Download Timber: Advantages, Disadvantages, and Processing and more Lecture notes Architecture in PDF only on Docsity! Lecture 12
Timber
Crown
branches & leaves
Trunk
Root structure
Advantages Natural products and renewable resources. Less energy required than alternative materials. No disposal problem after use. High strength weight ratio. Warm ‘feel’. Easily cut with hand tools and joined with nails or screws. Strong joints formed with adhesives. Good fire resistance for structural timber. 2 Wood Structure Hardwood Trees such as oak橡樹, 橡 木 , maple楓木& teak柚木 with broad leaves that are shed in winter. Usually grow more slowly than softwood but harder, denser, stronger and more durable. Used in window, door, high quality joinery and veneers薄板, 膠合板, 單板 for doors and furniture. 5 Wood Structure Hardwood Trees such as oak橡樹, 橡 木 , maple楓木& teak柚木 with broad leaves that are shed in winter. Usually grow more slowly than softwood but harder, denser, stronger and more durable. Used in window, door, high quality joinery and veneers薄板, 膠合板, 單板 for doors and furniture. 6 oak maple teak Wood Structure Sapwood & Heartwood Sapwood (The newly formed outer wood located just inside the vascular cambium of a tree trunk and active in the conduction of water. Sapwood is usually lighter in color than heartwood.) 7 Wood Structure Heartwood The inner layer of the tree. No longer stores food but supporting the tree. Cells is acidic for preservation of the tree. Darker in color than sapwood. More heartwood in old trees and better durability. 10 Effects of Moisture Moisture content is the mass of water contained in the wood, expressed as percentage of the mass of oven-dry wood. Moisture content = mass of water present in as sample x 100% mass of that sample when oven dry 11 Effects of Moisture Timber tends to attract water from a damp atmosphere and give up water to a dry atmosphere. Timber cells become swollen on wetting and occupying more space than dry timber. Variation of movement of timber with direction results in distortion when green timber dried. 12 Kiln Seasoning 15 Air Seasoning The timber stacked in open-sided sheds to promote drying without artificial assistance. Stacked about 450 mm clear of the ground. This process minimizes damage but this process very slow often taking several years to complete. This process cheap compare to drying kiln but will not reduce the moisture content below about 16%. 16
AIR CURRENTS
Air Seasoning
Insect Attack Insects have a characteristic life cycle: egg, larva, pupa, and finally adult insect. Insect attack does not require wet timber, though higher moisture contents are preferred. Sapwood is much more susceptible to insect attack than heartwood. Attach is less likely in wood products such as chipboard, containing synthetic adhesives. 20 Durability of Timber It refers to long term performance of the material. Wood can be durable if it well seasoned and kept in dry place, or buried in the ground. Heartwood of all species has a very good resistance. Sapwood is susceptible to decay if not used properly in construction. 21 Timber Treatment Wood need to be chemically treated because: a) To prevent destruction from fungi and insects b) To inhibit combustion This kind of treatment done by injecting chemicals under pressure into the wood fibers and is called “preservative treatment”. 22 Water-Borne Preservative Tolerant of some moisture in the timber Colourless, non-flammable and do not stain timber Swell the timber and will cause corrosion of metals until drying out is complete Best used as a preliminary protection followed by kiln drying 25 Organic Solvent Preservative Penetration is excellent provided the timber is quite dry Non-staining不著色, non-corrosive to metals, non-swelling and quick-drying Painting is possible once drying is complete Widely used for remedial treatment Organic solvents are highly flammable and present a fire risk until dried More expensive than the other types Release solvents into the atmosphere. 26
