Question

(a) Identify ALL zero-force members, if any, in the two trusses shown below: 10 kip 4 10 kip 12 (b) Identify ALL two-force members, if any, in the two frames shown: 15kN 10 kN | تر 15 | کا Fixed EN *

Answer 1

Solution:-

​​​​(a) Zero force members in the given trusses:-

Diagram 1:-

Since there is no external loading acting at joint C and two members AC and CE are at 180°, member BC is considered to be a zero force member. Once if we think of the given truss without the member BC, member CD also becomes a zero force member and this is followed by same situation for member DE and again member DE will be followed by same situation for member EF. So finally there are four zero force members in the given truss diagram 1. Those are BC, CD, DE and EF.

Diagram 2:-

Since there is no external loading acting at joint D and only two members are connected at D, both members CD and ED will be zero force members. Once if we think of diagram 2 without members CD and ED, at joint E there is no external loading acting and only two members EC and EF are connected at E. Hence both members EC and EF will be zero force members.

Now, coming to joint B there is no external loading acting and two members BA and BC are at 180°. So, member BF would be a zero force member.

Finally there are five zero force members in the given diagram 2. Those are CD, CE, EF, EC and BF.

(b) Two force members:-

Diagram 1:-

Only member AB is a two force member. Obviously, member BC can't be a two force member because there are already two forces acting on the member BC. And, CD is fixed at D and hence CD is also can't be considered as a two force member.

Diagram 2:-

There are no two force members in diagram 2. AC is obviously not a two force member. Since CB is in "L" shape, it is also not a two force member.