Timber Project Essay Research Paper 1

  • Просмотров 306
  • Скачиваний 5
  • Размер файла 17

Timber Project Essay, Research Paper 1. Timber has been a building material since man first came out of his cave. The reasons for this are due to timber being a plentiful product and the properties it holds, being that timber is high in strength, light weight, and reasonably durable. Timber can be cut and shaped easily without the use of machines. Prehistoric man found that these properties were ideal for building houses, boats, and bridges. Timber is now has many different uses, including paper, furniture, doors, windows, decorative objects and structural members etc. The uses for timber is endless and as long as the replanting continues and our resources are retained generations to come will enjoy the benefits timber has given us. There are two classes of timber:

Gymnosperms (Evergreen, softwood, conifer) These are the most primitive type of tree, the leaves are in the form of needles they have one main stem and a conical shape to the crown e.g. Douglas fir quite quick to grow. Angiosperms (deciduous hardwood) These are flowering plants and are more advanced in evolution than conifers. They have broad leaves, multiple stems and a globular crown shape. E.g. Oak, Walnut. Slow to mature and expensive to purchase compared to softwood. In a living tree the sapwood is just under the bark of the tree. The sapwood is the trees transportation system for nutrients, sugar and water. The heartwood in the centre of the trunk provides structural stability for the tree. The sapwood next to the heartwood is in the process of being converted to heartwood.

The sapwood has a higher MC than the heartwood. 2. Properties of timber Tensile strength The tensile strength of wood is not great. The molecular structure of the cells of the wood tear apart easily but can be compressed with a high amount of force before the wood disfigures. Beams used in extreme tension are commonly made of steel or re-enforced concrete. Timber can have extreme variations in strength with different species of wood and different parts of the tree. 3. Compressive strength The compressive strength of wood in an average piece of timber with a density of 513 kg/m| has the compressive strength of 30 – 40N/mX Timber has a higher compressive strength than tension strength due to the wood being cellular. The cells can grip on to each other holding the wood together.

Concrete has a greater compressive strength than timber but less in tension. Years ago the wood strength was not known, this lead to the over specification of many buildings, and wasting valuable resources. With today s technology materials can be used to their maximum potential minimising waste and over specifying. 4. Elasticity Timber is an elastic material, which means when a mass is put on a piece of timber it deflects and when the mass is removed the timber returns back to its original position, up to a certain well defined limit of stress. The yield stress point can vary on the size, and type of timber. Timber can vary in strength. So often the stress grading of the timber is greatly under estimated. 5. Water Absorption It is recommended that the moisture content of timber

be kept below 20%, if any greater amount of moisture is present then rotting and insect infestation can occur; the normal average moisture content is 12%. The ventilation of the wood is a very important aspect of design, if timber is kept dry and ventilated it can last a considerable amount of time. The weight of dry wood = Wd The moisture content = MC The moisture weight = Wm MC = Wm Wd . 100% a. Wd Timber which has moisture content of 100% means that the weight of the water is equal to the weight of the wood. It is possible for timber to have several hundred percent MC. The loss and gain in moisture within the wood causes shrinking and swelling in all directions this can cause many problems and have severe consequences 6. Water repellent Naturally wood absorbs water and does