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  • Towering 85 meters above the Norwegian countryside,

  • Mjøstårnet cuts a sleek shape in the rural skyline.

  • Housing 18 stories of restaurants, apartments, and hotel rooms,

  • this modern building might seem out of place.

  • But a deeper look reveals it actually blends in quite well

  • among the forested farmlands.

  • This is likely because Mjøstårnet is the world's tallest wooden building,

  • made almost entirely from the trees of neighboring forests.

  • Until the end of the 20th century,

  • engineers thought it was impossible to build

  • a wooden building over six stories tall.

  • Traditional boards of lumber were fairly strong against forces

  • parallel to the wood's fiber growth.

  • But they were vulnerable to forces applied perpendicular to this direction.

  • As a result, wood lacked steel's tensile strength

  • or concrete's compressive strength

  • each necessary to support tall buildings

  • and battle the powerful winds found at high altitudes.

  • But the early 1890s saw the invention of glue laminated timber, or glulam.

  • And a century later, engineers developed cross-laminated timber, or CLT

  • These new wooden materials start out like all other lumber;

  • a freshly cut log is sawed into smooth uniform boards of wood.

  • Then, in the case of CLT, the boards are glued together in alternating orientations

  • with each layer set at 90 degrees to its neighbors.

  • The resulting material benefits from wood's structural rigidity

  • in every direction,

  • allowing it to mimic the compressive strength of concrete

  • and bear loads up to 20 times heavier than traditional lumber.

  • Glulam on the other hand, glues boards together in the same direction,

  • forming massive beams with tensile strength comparable to steel.

  • Glulam isn't as versatile as CLT,

  • but its incredible strength along one direction makes it superior

  • for load-bearing beams and columns.

  • These engineered forms of wood could finally compete with traditional materials

  • while also bringing their own unique set of advantages.

  • At one-fifth the weight of concrete,

  • building with CLT requires smaller cranes, smaller foundations,

  • and fewer construction workers.

  • While concrete has to undergo a time-intensive process

  • of casting and curing in a mold,

  • timber can be shaped quickly using computer directed cutting machines.

  • And where concrete requires certain weather and timing conditions

  • to be poured on site,

  • engineered wood can be prefabricated in a factory,

  • creating standardized parts with clear instructions for assembly.

  • Taken together, these materials allow for faster and quieter construction,

  • with more biodegradable materials and less waste.

  • Once constructed, CLT and glulam buildings are also more resilient

  • to some natural disasters.

  • An earthquake can crack concrete, permanently weakening an entire structure.

  • But cracked wood panels can be easily replaced.

  • The same is true for fire safety.

  • As temperatures rise in a CLT building, the material's outer layer will char,

  • insulating the inner layers for up to three hours.

  • This is more than enough time to evacuate most buildings,

  • and once the smoke has settled, charred panels can be swapped out

  • unlike melted steel beams.

  • But perhaps the biggest benefits of CLT and glulam

  • are outside the construction site.

  • Building construction is responsible for 11% of annual global carbon emissions,

  • and the production of steel, concrete, iron, and glass

  • are major contributors to that figure.

  • Timber, however, is a renewable resource that can be made carbon-neutral

  • if trees are planted to replace those cut down.

  • Wood also has low thermal conductivity,

  • making it easier to heat and cool buildings with less energy waste.

  • Despite these advantages, CLT requires vastly more lumber

  • than traditional wooden construction.

  • And when compared in similar quantities,

  • neither CLT or glulam is as strong as steel or concrete.

  • Even Mjøstårnet isn't made entirely of wood,

  • as it contains concrete slabs to reinforce the upper floors.

  • Taken together, it's unlikely that a purely wooden structure

  • would be strong enough to support a 40-story building

  • the minimum height for a formal skyscraper.

  • But even if only buildings under 30 stories were built from wood,

  • it would reduce the carbon footprint of those structures by more than 25%.

  • So no matter how tall these wooden buildings rise,

  • each one contributes to the health of our concrete jungles.

Towering 85 meters above the Norwegian countryside,

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B2 US TED-Ed concrete wood wooden lumber timber

Could we build a wooden skyscraper? - Stefan Al

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    OolongCha posted on 2021/07/09
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