BCGBC4010A Apply structural principles to residential low-rise constructions

Structural principles - Properties

Mechanical properties
Strength
The strength of a structural member is the resistance it is able to offer to the load that will just cause fracture, for example, the resistance that 1 mm2 of section can offer to the load that will just cause fracture. This breaking strength is also referred to as 'ultimate strength'. 
Toughness
Toughness can be defined as the resistance to fracture of a material by repeated bending or twisting after its yield point (which is the point at which a material bends or breaks) has been passed. There are several tests for this property, such as observing the number of times a bar of the material will twist prior to fracture, or the number of repeated bendings it can be subjected to under given conditions. Another is the bend test under which a specimen should be capable of being bent through a specified angle and show no sign of fracture.
Elasticity 
Almost all solid materials have some degree of elasticity. A material is said to behave elastically if it deforms with loading and then returns to its original shape when the loads are removed. This ability to behave elastically is particularly important in structural design.
A series of three diagrams is shown to illustrate elastic behaviour. The first diagram shows a picture of a horizontal member. The second diagram shows the member with a load pressure on it causing it to bend. The third diagram shows the member returned to its original horizontal position as the load is removed.
Plasticity
Plasticity is the reverse of elasticity. If a material deforms when loaded and does not return to its original shape when the load is removed, permanent deformation occurs. This is called 'plastic behaviour'. A plastic material will retain exactly the shape it becomes under load even when the load is removed.
A series of three diagrams is shown to illustrate plastic behaviour. The first diagrams shows a picture of a horizontal member. The second diagram shows the member with a load pressure on it causing it to bend. The third diagram shows the same member without the load, however it remains bent and does not return to its original state. The member is slightly bent in the middle. This is permanent deflection.

Ductility
Ductility is the property which enables a material to be drawn out in the direction of its length, for example, wire. It is a valuable property because a ductile material will not fail suddenly or snap off suddenly without giving some warning by lengthening before it fails.
Malleability
Malleability means that a material can be hammered or otherwise worked into various shapes. In some ways this property is similar to ductility. 
Brittleness
Brittleness is the property which causes a material to break or snap off without any noticeable lengthening. It is the reverse of ductility. It is clearly a very undesirable property in building materials, as brittle materials give no warning of approaching failure.
Brittleness is often caused by fatigue, a condition for which there is no exact definition. Fatigue is frequently accompanied by a gradual coarsening of the structure of a material under the stress of repeated vibration. It can be described as a deterioration of mechanical properties which results from the varying and repeated stresses being applied.
Hardness 
The term hardness is usually defined as the degree of resistance to indentation (a gap or space cause by a force being applied) or abrasion (the result of friction by rubbing or grinding which causes material to wear). It is also used to refer to the resistance of a material to scratching. There are several tests for hardness. One of these is to observe the number of times a bar of the material will twist prior to fracture, or the number of bendings it will tolerate under given conditions. Another test is the bend test, under which a sample of the material should show no sign of fracture when bent through a specified angle.

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