Materials (Timber)

Materials - Timber




IF anyone is interested in a kind of 'short' informative account on timber that I made by summarizing some points from 'Materials for Architecs & Builders'. A thousand (ish) words of revision for the exam. Seriously more than enough knowledge, but it can always be useful for future design projects (enjoy): I got seriously bored of reading about timber so I found the time to draw something really random. I think I will do some reading on masonry, steel, iron, concrete and glass after I had recovered from timbering.

__________________________________________________

TIMBER:

Timber: versatility, diversity & aesthetic qualities make it an important building material. Additionally it is renewable and uses little energy in production. An important fact is that it once used to be a living organism. Essentially, its strength is created by the cell-walls that are formed by microfibrils.

Hardwoods: Botanical classification. (Angiosperms) are usually found in temperate and tropical climates. They take about a lifespan of a human to mature and are deciduous. The cells of hardwoods have complex structure different types of cells for differing functions. There are two different types of hardwoods: diffuse porous and ring porous.

Softwoods: Botanical classification. (Gymnosperms) are usually found in temperate and colder regions. They take half a human lifetime to mature and are evergreen conifers, so do not shed their leaves. Differences between softwoods and hardwoods can only be truly found while inspecting them at a microscopic level: the cells of softwoods are of a single type that varies in size.

‘Shelterwood’ method: Is a staged harvest over several years, which ensures replacement of the trees.

Types of cut: Plain Sawn & Quarter Sawn: Plain sawn if the growth rings meet the surface at less than 45 degrees, Quarter sawn is cut so that the growth rings meet the surface at more than 45 degrees. The most economical way of cutting timber is to use the through and through method. This produces both PS and QS. Quarter Sawing is more expensive, but is harder than PS. If the centre of the tree is soft and weak, it is removed as a boxed heart.

Sizes: Softwood sizes are quite specific and do not normally exceed 5m in length or 225mm in width. Hardwoods, on the other hand, are more variable, because of their diversity and the fact they are imported in random lengths/widths.

Moisture content and seasoning: air & kiln: Being a living organism, the weight of water within is larger than its dry weight. The controlled loss of moisture from green timber to the appropriate moisture content for use is called seasoning. The aim is to create compatibility with the conditions in which it will be used, so that movement will not be noticeable. Additionally, when the water content is less than 20% will stop any fungal activity. However, (drying), seasoning timber isn’t always easy, since it has to be controlled so that it doesn’t crack, because the outer layers shrink while the interior is still wet. There are two different ways of seasoning: air seasoning, which takes about 3 months for softwoods and a (few) year(s) for hardwoods, and kiln drying, which takes considerably shorter: few days for softwoods and a few weeks for hardwoods.

Moisture movement: Softwoods & Hardwoods are classified according to the sum of their different types of moisture movement. The larger the woods moisture movement is, the greater its distortion.

Timber defects: There are three different types of defects in traditional (untreated) timber.
·
Natural defects: Knots, natural inclusions, abnormal growth rings, tension and compression are some of the different natural defects of timber.
·
Conversion defects: Sloping grain and wane are two conversion defects. If the grain slopes, the timber loses bending strength. Waney edges are the loss of a part of the edge of timber.
·
Seasoning defects: Different types of shakes may occur when seasoned. These are major splits.

Modified timber: The physical properties of timber can be modified.

Deterioration: The following can cause timber to deteriorate: weathering, fungal attack, insects and fire. When weathered, timber loses its colour and becomes grey. When moisture moves in timber in cycles of dry and wet, cracks can form on the surface, which exposes it to fungal attack. Fungi break down organic materials in order to produce nutrients and survive. There are several ways in which fungi can break down the organic matter in timber, but eventually this lead to loss of structural strength and death, if it is still a live tree. Insect attack is similar to fungal attack, but less serious, because usually they do not reproduce as quickly, and cause less damage. Fire is rather obvious, since it burns the timber destroying it.

Timber Products: There are many products manufactured from timber. Many of these products are made from small timber sections or by-products from timber conversion. There is a very big range of products which are used in different ways in construction.

Laminated timber: Laminated timber sections are both stronger and longer than traditional lumber, which is usually not readily available or might have defects. This type of timber is created by gluing small timber sections together with a resin adhesive. Additionally glue laminated timber has a good fire performance. The majority of laminated timber is made from softwoods such as European redwood or whitewood, and can span over 50 metres.

Cross-laminated timber: Panels can be made from cross-laminated timber in a similar way than conventional plywood, but in a larger scale. Hence they can easily be structural and their maximum size depends on the physical capability (size) of the factory.

Laminated Veneer Lumber: (LVL): Also known as microlam, is more economical than laminated timber. It is manufactured under heat and pressure by laminating timber strands with polyurethane resin. This is a very versatile material that can be used for columns, beams, purlins and trusses, since it can easily span 26 metres.

Plywood: Plywod is produced by peeling a log, creating a thin sheet that can be used in construction for panels. These panels are rather resistant to fire and can be used to protect steel from heating rapidly and losing its strength.

__________________________________________________

I got seriously bored of reading about timber so I found the time to draw something really random. I think I will do some reading on masonry, steel, iron, concrete and glass after I had recovered from timbering.