Introduction to Trusses

• A truss is a supporting framework for a roof, bridge or any other large structure
• Box and rectangular truss frameworks are inherently weak and susceptible to shear force

The rectangular truss is weak when subjected to shear forces

• The rectangular truss structure can be strengthened by attaching a diagonal tie to it as shown above
• The result is triangular shaped trusses
• Because of their inherent strength trusses are always made up of triangular shapes

A simple truss showing the triangular nature of trusses

• The diagram above shows an example of a simple truss
• The load is prevented from falling by attaching a piece of wire to the cantilever beam
• The compress forces in the truss can only act laterally (horizontally)
• It plays no direct part  in holding this load but it keeps the truss extended

A slightly more sophisticated truss

• The diagram shows a slightly more sophisticated truss
• It was made by adding an extra piece to the truss
• The topmost wire is in tension and the bottom most beam in still in compression
• These two parts hold the entire truss up
• The weight of the load is now supported by the upward action of the tension in the middle wire
• and the compression the diagonal piece (the one to the right in the diagram above)

A truss trellis

• More and more pieces can be added to make an even more complicated truss ( a trellis)
• The diagonal parts of the trellis support the load
• The horizontal wires parts support the trusses
• All the beams resist shear
• The trellis is lighter because unnecessary (neutral components are reduced)

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