Determination of the Internal Forces in Truss Members
1- Method of Joints
This
method is a systematic method and applicable for all types of trusses but it is
considered as a slowly analyzing method. This method
depends on applying the equilibrium conditionsto the free body diagramof each joint of the truss.
In order to simplify the analysis in this method, zero-force members (vanishing internal force members) should recognized toreduced the number of unknowns. It should be noted thatthe loading determines whether a member is a zero-force member or not.
The following rules are useful in identifying zero-force members.
1.Any non-collinear two members at an unloaded joint (Fig. 1a in the attached file), then both members are zero-force members.
2. If two membersconnected at a loaded joint as
shown in (Fig. 1b in the
attached file) and the action line of the external force (F) coincideswith the direction of one of these members, then the other member is a zero-force member.
3. Let three members be connected at an unloaded joint as shown in (Fig. 1c in the
attached file). And two members of
them have the same direction,then third member is a zero- force member.
Please see the attached file.
References
1- R.C. Hibbeler,
2004 " Engineering Mechanics – Static", Pearson Education. Inc.
2-Dietmar Gross, et., al.,
2009 "Engineering Mechanics 1-Static"Springer Heidelberg Dordrecht
London New York.