Step 1: Understanding the Concept:
Structural elements are defined by the types of internal forces they are designed to resist.
Axial forces are forces acting along the longitudinal axis of a member (Tension or Compression).
Step 2: Detailed Explanation:
1. Beams: Designed to resist transverse loads, resulting in bending moments and shear forces.
2. Columns: Primarily resist axial compression, but in real structures, they often face bending due to eccentric loads.
3. Truss members: In an ideal truss, joints are assumed to be frictionless pins and loads are applied only at the joints.
This means members do not experience bending or shear; they only carry axial tension or compression.
4. Slabs: Two-dimensional elements that resist loads primarily through bending.
Step 3: Final Answer:
A truss member is the element that ideally carries only axial forces.