The number of zero force numbers in a truss shown below is

SOLUTION

Concept:

Planar Truss: When all the members and nodes of a truss lie within a 2-dimensional plane it is called a planar truss.

Members of a truss carry only axial force. If the member of a truss does not carry any force under some specific load conditions, those members are called zero-force members.

Identification of zero-force members:

1) If at any joint two members are non-collinear and no load is acting at the joint, then both the members will be zero-force members.

e.g.

In the truss shown above, there are two non-collinear members at joint D and there is no load acting at this joint, hence both the members BD and CD are zero force members.

2) If at a truss joint, 3 members are meeting and two of them are collinear and no load is acting at the joint, then the non-collinear member will be a zero-force member.

e.g.

Calculation:

At joint C, there isn’t any load, hence CE and CF are zero force members.

Similarly at joint F, there isn’t any load hence FH and EF are zero force members.

At joint J, there are three members out of which 2 are collinear and no-load at the joint, hence non-collinear member BJ is a zero-force member

At joint D, there is roller support and hence no vertical reaction. So member AD will be a zero force member