Wood is the most widely used building material, second only to stone. Wood’s diverse properties and its characteristics make it ideal as a long-lasting building material.
But, be careful not to get caught up between wood and timber; it is a type of wood that is used for carpentry or construction applications. Likewise, the term “wood” is used to describe the furniture and other non-structural objects. The term “wood” and “timber” is also commonly referred to as wood and timber in North America.
Chemical Composition
Cells, or wood fibers, are mostly cellulose that is cemented with an ingredient called lignin. The wood structure comprised 70 percent of cellulose, 12 to 24 percent lignin, and as much as 1% ash-forming substances.
These components provide outstanding hydrolytic properties, as well as their durability and resistance to decay. The bond between fibers is so solid that when they are put under tension, they tend to break apart instead of becoming separated.
Hygroscopic Properties of Wood
Wood is hygroscopic, which means the wood expands as it is absorbed by moisture, and shrinks when it dries or sheds its moisture. This characteristic affects the final use of wood.
The various hygroscopic characteristics of wood include the content of moisture and fiber saturation point the equilibrium content of moisture, shrinkage, swelling, and so on.
The moisture content of the timber
The content of moisture in timber is the amount of water it consists of in proportion to the weight of timber when it is dried in the oven.
The moisture content in wood is an important property for the construction and design of timber structures.
Fiber Saturation Point
The timber’s water is typically found in two kinds:
- As water that is free in Cell cavities.
- In the form of water absorbed by cell fibers.
As the wood dries, its cells release the water that they have absorbed only after all free water has been eliminated, and surrounding cell cavities are empty. The point at which fibers are completely saturated, however, the cell cavities are empty, this is referred to as the point of saturation for fibers.
The moisture content at the fiber saturation point differs between different wood pieces different pieces within a particular spice and also between species kind, a level of 30 percent moisture content is usually connected with an area of fiber saturation. This situation is that it is the point where shrinkage starts.
Equilibrium Moisture Content (EMC)
When the tree is cut down and then cut into the wood the moisture content starts to decrease as the moisture within the wood is lost to the air surrounding it. The wood will continue to absorb or release moisture until the wood is at a level that is in equilibrium with the moisture that is in the atmosphere. The wood’s moisture content in this stage is referred to as the equilibrium content of moisture (EMC).
It is essential to determine the equilibrium moisture content at the specific location since it helps to forecast the level of moisture content of wood it will attain during its time of use. To ensure that the wood is not subject to any alteration in dimensions, it ought to be dried at a moisture content that is as close as feasible to the water content in equilibrium (EMC).
Shrinkage and swelling
The expansion or shrinkage that occurs in the direction of the grain (Longitudinally dependent on the tree’s height) is almost non-existent and is not significant for construction purposes. However, over the grain, the wood will shrink significantly in width and thickness. Shrinkage is the main element that is seen in the direction of the tangent from the rings that are annual. it can affect up to two-thirds or more of the rings (radial) in the wood.
Physical Properties of Wood
The diverse characteristics of the wood include specific directional characteristics, dimensional changes as well as density and gravity.
Directional Properties
Wood is an anisotropic material because of its cell structure.
The structure of wood of any particular piece is thought to comprise three different axes to symmetry, such as
- Longitudinal: Parallel to Grain.
- Radial: Perpendicular to Grain and Radial to Annual Rings.
- Tangential: Perpendicular to Grain and Tangential to Annual Rings.
Logs cut from wood are generally placed to have their longitudinal length (or faces) roughly parallel to the long axis of the log, However, some faces might appear asymmetrical with respect to the tangential and radial directions.
To be practical, the wood’s directional properties can be differentiated between perpendicular as well as parallel to the grain (Longitudinal). Perpendicular to grain properties typically are used to evaluate its radical and tangential characteristics.
Dimensional Changes
The changes in dimension in wood occur because of the variations in temperature and moisture. The majority of wood that has moisture reacts to temperature variations in a different way as a different building material.
When wood is heated it expands (swells) because of temperature. It also shrinks due to the disappearance of water. If the wood is dry at first and shrinkage is due to the loss of moisture due to heating will be greater than thermal expansion. This is why the net dimension changes take place within the wood.
In the design of timber, dimension changes caused by temperature are considered to be small when compared to the dimensional change caused by changes in moisture content.
Wood shrinks when it loses moisture, and expands as it absorbs water at the point of saturation and an oven-dry condition. There is no change in the dimensional form when the moisture content changes beyond the point of saturation for fibers. The amount of shrinkage and swelling is different in the radial, longitudinal and tangential directions of the piece of wood or lumber.
Density
The wood density is determined by calculating the weight per volume. It is sometimes referred to as bulk density or weight density.
Specific Gravity
A wood fiber has a particular gravity of 1.5 and is much heavier than water (Specific gravity of water = 1). However, dry wood from the majority of species can be found floating in water since a significant portion of the area is occupied with air-filled chambers.
The spectrum of the specific gravity of the majority of wood species is 0.36 to 0.70 when it comes to oven drying. Specific gravity is a rough measure of wood materials that are solid and is a general indicator of their strength properties.
Mechanical Properties of Wood
The wood’s mechanical properties are the ability of wood to resist an external or external force. It is the impact of a particular object of materials that tends to deform when subjected to an external force. It is the properties of wood that make it ideal for the construction of materials as well as furniture components.
The Strength Properties of Timber
The strength properties of timber define the absolute resistance of the material to loads. They are the material’s behavior in relation to compression, tension shear, and bending, as well as torsion as well as shock resistance.
Like other properties of timber, Strength properties are most likely to vary across three major directions, i.e. Longitudinal, Radial, and Tangential. The differences between radial as well as tangential directions are minor and random when cutting a tree into lumber or wood.
