Example of a compressive force acting on a structure: Legs of stool
Factor of safety
Why is it important? To take into account unforeseen extra loading
the structural capacity beyond the expected load
How much stronger is the structure than the expected load
Ratio of maximum strength to the intended design load
Features to be considered when calculating factor of safety (building a bridge)
maximum amount of vehicles on bridge at any one time
dynamic loads caused by weather conditions
potential movement of ground supporting the structure
increase in weight of HGVs (heavy goods vehicle – a truck over 3500kg) in the future
choice of materials used
Honeycomb cells: door panel inner
Method of reinforcement: Bracing; Example: Diagonal member of a gate
Reinforced beam: Construction of bridges/buildings, Lintel
‘I’ Section beam: steel framed buildings, joists in a building structure
the maximum forces on the beam act at its outer limits therefore the beam needs a greater area of material there to distribute the greater loading more efficiently
Box section beam: table leg, column, pillar
Example of the use of a strain gauge: Deflection of an aircraft wing
Shell structures: car body, tanker, boat hull
Define Moment (turning forces): force x perpendicular distance to pivot
Explain the need for triangulation in structures.
increases rigidity
and limits the tendency to buckle
distribute loading
Properties of mild steel: elasticity
Example of a permanent fixing method: welding; to join members in a framework for a railer chassis
Redundant member: A member that has no structural purpose so that if it were removed, the integrity of the structure would not be compromised.
Strain: the change in length of a sample due to an external force divided by the length before the force is applied
Importance of washers when using nuts and bolts
Distribute the load; over a wider area; to reduce stress on the component
Joining methods:
Nut and bolt – no heat involved, can be removed if necessary
Rivet – permanent method, can be either hot or cold process
Welded joint – permanent method, gives a strong, flush surface
Why wood is a suitable material for house framework
durable, particularly when protected
strong in tension and compression
will allow movement in foundations without losing strength
easily worked and can be prepared offsite in controlled conditions
Calculating reaction
Make RA + RB = the load/force in Newton
Force x distance to RA = RB x distance to RB
Solve for RB and subtract it from the total load
Advantages of using a composite material such as carbon fibre for a bicycle frame
increased stiffness
durability
weight reduction
shock absorbing properties
consistent quality
will not corrode due to weather conditions
allow increased strength, higher strength to weight ratio
When loaded, the cable is said to behave elastically. Explain what this means in structural terms.
beam will stretch under applied load
but will return to its original shape and size when the load is taken off without any permanent deformation
IGCSE REVISION 