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Timber is one of the oldest and most widely used building materials in construction due to its strength, durability, workability, and aesthetic appeal. However, like all natural materials, timber is susceptible to various defects that may reduce its strength, durability, appearance, and service life. These defects may arise during the growth of the tree, during seasoning, or after conversion and use. Understanding the nature and causes of defects in timber is essential in building services and maintenance to ensure structural safety, longevity, and cost-effective upkeep of buildings. Defects in timber can broadly be classified into natural defects, defects due to seasoning, defects due to conversion, and defects caused by biological agencies. Natural defects develop during the growth of the tree and are often unavoidable. One of the most common natural defects is knots. Knots are formed at the base of branches and represent portions of branches embedded in the trunk. They may be sound knots, which are firm and tightly intergrown with the surrounding wood, or dead knots, which are loose and may fall out. Large and numerous knots reduce the strength of timber, especially in structural members subjected to tension and bending. They also affect the appearance of finished surfaces and may create difficulties in machining and finishing. Shakes are another important natural defect. Shakes are cracks or splits that occur in the wood due to stresses developed during growth or due to external forces such as wind. Heart shakes originate at the pith and extend outward toward the sapwood. Star shakes start from the outer surface and extend inward along the medullary rays. Ring shakes, also known as cup shakes, occur along the growth rings, separating one annual ring from another. Shakes weaken the timber by reducing its resistance to shear and bending stresses and allow _______ ________ ________ __________ _____ ___ ______ ______ _______ _____ _______.
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