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Mjøstårnet (pronounced:/mæo-stâr-nɛt/) is the tallest timber building in the world. It is a big step towards the adoption of green construction as it portrays timber as an exceptional replacement for bricks and cement.
Mjøstårnet is 84.5 m tall and stands on the banks of the Mjøsa Lake in Norway. The 18-story mixed-use building features apartments, offices, a hotel, and a restaurant.
It is the brainchild of Arthur Buchardt and was conceptualized in 2017. The construction was completed within two years and the building has been open for the public since 2019.
1. Why Timber as a Building Material?
Timber, in its natural state, is not suitable as a construction material. It tends to retain moisture, is prone to insect attacks, and does not possess the structural strength to support a building half as tall as the Mjøstårnet.
Despite the above-mentioned properties, it has been used successfully in the construction of buildings like Treet and Mjøstårnet. This is because of the characteristics of engineered timber, such as lesser emissions, renewability, efficiency, and aesthetics.
2. Construction Details of Mjøstårnet
Presently, the highest occupied floor height of the building is 68.2 m. The architectural top height is 85.4 m, and height to tip, 88.8 m.
The construction of Mjøstårnet involved the assembly of four stories at a time, with five construction stages. It was built without an external scaffolding and required just a large crane and internal scaffolding combined with lifts.
The structure formed with engineered timber was first assembled on the area next to the site and hoisted up. Thereafter, the floor slabs were hoisted into place.
3. Types of Engineered Timber used in Mjøstårnet
Mjøstårnet is built with three types of engineered wood: Glulam, Cross-Laminated Timber (CLT), and Laminated Veneer Lumber (LVL).
Mjøstårnet is an assembly of seven hundred large members of Glulam, which is an integral part of the building's timber construction. Glulam is a composite block of several planks of wood glued together in parallel. The individual pieces of wood are first chipped off for uniformity and smoothness. Then, using industrial adhesives, the pieces are stuck together to form one strong block. This robust block of wood is known as Glulam.
3.2 Cross-Laminated Timber
The production of CLT is similar to that of Glulam, the only difference being the orientation of the individual wooden planks. Unlike Glulam, the pieces are placed perpendicular to each other in the case of CLT.
CLT members are capable of providing the same structural strength as their concrete counterparts. Furthermore, they also provide flexibility to the structure. They are widely used in the construction of stairs, balconies, and lifts.
3.3 Laminated Veneer Lumber
A veneer is a thin piece of wood, and multiple layers of such veneers make up LVL. The veneer has a thickness of around 3 mm and is a lot thinner in comparison to Glulam. After the layers attain suitable moisture content, they undergo lamination. They are then given an even coating of industrial adhesive, after which they undergo continuous heating. The final product is then cut into different shapes and sizes.
Although LVL offers advantages like customization and fire resistance, it is not as reliable as CLT and Glulam. It requires constant on-site inspection during storage as well as post-construction due to its moisture susceptibility.
Timber elements, such as the Glulam beams and columns, make up the floor slabs of the first ten levels of the building. The rest of the floors, featuring only residential apartments, have concrete decks.
Timber is not strong enough to withstand heavy winds or storms, and hence, concrete slabs are necessary in the upper floors to provide stability to the top of the building.
The Mjøstårnet deserves appreciation not only for its innovative construction but also for the facilities it offers. The building is one of the most unconventional and sought after tourist spots in the world. Not only is it an example of a greener approach towards construction, but also a true engineering marvel.
As evident in the case of Mjøstårnet, people have been happily residing in the building. It breaks all the myths of timber buildings being unsafe in case of fire breakouts or other calamities.
Besides controlling the carbon footprint, timber houses are acoustically and aesthetically appealing too. And above all, these buildings are no less than the conventional ones in terms of strength and durability.
Timber construction also has a few limitations. First, production of engineered timber is usually much more expensive than cement or brick production. Second, timber tends to retain moisture if not treated properly.
Third, timber structures can easily lose their sheen. Also, they require vigilance while in the storage. However, the disadvantages of timber are easily outnumbered by its advantages. This is why timber construction is very popular these days.
A Glulam beam can easily achieve the strength equivalent to that of a steel one. For instance, a wide flange steel beam, W 6x9 (depth= 6 inches and linear density = 9 lbs/ft) is replaceable by Glulam beam of dimensions 5.13x11 inches (depth= 5.13 inches and linear density=11 lbs/ft) as a roof beam.
Hence, it is not correct to declare either of them structurally stronger. However, Glulam is much more environmentally friendly and fire-resistant than steel.
- Different Types of Industrial Timber - Uses and Properties
- Why is Timber Construction Popular in 21st Century?