A way to Sustainable Architecture by new technologies for engineered timber structures
Swiss Federal Institute of Technology Lausanne, Switzerland
Only the use of wood in the construction field can save and renew the forests of the world and motivate people to maintain and plant forests in a sustainable way.
Today, ecological concerns become more and more important and wood, under the double aspect of the energy necessary to its production and its aptitude to store CO2, could be the best-suited building material of XX1e century. However, if these ecological concerns take more amplitude and influence, there is another aspect, the economic concern. Thus each project must present not only one ecological or architectural value, but also an economical one.
Keywords: massive wood, nailed planks, mixed structures, glued and spatial structures
Today, ecological concerns become more and more important and wood, under the double aspect of the energy necessary to its production and its aptitude to store CO2, could be the best-suited building materials of XX1e century. However, if these ecological concerns take more amplitude and influence, there is another aspect, the economic concern. Thus each project must present not only one ecological or architectural value, but also an economical one.
It is necessary to promote the different possibilities where wood as timber can be used. Besides the utilization of high quality wood for high-tech constructions of halls, wide span covers and bridges, one should further develop the possibilities of using medium to low quality for massive-timber construction for floors, walls and roofs, also in association with other materials like steel, concrete, glass or fiber glass.
2. Massive-timber constructions
Round, sawn timber constructions or nailed, screwed, doweled and glued massive plank systems today allow us to reach these objectives. The nailed, screwed, doweled and glued massive plank system consists of planks, aligned one next to the other, face to face and assembled with nails. Massif elements with a thickness that corresponds to the width of the planks are obtained. With these systems, a hypothetical defect in one plank will not lead to a failure of the whole structure. The stress is then taken over by the adjacent planks through the nailing pattern (fig. 1).
The advantages of these structures are multiple. They allow reducing the necessary static height in comparison to the traditional joist and improve the acoustic protection as well as the thermal inertia. With this system, during summer, overheating of the buildings is limited and in winter, the solar heating is better distributed during the day. These structures may remain visible, coated or not, or recovered with plaster and wall paper. Different variants of sections can be obtained without high costs (fig.2).
For floors, higher spans can be obtained through the use of mixed systems, where wood is in tension and concrete in compression. Materials are thus used to their best abilities. The connection between the two components is realized through grooves and pre-stressed bolts (fig. 4). Depending on the different loadings and the aesthetic requirements, the wood parts can have differing forms: From round wood for bridges or half-round wood for ceilings without any particular aesthetic demands, to nailed planks for normal buildings or even glue laminated beams in “T” section for high stressed floors. Comparing to a traditional concrete slab, the self-weight is heavily reduced (fig.3) and it is fire resistant from 60 to 90 min.