Engineered Timber Materials Essay Example
- Category:Engineering and Construction
- Document type:Assignment
7Engineered timber materials
Engineered Timber Materials
Engineered Timber Materials
Timber is an incredibly rapidly growing, affordable and widely available natural resource which has outstanding constructive qualities. The cultivation and industrially processing of timber offers huge potential in the form of composite material products such as plywood, Medium Density Fibreboard (MDF) and cross laminated timber. The research paper is investigating these engineered timber products. This paper documents the investigations that were carried out in order to understand the engineered timber products also known as man-made timber products in accordance to its change of mechanical and physical properties. All products are addressed in this paper. Therefore, no specific statement is provided in this paper regarding the varying qualities and properties of different timber sections and layers.
Wood is the oldest and the most widely used building material. It can be found almost everywhere in the world, and its characteristics make it suitable to be used in a broad range of applications. One of the aspects of wood is that it is in the category of renewable resource: if the wood resource comes from sustainably managed forests, it will be available indefinitely. As we engage with a sustainable agenda, it seems appropriate to carefully evaluate a construction material whose environmental benefits are matched by few others. This report provides a review on the whole range of derivative timber products, to which we can inclusively refer to as ‘engineered timber’, with regards to their sustainability potential. After an overview of the engineered timber products and their general characteristics, the report focuses on how those products behave environmentally, according to their degree of technology and processing from the original material wood. An overview of the products’ assessment and application in sustainable construction is presented. In the last section, some observations on the role of timber in contemporary architecture, more specifically on how engineered timber applies to modern methods of construction and reusable/adaptable structures, are followed by two case studies that are representative of the novelty of application.
Engineered timber materials
The development of engineered timber has been historically related to economic advantages. Investigation and research on ways and means of using the wood more efficiently has generally been considered to be driven by the increasing cost of sawn timber and green logs. Despite constantly increasing their efficiency, sawmills still produce considerable amounts of residues in forms of low grade logs or thinnings, chips, slabs and sawdust; those can be used to manufacture many kinds of wood-based panels. While that is certainly true, it would be it quite reductive to consider the technological progresses on timber solely in terms of economic savings. To respond to a need of diverse applicability and improved performance, the construction industry has identified manifold technical reasons to guide the application of engineering processes onto sawn timber and overcome its shortcomings.
Top, branches and foliage
Slabs, edgings and off-cuts
Structural Timber Composites
Structural Timber Composites
Cross Laminated Timber
Solid wood panel
Fiber board (MDF)
Oriented Strand Board (OSB)
Laminated Strand Lumber (LSL)
Wood particleboard (or chipboard)
Double laminated beams (Duobeams)
They have of two timber lamellae, rigidly stacked together after visual or machine strength grading. After being glued, they are opposite combined and chamfered on four sides. Each lamellae has to be finger-jointed.
Glued timber is manufactured from laminates of sawn wood, dried kiln and glued together with parallel fiber alignment. The process of jointing allows all laminates to be end to end jointed to produce better lengths. High resistance and dimensional stability properties make glulam particularly suitable for elements bearing high stresses or spanning large distances. The choice of the adhesive has to be accurate in order to fulfil the European standard requirements for loadbearing timber components.
It is manufactured from 3 mm thick and 15 mm wide strips of veneer, bond together with phenolic resin. The strips are bundled with fibres oriented primarily parallel to the major axis of the beam. They are processed in a continuous press to form an endless beam. Parallel strand lumber is designed to be used in structures with long free spans. PSL elements can be bonded together, to obtain components with large cross-sections.
Solid wood panel
It is a multi-layered board, with a symmetric lay-up consisting of parallel outer layers and at least one core layer, oriented perpendicularly to them. The individual lamellae are sorted, planed prior to their assembly into the boards, thus minimizing swelling and shrinkage due to climatic changes
Veneer lumber is manufactured in a continuous process that consists in bonding individual spruce or pine veneers with their own ends back and with fibers generally in one direction. PF resins are generally used as adhesives. Veneer lumber finds application as bracing element in load bearing ceilings and floors, and can be used in the same applications as glulam.
Plywood is a panel composed of a joined of layers packed together, usually odd in number (3, 5 or 7) and not exceeding 7 mm in thickness. Each veneer is put down with its own grain at 90 degrees angles to the adjacent layer, and all the veneers are aligned with their parallel plane to the top of the plywood panel. Veneer Plywood are always very delicate product: it offers high weight to strength properties and it performs well under severe exposure conditions; the choice of the adhesives for its manufacturing determines the panels’ suitability for internal or external use.
Different types of veneer plywood are mostly available in the world: structural plywood, utility plywood and decorative plywood.
Production varies depending on several factors, but it usually includes the following sequence of processes:
Jointing or veneer repair
Trimming, filling and sanding
Medium density fiberboard (MDF)
In Medium density fiberboard the fibers of cellulosic material are combined together with both the basic bond usually derived from a combining agent. The properties of the material can be modified or enhanced by interchanging the type of the synthetic combiner or by incorporation of other elements during or after manufacture.
