Zero Force Members

Zero force members are members of a truss structure which do not have internal forces, so they do not contribute to the distribution of forces in the truss. These members are often not wanted in a truss since they only use up extra material which costs money. In some cases these members are wanted in the structure, this can be the case for aesthatic purposes or for extra stability in the structure to prevent buckling of members.

Finding the zero force members in a truss structure

There are a few helpful rules to find the zero force members in a structure. These are listed below:

• When 2 members are colinear and a 3rd one is connected to them in a joint on which no external force is applied, the 3rd member is a zero force member
• When 2 members are non colinear and connected in a joint on which no external force is applied, these 2 members are both zero force members

Example

Let's consider the truss structure from Figure 1, which is connected to the world using 2 pinned supports on the left. And an external force of magnitude F is applied to the structure. In Figure 2, the zero force members of the same truss are highlighted in red. These members were found using the rules mentioned earlier on.

Figure 1. A schematic visualization of a truss structure

Figure 2. The same schematic truss with the zero force members highlighted in red

Extra forces

The same truss structure is now considered but there are more external forces introduced with magnitude F. These external forces are applied on joints that previously had a zero force member connected to it. Since there now is an external force applied to that joint, the zero force members become members that do carry forces. In this case there still is one zero force member which one can find by applying the Method of Joints on the joint in the right upper corner.

Figure 3. A schematic visualization of the same truss structure with more external forces

Figure 4. The same schematic truss with the zero force members highlighted in red

Now is shown what zero force members are and rules to find the zero force members in a simple truss structure are given. See the articles below for more information about truss structures.