetting the real needs of users.”

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“Investment in infrastructure is a long term requirement for growth and a long term factor that will make growth sustainable”*…

So it’s a problem that infrastructure here in the U.S. is so very expensive. Why is that?

As Congress argues over the size of the infrastructure bill and how to pay for it, very little attention is being devoted to one of the most perplexing problems: Why does it cost so much more to build transportation networks in the US than in the rest of the world? In an interview in early June, Transportation Secretary Pete Buttigieg acknowledged the problem, but he offered no solutions except the need to study it further.

Biden’s original infrastructure proposal included $621 billion for roads, rail, and bridges. His plan is billed not only as an infrastructure plan but one that would help respond to the climate crisis. A big part of that is making it easier for more Americans to travel by mass transit. The Biden plan noted that “America lags its peers — including Canada, the U.K., and Australia — in the on-time and on-budget delivery of infrastructure,” but that understates the problem.

Not only are these projects inordinately expensive, states and localities are not even attempting to build particularly ambitious projects. The US is the sixth-most expensive country in the world to build rapid-rail transit infrastructure like the New York City Subway, the Washington Metro, or the Chicago “L.” And that’s with the nation often avoiding tunneling projects, which are often the most complicated and expensive parts of any new metro line. According to the Transit Costs Project, the five countries with higher costs than the US “are building projects that are more than 80 percent tunneled … [whereas in the US] only 37 percent of the total track length is tunneled.”

America’s infrastructure cost problem isn’t just confined to transit, it’s also the country’s highways. Research by New York Federal Reserve Bank and Brown University researchers reveals that the cost to construct a “lane mile of interstate increased five-fold” between 1990 and 2008. New construction — widening and building interchanges and building new sections of road altogether — is where the bulk of the problem lies, says one of the researchers, economist Matthew Turner. (The cost of “heavy maintenance” like resurfacing increased as well, but Turner said that’s due almost entirely to the rise in the price of certain paving materials.) 

According to a report by the Brookings Metropolitan Policy Program, the nation’s transit spending “fell by $9.9 billion in inflation-adjusted terms” over the last 10 years. In comparison with similar countries, America spends a relatively small amount of its GDP (1.5 percent) on public infrastructure, while the UK spends 2 percent, France 2.4 percent, and Australia 3.5 percent.

The problem is fundamentally that the US is getting very little for what it builds

Infrastructure: “Why does it cost so much to build things in America?”- this is why the U.S. can’t have nice things. From @JerusalemDemsas in @voxdotcom. Eminently worth reading in full.

Chanda Kochhar

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As we lay the foundation, we might recall that it was on this date in 1886– the anniversary of the date in 1864 the Abraham Lincoln set aside Yosemite Valley as a preserve— that Congress recognized and established by law (24 Stat. L.103), the Division of Forestry in the Department of Agriculture.  Created in 1881 by fiat of the then-Commissioner of Agriculture, it’s initial remit was to assess the quality and conditions of forests in the United States.  In 1891, its mandate was expanded to include authorization to withdraw land from the public domain as “forest reserves,” to be managed by the Department of the Interior– the precursor to America’s National Forest and National Park program.

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“How many things have been denied one day, only to become realities the next!”*…

Electricity grids, the internet, and interstate highways are enormous in scale, yet we take them for granted

In 1603, a Jesuit priest invented a machine for lifting the entire planet with only ropes and gears.

Christoph Grienberger oversaw all mathematical works written by Jesuit authors, a role akin to an editor at a modern scientific journal. He was modest and productive, and could not resist solving problems. He reasoned that since a 1:10 gear could allow one person to lift 10 times as much as one unassisted, if one had 24 gears linked to a treadmill then one could lift the Earth… very slowly.

Like any modern academic who prizes theory above practice, he left out the pesky details: “I will not weave those ropes, or prescribe the material for the wheels or the place from which the machine shall be suspended: as these are other matters I leave them for others to find.”

You can see what Grienberger’s theoretical device looked like here.

For as long as we have had mathematics, forward-thinking scholars like Grienberger have tried to imagine the far limits of engineering, even if the technology of the time was lacking. Over the centuries, they have dreamt of machines to lift the world, transform the surface of the Earth, or even reorganise the Universe. Such “megascale engineering”  – sometimes called macro-engineering – deals with ambitious projects that would reshape the planet or construct objects the size of worlds. What can these megascale dreams of the future tell us about human ingenuity and imagination?

What are the biggest, boldest things that humanity could engineer? From planet lifters to space cannons, Anders Sandberg (@anderssandberg) explores some of history’s most ambitious visions – and why they’re not as ‘impossible’ as they seem: “The ‘megascale’ structures that humans could one day build.”

* Jules Verne (imagineer of many megascale projects)

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As we think big, we might send very carefully measured birthday greetings to (the other noteworthy) John Locke; he was born on this date in 1792. A geologist, surveyor, and scientist, he invented tools for surveyors, including a surveyor’s compass, a collimating level (Locke’s Hand Level), and a gravity escapement for regulator clocks. The electro-chronograph he constructed (1844-48) for the United States Coast Survey was installed in the Naval Observatory, in Washington, in 1848. It improved determination of longitudes, as it was able to make a printed record on a time scale of an event to within one one-hundredth of a second. When connected via the nation’s telegraph system, astronomers could record the time of events they observed from elsewhere in the country, by the pressing a telegraph key. Congress awarded him $10,000 for his inventions in 1849.

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