Technology Grade 8

Key concepts for structures:

• Frame structures are made up of severa members.
• Each member of a roof truss performs a particular function in a truss.
• The four different forces that may act on structures are tension, compression, shearand torsion forces.
• Each different force has a different effect on the members of trusses.
• There is a simple method to identify tension and compression forces in members of trusses.
• Trusses need structures that form triangles in order to be rigid.
• Electrical pylons need to include triangular forms (triangulation), so that they can be rigid.
• Cross-bracing in electrical pylons makes them resistant to torsion forces.
• Several very different structures are used to span spaces.
• Structures can fail from a lack of strength (they can fracture), a lack of stiffness or rigidity (they can bend) or a lack of stability (they can fall over).