chrispy thoughts

-the world as I see it

Wood you bet high on it?

Hello readers, this post is a tad bit technical and might not be of much interest to non-civil engineering folk. There, I have warned you in advance.

Wood is one of those materials that invokes starkly different reactions to its usage in construction by architects and engineers. While the former welcome it for its aesthetic appeal and design possibilities, the latter frown upon it with uncertainty regarding its performance under fire and wind and added concerns on stability and durability. Although many countries have had a history of building tall with timber, the advent of concrete and steel at the turn of the last century, almost entirely displaced the use of timber in multi-storeyed structures.

In the wake of issues like climate change and global warming, there is an urgent need for limiting greenhouse gas emissions and reducing the carbon footprint. As the building industry uses a sizeable chunk of the earth’s resources and is one of the major pollutant sources, it is the prerogative of this industry to come up with eco-friendly building solutions.You’re probably wondering how timber construction can even be considered a potential solution to the problem, when it could lead to a scenario of deforestation. Research in sustainable forest management has revealed that it is beneficial to regularly harvest wood rather than to allow trees to grow for hundreds of years. So when wood comes from well-managed forests, it is, by far, the environmental building material of choice. The development of engineered wood products and improved techniques of construction along with the shift to performance based design has created a renewed interest in timber construction systems, particularly in medium- and high-rises.

Currently, the most- researched engineered wood product is  Cross Laminated Timber (CLT). Conceived in Switzerland in the 1990s and further developed on an industrial scale in Austria and Germany in the 2000s. Construction with cross-laminated timber is fast and cuts costs, which is one of the main reasons of CLT gaining a foothold in the competitive building industry.

WHAT on earth IS CLT ???

In layman’s terms, CLT panels are nothing but symmetric timber sandwiches where the bread as well as the filling is made of timber. The timber filling is arranged perpendicular to the outer-most timber layers. These ‘sandwich layers’ are glued and pressed together, after which they are planed and sanded in factories so that they are firmly held in conjunction. The number of layers usually varies from 3 to 7. You can see what the cross section of a CLT panel looks like in the picture below.

CLT

Structures made of CLT are way stronger than normal timber structures because of the bi-directional increase in load carrying capacity. The construction technology can be considered as a sort of an innovation based on tradition – combining the use of the vertical bar-like behaviour of timber in frame construction and the horizontal bar-like behaviour in log houses, which are both traditional forms of timber construction.

CLT Load resisting mechanism

+1s

  • With simple construction techniques and a high extent of prefabrication, modern timber structures can be built in a relatively short span of time, ranging from a few days to a few weeks.
  • Since CLT structures weigh less than concrete or steel, the foundation requirements are less and this reduces the cost.
  • Good seismic resistance
  • Excellent thermal performance
  • Fire resistance? Not to worry, these structures deliver on that aspect as well. The ample cross-section of the panels ensures that in the event of a fire, there is a thick enough unaffected layer beyond the charred portion to ensure the integrity of the building remains unaffected.

EMBRACING CLT

After gaining popularity in Europe, this engineered wood product has made its entry into the construction industry in the U.S, Canada, Australia and New Zealand.

Since the L’Aquila earthquake in 2009, the use of timber as a structural building material has soared in Italy. The extensive damage suffered by the concrete buildings has made the building industry focus on building with wood and exploring the area of multi-storey timber constructions. CLT is being considered as a preferred choice for the rebuilding process.

Taking pointers from Italy, research efforts to develop modern timber construction systems have gained momentum in New Zealand after the Christchurch earthquake in 2011. While previously, the city consisted of predominantly masonry buildings, their poor performance during the earthquake combined with the vision of rebuilding Christchurch as a green city, has seen timber playing an important role in the rebuilding process. The pine trees in New Zealand are well suited for high value prefabricated building components and wall and ceiling linings. Since they are available locally, it eliminates the need for importing raw materials and hence reduces costs.  Many of the proposed building solutions will be built using CLT.

In North America, where several pine trees in forests have been affected by beetle infestation, converting the wood into CLT would be very beneficial.

AND THE MEGALOMANIA HAS SET IN

In a bid to secure the ‘I have the tallest timber building’ title, a number of countries are designing high-rise CLT structures. At present, Australia leads the race with Forte, a residential apartment in Melbourne standing tall at 32.17 metres.  Let us take a look at how its European competitors are faring.

clt Europe

As of now, CLT hasn’t  made an entry into the building industry in tropical and sub-tropical countries. But it probably won’t be too long before significant improvements in the durability will ensure their feasibility in these regions as well.

Since there are no building codes in place for CLT structures, there are restrictions and reservations on how high one can build with this material. But with the way things are shaping up, ‘plyscrapers’ might just dominate the skyline of the future.

READ THIS…

http://techniker.oi-dev.org/assets/264739566/52/Tall%20Timber%20Buildings%20Feb10.pdf

http://www.masstimber.com/building-types

…..WATCH THAT

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3 comments on “Wood you bet high on it?

  1. Neeraj
    February 12, 2014

    Never thought wood would (:-P) ever be considered for structural construction in the future!! Interesting C!!:-)

    • C.
      February 12, 2014

      Yeah, very interesting 🙂
      In India we hardly even learn about timber because the code doesn’t allow you to build higher than 2 storeys with wood.

      • Neeraj
        February 12, 2014

        Hmm..achha

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This entry was posted on February 12, 2014 by in Civil Engineering, Environment and tagged , , , , , , , .

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