Zero Force Members

The members of truss which support no loading are known as zero force members. These zero force members are used to increase the stability of truss during construction and provide added support if the loading is changed.

Zero force members can generally be found by inspection in two cases.

Case-I: If two non collinear members forms a truss joint and no external load or support reaction is applied to joint, then the two members must be zero force members. For example for the following truss by general inspection, we can say that force in members DC, DE and AF, AB will be zero because both D and A joints are formed by two non collinear members and no external load or support reaction is applied on these joints.

Case-II: If three members form a truss joint for which two of the
members are collinear, then the third member will be a zero force member
provided no external force or support reaction acts along this member.
For example: for the following truss ED and DC are collinear members
and no external force or support reaction acts on joint D. So we can say
that force in member BD will be zero. Also if we analyse joint B, then we
can say that it is also formed by three members as force in member BD
is zero and AB, BC members are collinear so force in member BE will be
zero.