BeginnerTopic 12 of 106Engineering Mechanics
Trusses
Frameworks of two-force members that carry only tension or compression.
In depth
Trusses consist of straight members joined at pins and loaded at joints, so each member carries only axial force. Triangles are rigid; the condition m+r=2j gives static determinacy for a planar truss. Used in bridges, roofs and towers.
Key points
- Zero-force members simplify analysis
- Tension pulls the joint away
- Compression buckles slender members
ExampleA Warren truss alternates diagonals in tension and compression.
Trusses carry large spans with little material by using only axial members, so they are common in bridges, roofs and towers.
What is Trusses?
Frameworks of two-force members that carry only tension or compression.
Why is it important to understand trusses?
Trusses carry large spans with little material by using only axial members, so they are common in bridges, roofs and towers.
Why do truss members carry only tension or compression?
The members are pin-jointed and loaded only at joints, so each member acts as a two-force member, and its force must lie along its length.
What makes a truss statically determinate?
When the number of members plus reactions equals twice the number of joints. Fewer members mean a mechanism, and more mean redundancy.
How is Trusses used in practice?
Typical applications include designing a roof truss for a warehouse, checking the members of a bridge truss under traffic load and analysing a tower crane frame for member forces.
What should I learn before Trusses?
Study "Friction" first (topic 11 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Trusses?
Zero-force members simplify analysis. Tension pulls the joint away. Compression buckles slender members.
Can you give an example of Trusses?
A Warren truss alternates diagonals in tension and compression.
What comes after Trusses?
The next topic is "Method of joints", which builds directly on this one.
How difficult is Trusses?
It is classed as Beginner in Engineering Mechanics (topic 12 of 106). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.