A way to Sustainable Architecture by new technologies for engineered timber structures

Julius NATTERER
* Professor hon. EPFL

Swiss Federal Institute of Technology Lausanne, Switzerland

 

ABSTRACT

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

1. INTRODUCTION

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).

Figure 1. System effect

Figure 2. Variant of cross-section

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.

Figure 3. Comparison of live and dead load

Figure 4. Principle of liaison between wood and concrete


Tower,

Lausanne (CH) 2003

Tower high 36 m. Observation platform at 30 m. Diameter: 12 m at base, 6m at the platform. 24 poles half round are distributed around the spiral staircase made of 20x40 cm Douglas sections. The spiral builds two independent staircases one behind the other. The upper platform and the two intermediates one are made of nailed laminated timber


Houses of Residence, Arlesheim (CH), 1999

The grouped residence consists of 72 two-story houses. The floor is built from VNP elements. The double diaphragm separates and stabilizes as a solid element between two houses. A layer of plaster panel also covers the visible facets for satisfying fire resistance criteria. Outside of the building, the VNP elements are in Douglas timber with a section of 30 mm x 30 mm which provides well the whether resistance without any chemical treatment. In order to optimize the construction cost, most of the elements are prefabricated.


Church, Schnerverdingen (D), 2000

The church consists of a free space with a height of 2-stories. The roof suspends a platform at the first floor. The casing of the building is erected by VNP element in Oak. The inside bearing structure is built by VNP elements in Pine. Two frames with longitudinal trusses and two transversal frames transmit the load from the platform and the church tower.

 

 


 

Sport hall, Haukivuori (FIN), 1999

Sports hall of 24 x 30 m. The roof is composed of VNP modules between the primary bearing system. This consists of subtensioned beams with a Kerto web. The walls are also made of nailed planks recovered with plywood for stabilization. Due to its easy construction system, unemployed local people can be involved. Before the construction, several tests were made in order to determine the physical characteristic of the nailed planks as well as their fire resistance. Finally, before putting them in place, the primary systems were tested with a load over 50t.