Medium density fiberboard is the most common dry process board. The specific machining and completing attributes, joined with better working situations and a variety range of necessary sheet length and sizes allow Medium density fiberboard to find multiple applications in construction, e.g. skirtings, architraves, window boards, wall linings and decorative facades. It includes:
Waferising, strand cutting and drying
Trimming, conditioning and sanding
Sustainability credentials of engineered timber products
As discussed earlier, the most important mechanical properties of the engineered timber composite material have been investigated. Research show that the tensile strength of engineered timber composite material is as high as the engineered timber fibers used to produce it. Knowing that engineered timber has tensile strength of 400 MPa without nodes, the tensile strength of 500 MPa for the given engineered timber composite material including nodes is significant. Not only the tensile strength but also the flexural strength as well as compressive strength of the engineered timber composite material are considerable. Engineered timber composite material has a unique behavior in compression and bending which shows the ability of the material to absorb more energy before it fails.
It is known that different species of tree have different mechanical properties, so by using a stronger tree species, one can optimize, for example, the tensile strength capacity. Different agents will have different effects on the mechanical properties of engineered timber materials, including water absorption and thermal expansion. By using a high tensile strength fiber to produce the engineered timber composite material, the final tensile strength would be significant when compared to steel and concrete. After understanding and manipulating the material properties of fibers, the effect of engineered timber composite material on concrete matrix is high. Besides the mechanical tests such as flexural or tensile strength tests, investigating the bonding between the new material and concrete matrix is of significant interest especially relating to long-term durability, water resistance, thermal expansion, swelling and shrinkage. By controlling the moisture content in engineered timber composite material and with the help of specially designated adhesive agents, the usual problem of swelling and shrinkage in raw timber will be controlled. Raw timber is highly susceptible to attack by staining fungi and powder-post beetles as well as white and brown rots. This low natural durability leads to the gradual degradation of raw timber, which in return results in loss of its strength and load bearing capacity. The described engineered timber composite material will resist such attacks. The interaction between concrete matrix and engineered timber composite material as well as the chemical reaction between concrete curing products and chemical admixtures used in concrete are of high importance. Accelerators, retarders or even plasticizers that are commonly used in concrete to give the mixture certain properties have different impacts on an engineered timber composite material. In developing the described engineered timber composite material, those effects require further investigation and certain chemical tests need to be developed. For instance, the effects of “Cl” ion on engineered timber composite material are certainly important especially in long-term durability of the reinforced concrete.
Cross-laminated timber panel school, Open Academy, Norwich
The school is the currently the largest solid wood building in the Norwich city. Crucial for the contractor’s bidding success were the key advantages offered by massive timber construction: sensible savings in construction time and major environmental benefits. Thanks to its versatile structural capabilities, Cross Laminated Timber applied really well to most significant features of the design:
Atrium roof: cross laminated panels, acting as a rigid horizontal diaphragm; they are supported by 12 glulam arches.
curved walls: facetted cross laminated panels, provided in 2.4m lengths;
cantilevered stairs: exposed timber treads underneath and exposed timber walls;
Cross Laminated Timber presented higher initial costs but subsequent valuable economies, such as a shorter programme, pre-cut openings, made off-site and ready to host windows and doors without additional framing, simplified fixing for services, no need of scaffolding and finally reduced risks for the workforce.
With regards to the environmental impact, as illustrated in the previous chapters, massive timber has the lowest embodied energy of any building material. The carbon footprint of the Open Academy has been calculated to be approximately half that of an analogous steel or concrete structure. Thanks to the additional estimated 3000t of CO2 sequestration, the building results to have a ‘negative’ carbon footprint.
The chosen environmental strategies of passive solar design and natural ventilation required high performance for the building fabric and reduction of heating, cooling and artificial lighting demands. Cross laminated panels guaranteed air tightness of less than 5 m3/hm2, half of the building regulations requirement.
BRE Innovation Park, 2007
Constructed in the BRE Innovation Park in Watford, this ‘mini’ school embeds sustainability as a core element of its curriculum.
It aimed to be demonstrative of all the building principles that shall guide the schools of the future; as a result, every part of the design, construction and operation was looked at as an educational opportunity.
The school was conceived to showcase the potential of modern methods of constructions to be sustainable, low operational and embodied energy, cost effective and aesthetically valuable.
Designed to be relocated, the school is built in Solid Wood Panels (SWP) manufactured off-site from recycled off-cuts and then assembled on site through screwed butt joints. The timber structure lies on a steel frame with screw piles foundations, which facilitate removal prior to relocation. The building in Watford has two and a half storeys, but the solid timber systems could potentially go up to ten.
Post-completion tests demonstrated that, thanks to the state of the art cutting and joining of the panels, the structure achieved a high level of air tightness, delivered the desired acoustic performance and benefitted from excellent thermal behaviour of the solid wood panels.
Hairstans, R., 2010. Off-site and Modern Methods of Timber Construction: A Sustainable Approach, TRADA Technology Ltd.
Hartwig, J., Zeumer, M. & Viola, J., 2009. Sustainable use of materials: wood and wood-based products. DETAIL Green, (2/2009), pp.56-59.
Kretschmann, D.E., 2010. Mechanical Properties of Wood. In Forest Products Laboratory, ed. Wood Handbook. Wood as an Engineering Material. Madison, WI: US Department of Agriculture Forest Service, Forest Products Laboratory, pp. 100-145.
Stark, N., Cai, Z. & Carll, C., 2010. Wood-Based Composite Materials. In Forest Products Laboratory, ed. Wood Handbook. Wood as an Engineering Material. Madison, WI: US Department of Agriculture Forest Service, Forest Products Laboratory, pp. 252-279.
Thun, M., 2010. Wood in Architecture, Interior and — Product Design – a Homage to a Building Material. DETAIL, (06/2010), pp.552-670.
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