Pin Jointed Structures

Question 1

Define a Moment

Answer 1

A rotational force acting around a single point

Question 2

Define a Roller Pin

Answer 2

Is a pin that is fixed in place in the y direction, but allowed to slide in the x direction and rotate.

Question 3

In which direction(s) does a roller pin have reaction forces

Answer 3

In the y direction only.

Question 4

Define a Built-in Pin

Answer 4

Are entirely fixed (eg welded joint).

Question 5

In which direction(s) does a built-in pin have reaction forces?

Answer 5

Has rection forces in the x and y direction as well as a moment.

Question 6

Define a pin-jointed structure

Answer 6

A structure where the joint is pinned, or free to rotate.

Question 7

Define a Truss

Answer 7

A truss is an assembly of many bars.

Question 8

Describe Roller pin diagram

Answer 8

Has a triangle below the bar with two balls below the triangle.

Question 9

What does the symmetry of the bar forces in a pin-jointed frame depend on?

Answer 9

1 - symmetry of the structure
2 - symmetry of the loading
Both conditions need to be satisfied for the bar forces to be symmetric.

Question 10

Define a zero force member

Answer 10

Zero force members are members which do not have any force on them.

Question 11

Define a Two Force Member

Answer 11

A two-force member is a body that has forces (and only forces, no moments) acting on it in only two locations.

Question 12

Define a Three Force Member

Answer 12

A Three Force Member is where three non-parallel forces act on a body.

Question 13

Define a Pin Joint.

Answer 13

A pin joint is a connection between two objects that allows only relative rotation about a single axis.

Question 14

Define Compression

Answer 14

In mechanics, compression is the application of balanced inward (“pushing”) forces to different points on a material or structure, that is, forces with no net sum directed so as to reduce its size in one or more directions.

Question 15

Define Tension

Answer 15

Tension is the pulling or stretching force transmitted axially along an object such as a string, rope, chain, rod, truss member, or other object, so as to stretch or pull apart the object.

Question 16

Describe a Fixed Pin Diagram

Answer 16

Has a circle attached to the bar with a triangle beneath.

Question 17

Describe a Built-in Pin diagram

Answer 17

Has the bar in contact with the theoretical surface with no additional symbols.

Question 18

How to deal with externally applied moments.

Method

Answer 18

In the same way as external forces, but only contribute to moment equations. (Set moment equations to zero).

Question 19

Define a Distributed Load

Answer 19

Is applied uniformly to a bar, or a section of a bar. As far as external forces are concerned (i. e. forces in other bars and reactions), it can be represented by a single force through its midpoint. This is a simple way to represent the self-weight of heavy bars.

Question 20

Calculating Vertical equilibrium with a distributed load.

Equation

Answer 20

Value of dist. load x length of dist. load = weight for equation

Question 21

Calculating moment equilibrium with a distributed load

Equation

Answer 21

value of dist. load x length of dist. load x distance from turning point = moment

Question 22

Calculating loads within a bar using nodes

Answer 22

• When loads are applied within a bar, we can determine equivalent node forces using equilibrium.
• Look for forces at the nodes that produce the same net force and moment equations as the original loading.