The forces carried by the bottom member of a truss are in which type of force?

• A. Compression
• B. Tension
• C. Shear
• D. Bending

Answer: (B)

In a typical truss under downward loading, all members carry axial forces, and the geometry acts like a series of triangles. The bottom chord acts as the tie that keeps the bottom joints from spreading apart as the load pushes the top joints inward. To resist that spreading, the bottom member must develop tension, pulling its endpoints toward each other. The top chord, in contrast, experiences compression as it is squeezed together by the loads. Because truss members are primarily axial, bending or shear in the bottom member isn’t the primary behavior; it’s the axial tension that keeps the structure stable.