Compression
Wood may be compressed in the direction perpendicular to the wood grain or parallel to the wood grain, or at an angle relative to the grain of the wood.
Perpendicularly to Grain: If compression is applied perpendicularly to the grain of the wood, it causes stress that causes deformation of the wood cells that are perpendicular to their length. Wood cells break down at low levels of stress when loads are involved in this direction.
Wood deforms to around half its original thickness prior to the time when complete cell collapse happens. According to Charles Arntzen’ (Author of the book titled Encyclopedia of Agricultural Science) when compression is applied perpendicularly to the grain, failure occurs depending on the limits of performance, which are 0.04-inch deformation.
Parallel to the Grain: When compression is applied parallel to the grain it creates stress that causes deformation of those wood cells on their longitudinal axis. Then, every wood cell is an independent hollow column that receives lateral support from adjacent cells as well as from its internal structure. This is why the deformations are largely due to an internal crushing process of intricate cell structure when it fails.
An Angle to Grain A compression angle applied to the grain causes stress to be perpendicularly and perpendicular to the grain. Thus, the strength of the compression in an angle that is applied to the grain can be considered to be the value that is between perpendicular and parallel to the grain.
Tension
The wood is solid in tension when it is it is parallel to its grain. failure can occur due to a complex mix of the two types like
- Failure of the cell wall
- Cell-to-cell slippage
The process of slippage occurs when adjacent cells slide over one another, while cell wall failure is caused by the rupture of the wall of the cell. In both types of failure, small or no deformations are observed happening prior to the completion of the break
Shear
Shear is a force that acts on timber in 3 ways i.e. vertical, horizontal, and rolling.
Horizontal shears are the main shear in wood. It operates along the grain. It causes the upper part that is the subject to move around the lower one by breaking the intercellular bonds and forming the structure of the cells of the wood.
Vertical shear is rarely thought of as a failure because a different one i.e. the compression perpendicularly to grain nearly always occurs prior to cell wall ruptures when shear is vertical.
In addition to the horizontal and vertical shears, a less typical type of shear, also known as rolling shear is also found in wood. It’s caused by forces that are perpendicular to the cell’s length in a plane parallel to the grain of the wood.
As per the USFS Timber Bridge Manual written by the United States Forest Service (It is an agency of the US Department of Agriculture) Wood is a weak material for shear rolling, and the failure is preceded by significant deformations in the cell’s cross-sections.
Bending
If wood is loaded through bent, the part of the wood that is on that side is stressed with compression that is parallel to the grain while the opposite side is not stressed in tension in a parallel direction to the grain.
The bending process also causes horizontal shear that is parallel to the grain as well as compression perpendicular to the grain at the support. A typical failure sequence for simple bending is that of the formation of compression failure, followed by the formation of visible wrinkles in compression. This increases the area of compression and reduces the tension zone. This will eventually lead to the failure of tensile.
It is Resistant to Energy Absorption The energy absorption or the resistance to shock of wood is the ability of it to absorb and release energy through deformation rapidly. The wood is extremely durable in this regard which is why it frequently is the preferred material to absorb shocks.
Elastic Properties of Timber
The properties of wood that are elastic are dependent on the resistance of timber to deformation when stressed and the capacity of timber to recover its original size or shape when stress is lifted.
Being an isotropic substance with identical properties across all directions, the elastic wood’s properties are outlined through three constants of elasticity, such as the modulus of elasticity as well as shear modulus and Poisson’s ratio.
Modulus of Elasticity in wood is determined by the strain placed on one axis to the strain that occurs along the same axis.
Shear Modulus Shear Modulus of the timber is correlated with the shear stress as well as the strain.
Poisson’s Ratio: Poisson’s Ratio of timber is correlated to the parallel strain applied in relation to the strain lateral.
Decorative Property of Wood
The decorative quality of wood is based on the color, luster, patterns, texture, and finishes, as well as the stain’s capacity to accept filler and the technique of cutting or cutting.
It is not possible to provide an exact color description of all kinds of wood due to the fact that it contains a variety of shades and colors. of textures.
Acoustical Properties of Wood
The properties of wood’s acoustic are affected by its absorption capacity and the ability to soundproof. Sound absorption capacity is the quantity of sound that hits a surface that does not reflect off the surface. The ability to soundproof reduces the sound’s intensity when it travels through an obstacle.
The sound insulation properties of construction materials are measured in decibels at different frequencies. Wood by itself is not able to provide great sound insulation like other building materials.
In accordance with the Timber Construction Manual, which was developed through the American Institute of Timber Construction If the wood is used in conjunction with other construction materials it will offer a pleasing sound-insulating capability. The absorption capacity of wood fluctuates with variations in the density the content of moisture, density, as well as the orientation of the grain.
Electrical Properties of Wood
The most crucial characteristics of wood’s electrical energy are its dielectric properties as well as resistivity to currents. The resistance to electric current in wood varies with humidity, temperature, and the direction of the electric current in relation to the grain’s direction.
The dielectric properties of wood are used in the drying of the wood as well as the high-frequency curing of adhesives within laminated members that are glued. The property of electrical resistance in wood is utilized in electronic moisture meters to gauge the content of water. It also changes depending on the change in moisture content in particular below the point of saturation for fibers and decreases in electrical resistance when there is an increase in the moisture content.
To summarize
Timber is among the most reliable and oldest construction materials utilized for various kinds of construction projects since the time of the ancients. Wood for building materials comes with numerous advantages over other construction materials. It is easily available in a renewable manner as well as having durability as well as functional strength as well as being light in weight when compared to bricks and concrete construction materials.
Construction industries across the globe are focused on the creation and use of environmentally friendly construction materials to ensure that their production doesn’t create any environmental risks. It is an incredibly renewable, eco-friendly material and is among the most sought-after building materials in construction.
