Panel construction

Current developments

Fig. 37: Wood welding

The application of ultrasonic energy causes the plastic to form a connection with the wood at the macroporous level.

Fig. 37: Wood welding

The application of ultrasonic energy causes the plastic to form a connection with the wood at the macroporous level.

The structural system of panel construction is determined by loadbearing slabs or panels, which are joined in a "slab tectonics" system to form a stable assembly. This distinguishes them from those sandwich constructions which, although prefabricated to form internally lined and externally clad frame constructions, still consist of linear members (the so-called black box). The planar nature of the isotopic loadbearing panel leads to completely new structural and design-related properties unusual in timber engineering. The grid of regularly spaced loadbearing elements so typical of traditional timber building is now superfluous, and openings can be cut almost anywhere in the surface.

Material conglomerates

Recent trends in the construction industry have led to changes in the design and building processes and hence the role of the architect. The diversity of the systems and materials on the market mean that the architect is increasingly reliant on the specific expertise of industry, which can offer ever more comprehensive end-to-end solutions and is therefore focusing the specialist knowledge and guarantee clauses on the side of the manufacturer.

Looking at solid construction it would seem that all innovations are concentrating exclusively on new cladding systems or surface finishes. The structural shell has hardly changed, hardly developed any further. In situ construction continues to prevail in Central Europe, despite the relatively high cost of labour and, sometimes, obvious deficiencies in the workflow. We could take electricians as an example: no sooner is the masonry wall built, do they begin to cut slots all over it for their cables and conduits! Multi-layer building component systems - hardly ever developed by the architect any more, but instead merely chosen out of a catalogue - clad our conventional structural shell something like a "camouflage strategy".

Looking at timber construction we find that current developments and innovations are of a more fundamental nature. In this respect the timber building sector has assumed a special status within the construction industry. Here again, however, high-tech skills are being delegated to the specialists employed by the manufacturers. This eases the architect's workload because he or she no longer has to consider the detailed inner workings of the construction. On the other hand, this competence is being lost from the architect's range of skills.

Semi-finished products and the manufacture of wood-based products

In Central Europe and Scandinavia the movement in this sector was triggered by a crisis in the timber building industry. In order to regain market share from solid construction and to find a rapid use for wood from trees brought down in severe storms ("Vivian" in 1990 and "Lothar" in 1999) innovations were urgently required.

Such innovations initially focused on semi-finished goods and the manufacture of wood-based products. Traditional woodworking processes require timber cross-sections with a roughly consistent quality. This means that when cutting planks, squared sections and boards only healthy, straight trunks can be used and therefore offcuts and side boards of lower quality abound. Nowadays, these sections are used, cut down into smaller strips, battens and laminations. Chips and sawdust represent the end of this processing chain.

The process of breaking down into ever smaller parts is accompanied by a contrary process - assembly. The smaller the constituents in the assembled products, the more homogeneous are their physical properties and the easier it is to influence these properties through the type of assembly and the choice of chemical or mechanical binders. When using chips or sawdust, synthetic materials such as adhesive or cement are used, depending on the intended application. Semi-finished products made from strips or laminations are usually glued together, which increases their structural usefulness and opens up new options for construction.

The search for suitable connecting options and their ratio to the proportion of wood paves the way for semi-finished products in which the boundary between wood-based products and other materials, e.g. plastics, becomes vague as we try to achieve optimum properties. This is true of the current trials surrounding new connections, e.g. wood welding, where thermoplastic connecting materials are vibrated by ultrasonic energy and thus flow into the porous structure of the wood. Wood welding results in a stable connection that can be loaded immediately.

These developments in materials form the basis for new types of timber construction. The considerably more consistent physical properties (compared with natural wood), which are reaching hitherto unknown proportions, depending on the particular range of products, render new applications in timber engineering possible. It is therefore only a matter of time before the first timber building systems with completely new structural and building performance properties appear on the market.

Custom prefabrication

The shift from production on site to production in the factory, where thanks to controlled conditions and workflows it is possible to achieve greater accuracy, enables timber building contractors to keep control of the majority of the production process. Almost all current timber building systems are flexible enough to be able to react to individual designs. Trying to keep the design within a module suitable for timber engineering is now a thing of the past. Only the maximum spans possible still influence the plan layout. The traditional design process for a timber building constructed by carpenters has therefore been reversed:

Fig. 38: The ribbed solid timber panel as an example of a black box system

Finished sandwich elements are delivered to site with their internal structure no longer visible

Blackbox

Fig. 38: The ribbed solid timber panel as an example of a black box system

Finished sandwich elements are delivered to site with their internal structure no longer visible the structure can be designed with a relatively high degree of freedom in order to be broken down into suitable individual parts or elements in the next stage of the design (custom prefabrication). At best, only transport restrictions impose limits here.

Black box systems or sandwich systems

Today, it is possible to request quotations from suppliers of different systems based on tender drawings at a scale of 1:200. The days in which the architect drew the entire loadbearing timber construction in great detail are now over. This work is carried out by the system supplier awarded the contract, who is also responsible for detailed design of the system and compliance with the building performance criteria. The details specific to the project are solved in cooperation with the architect, possibly with repercussions for the loadbearing system. The closed black box elements - fulfilling all requirements - are delivered to the building site and erected, an inner lining and/or external cladding being added if required, depending on the system. (The term "black box" is not specific to any form of construction and can be applied to panel construction or platform frame elements.)

Panels indifferent to the direction of span

One characteristic that determines the design in panel construction is whether the direction of the panels is relevant or irrelevant. Panels in which this aspect is irrelevant are those made from wood-based products whose structure within the plane of the panel is isotropic. As wood naturally has a directional - anisotropic - character, this distinction has only become possible thanks to progress in the manufacture of semi-finished and wood-based products, e.g. cross-banded plies of veneers or strips. Such panels exhibit high strength and rigidity. They achieve plate effects and can be assembled and cut almost like in modelmaking. This can be seen, for example, in the treatment of openings, which can be seemingly cut anywhere and do not even require a l intel, provided there is enough material above the opening.

Timber construction systems

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