Trusses 1

Question 1

What must structures resist?

Answer 1

The loads without collapsing or deforming

Question 2

What do structures transmit?

Answer 2

Loads from their points of application to the supports

Question 3

What is included in the design process?

Answer 3

1. Selection of the structural form and the material
2. Determine the external loads
3. Structural analysis - internal forces
4. Sizing of the structural elements

Question 4

What are trusses also called?

Answer 4

Pin-jointed frames

Question 5

What are trusses used in?

Answer 5

Bridges, towers and roofs

Question 6

What are trusses usually made from?

Answer 6

Steel and timber

Question 7

What are some commonly used trusses?

Answer 7

• Warren truss
• Howe truss
• K truss

Question 8

What is the 1st assumption of trusses?

Answer 8

The members of a truss are connected to each other at their ends by frictionless pins

Question 9

What’s the second assumption of trusses?

Answer 9

External loads are applied to the truss only at its joints

Question 10

Whats the 3rd assumption of trusses?

Answer 10

The centroidal axes of the truss members meeting at a joint intersect at the pin connection

Question 11

What is the 1st consequence?

Answer 11

Members of a truss are subjected to axial forces only - apply free body diagram in individual member

Question 12

How many equilibrium equations for free body diagram of truss member?

Answer 12

3

Question 13

Why can two equilibrium equation be applied at joints of a truss?

Answer 13

• Each joint will be subjected to a concurrent force system
• For a concurrent force system, there are two equilibrium

Question 14

How are members usually connected?

Answer 14

Members usually riveted, bolted or welded together (often using plates)

Question 15

Why can self weight of a truss be neglected or assume to act at the joints?

Answer 15

As self-weight of a truss is usually small compared to other external loads

Question 16

When is a truss unstable?

Answer 16

If the truss can undergo rigid body motion

Question 17

What determines if a truss is unstable?

Answer 17

m+r<2j
- The number of unknowns (left hand side of inequality) is less than the number of equations (right hand side of inequality)

Question 18

When is something externally stable?

Answer 18

When the forces on the supports are neither parallel nor concurrent

Question 19

When is something internally stable?

Answer 19

If supported appropriately a triangular arrangement of truss members is stable

Question 20

What do more complex trusses need?

Answer 20

A force analysis

Question 21

What does it mean if something statically determinate?

Answer 21

• It can be analysed using only the equations of equilibrium
• The number of unknowns are equal to the number of equations

Question 22

What does it mean when something statically indeterminate?

Answer 22

• It cannot be analysed using the equations of equilibrium alone
• The number of unknowns exceeds the number of equations of equilibrium