With an expected completion date of March 2019, the 18-story, 80-meter-tall-plus building in Brumunddal, Norway known as the Mjøsa Tower will soon become the world's tallest wooden structure, a coveted title among those designers who favor wood over more traditional tall building materials. Designed by Voll Arkitekter, the Mjøsa Tower is on track to supersede the previous wooden record holder, the Brock Commons Student Housing building at the University of British Columbia, which topped out at a stately 53 meters in height.
Wood has numerous advantages over oft-used concrete and steel: for one, the construction time can be cut approximately in half due to easy prefabrication and the overall lighter weight of the materials. Surprisingly, one of wood's advantages as a tall building material lies in its ability to withstand fires, at least when compared with the tendency of steel to melt down during an all-consuming blaze. As the site's general contractor Erik Tveit, who is also the Project Manager at HENT AS explains, "Fire safety rules state that buildings must be able to withstand a full fire for at least two hours without collapsing. When you have a building made of steel and concrete, the steel melts and the building collapses."
The tower's attributes aren't limited to its choice of building material. With a site that borders a river, Øystein Elgsaas from Voll Arkitekter explains that "The facades of Mjøstårnet will be dressed in wood panels in a stylized and repeating pattern inspired by the movement of the water and the way light dances on the ripples of its surface.”
However, it's worth noting that this building is not made entirely of wood: in order to keep the tower from swaying in the wind, concrete will be added to the upper storeys to act as a stabilizer. The contractors are careful to note that, "Nevertheless, concrete will be used between the floors of the Tower’s top seven storeys. Using concrete has nothing to do with the load-bearing capacity. There's a simpler explanation: the swaying that increases the higher you get in a building built of wood or concrete. The weight of the concrete in the upper storeys makes the swaying slower and not as readily perceivable."
Norway already has the world's tallest timber building, Treet in Bergen which has a timber core and also uses concrete floor plates at intervals to stabilise. Including Brock Commons and similar schemes in a height comparison between timber buildings is pretty useless because these are in fact hybrid structures relying on their concrete core.
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Concrete would be superior in its performance vs. wood. I think what the author should focus on the installation of a sprinkler system which is the savior of all these buildings. Maybe not as good as concrete, but acceptable and ethical when looking at the environmental impact of concrete vs wood. My question to any gurus out there in the industry is what is holding back mass timber framing? Why is it so expensive? Why do we not talk about the rotting and moisture issues with wood?
"one of wood's advantages as a tall building material lies in its ability to withstand fires, at least when compared with the tendency of steel to melt down during an all-consuming blaze."
In the most recent high-rise steel-structure building fire in the U/K the steel did not melt down. Nor has it ever that I am aware of.
Steel loses structural integrity with increased temperature and goes plastic long before melting. Building fire temperatures are typically well in excess of those necessary to reach this point.
Arlington Park, NJ
Going back to wood-frame construction, this is why gang-nail trusses are deadly. The steel truss plates fail suddenly as soon as they reach critical temperature. The wood elements - even 2x4's - take a few minutes to burn through.
"The weight of the concrete in the upper storeys makes the swaying slower and not as readily perceivable"
I hope you're talking only about a diaphragm slab vs wood beam/joists, because putting more weight on the top increases the swaying of the whole in a seismic event or wind load increase.
Norway already has the world's tallest timber building, Treet in Bergen which has a timber core and also uses concrete floor plates at intervals to stabilise. Including Brock Commons and similar schemes in a height comparison between timber buildings is pretty useless because these are in fact hybrid structures relying on their concrete core.
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