Building science wood

Dr f Dejahang (BSc CEng, BSc (Hons) Construction Mgmt, MSc, MCIOB, PhD)

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WOOD The Mechanical properties and availability

of wood have made it a natural material for:

building structures Furniture Tools Vehicles decorative objects Etc

Worldwide it is used more than metal or plastic.

Wood is a natural product and when used responsibly is a sustainable resource which need not result in damage to the environment.

Forests can be protected by recycling and reusing the wood, using less wood and by supporting sustainable forest management

The strength of wood is highly dependent on the loading direction.

Wood is strongest in tension along the fibres and is weakest in the radial and tangential direction.

When loaded in its strongest direction (longitudinal along the grain - wood can have a strength to weight ratio advantage relative to steel of 2:1.

When wood is loaded in other directions (radial and tangential to the grain this advantage disappears.

Wood Types It is customary to describe wood using the

following terms. there is some degree of overlapping in

practice. Carpentry- applying to structural work in

buildings and ships

Timbering - applying to temporary work such as formwork for concrete, gantries and shoring

Joinery -wooden structures inside buildings, such as doors and window frames

Cabinetwork - cabinetry - making furniture

Hardwoods  Hardwood trees are generally broadleaved

trees. These tree species are deciduous, retaining

their leaves only one growing season. The designation Hardwood trees does not

necessarily relate to the hardness of the wood.

Hardwood trees are also called broad leaf trees or deciduous trees.

Typical hardwood trees include:

AshElmsOakMapleWalnutHickorymahogany, and walnut.

Woods grown in tropical climates are generally hardwoods.

Hardwood have shorter fibres’ compared to softwood.

Some hardwoods are evergreen.

Softwoods  Softwoods are one of the botanical groups of trees that have persistent needle-like or scale-like leaves;

softwoods are evergreen and have longer-length fibres’ than hardwoods. 

Softwood trees include pines, spruces, firs, cedars.

The yew is one of the few types of softwood that is native to the UK.

There are a number of softwoods (yew) that are harder and tougher than many hardwoodsLarches, including tamarack, are exceptions, being deciduous "softwoods".

Use of timber in construction

Today, when architects and engineers design landmark buildings like bridges or government offices, schools or Factories, they look to timber to express a contemporary beauty which is nonetheless rooted in nature and a respect for the environment.

The flexibility of lightweight modular timber construction is particularly suited to multi-purpose halls because of its ready adaptability.

Wood is a high-performance material low in weight high in density, with excellent load-bearing

and thermal properties and the availability of a wide range of

timbers, each with its own characteristics, means wood can be suitable for most special requirements.

One specific advantage of wood is its ability to reduce energy use.

Timber construction has a higher heat insulation value than conventional construction methods, even with lower wall thicknesses.

An external wall constructed using timber may have only half the thickness of a brick or concrete wall

yet provide double the thermal insulation value

while at the same time avoiding the thermal bridging common with other construction methods.

Flexibility The flexibility of timber construction

methods makes it easier to vary a building’s orientation on site, its floor plan, the number of rooms, the interior design and the overall appearance

while timber’s thermal efficiency means walls can be slimmer

releasing up to 10% more space than other building methods.

Fire prevention Unlike many other materials, timber

behaves predictably in fire forming a charred surface which provides

protection for the inner structure timber elements can remain intact and

fully load-bearing during a fire. The fire-retardant detailing of modern

timber construction prevents cavity fires and the spread of combustion gases

Sound insulationModern timber buildings readily comply with sound insulation standards through using a layered structure of different materials.

Even more demanding standards can be met using a number of different design solutions.

Durability With good design and correct detailing, structural wood needs no chemical treatment to achieve a long life.

Wood is resistant to heat, frost, corrosion and pollution;

the only factor that needs to be controlled is moisture

Wood is a unique and renewable material

As trees grow they naturally absorb CO2 from the atmosphere

Wood is the building material of the future

The materials used in a typical 2-bedroomed semi-detached house in England emit about 14 tonnes of CO 2 in their extraction and manufacture. 

By using timber frame, you can save up to 9 tonnes per house;

by increasing the amount of wood products such as:

wood windows,doors Flooring They saves still more CO 2Recycling and re-use of wood 

Reconstituted wood-based products

Similarities and differences between steel and timber as structural materials.