Horizontal members in a loaded truss: Depending on loading and geometry, what can be the nature of axial force in the horizontal members shown (tension/compression/zero)?

Introduction / Context:
In truss systems, members are idealized as carrying only axial forces (tension or compression). The sign and magnitude depend on load placement, support conditions, and geometry.

Given Data / Assumptions:

• Planar pin-jointed truss with loads at joints.
• Members are two-force members; shear and bending within members are neglected.
• “Horizontal members” refers to chords/ties that may change nature with load reversal.

Concept / Approach:
Equilibrium at joints and of sections decides the internal axial force. For example, the top chord of a simply supported, uniformly loaded truss is typically in compression, while the bottom chord is in tension. Under different load patterns or support changes, a segment can become zero-force or switch sign.

Step-by-Step Solution:
Analyze joint equilibrium or cut the truss with a section.Compute axial forces; classify as tension (+) or compression (−).Recognize special zero-force conditions (e.g., two non-collinear members meeting at an unloaded joint next to a collinear member).

Verification / Alternative check:
Use method of sections to cross-check a member found tensile by joints; results must match.

Why Other Options Are Wrong:
“Always compressive/tensile/zero” is false; the nature depends on the specific loading and geometry.“Always shear only” contradicts the truss two-force member assumption.

Common Pitfalls:
Confusing sign convention; neglecting that load reversals (e.g., wind uplift) can flip member action.

Final Answer:
Any of the above depending on the case.