Trusses 1 Flashcards
(22 cards)
What must structures resist?
The loads without collapsing or deforming
What do structures transmit?
Loads from their points of application to the supports
What is included in the design process?
- Selection of the structural form and the material
- Determine the external loads
- Structural analysis - internal forces
- Sizing of the structural elements
What are trusses also called?
Pin-jointed frames
What are trusses used in?
Bridges, towers and roofs
What are trusses usually made from?
Steel and timber
What are some commonly used trusses?
- Warren truss
- Howe truss
- K truss
What is the 1st assumption of trusses?
The members of a truss are connected to each other at their ends by frictionless pins
What’s the second assumption of trusses?
External loads are applied to the truss only at its joints
Whats the 3rd assumption of trusses?
The centroidal axes of the truss members meeting at a joint intersect at the pin connection
What is the 1st consequence?
Members of a truss are subjected to axial forces only - apply free body diagram in individual member
How many equilibrium equations for free body diagram of truss member?
3
Why can two equilibrium equation be applied at joints of a truss?
- Each joint will be subjected to a concurrent force system
- For a concurrent force system, there are two equilibrium
How are members usually connected?
Members usually riveted, bolted or welded together (often using plates)
Why can self weight of a truss be neglected or assume to act at the joints?
As self-weight of a truss is usually small compared to other external loads
When is a truss unstable?
If the truss can undergo rigid body motion
What determines if a truss is unstable?
m+r<2j
- The number of unknowns (left hand side of inequality) is less than the number of equations (right hand side of inequality)
When is something externally stable?
When the forces on the supports are neither parallel nor concurrent
When is something internally stable?
If supported appropriately a triangular arrangement of truss members is stable
What do more complex trusses need?
A force analysis
What does it mean if something statically determinate?
- It can be analysed using only the equations of equilibrium
- The number of unknowns are equal to the number of equations
What does it mean when something statically indeterminate?
- It cannot be analysed using the equations of equilibrium alone
- The number of unknowns exceeds the number of equations of equilibrium
