Beams built from two or more different materials, rigidly connected to act together as a single unit under bending, are called composite beams.

Introduction / Context:
Engineering practice often combines materials (e.g., steel–concrete, timber–steel) to optimize stiffness, strength, weight, or cost. When elements are connected so there is no slip at the interface and they bend together, the assembly behaves as a single member called a composite beam.

Given Data / Assumptions:

• Two or more materials are used.
• Rigid connection prevents interlayer slip (full composite action).
• Plane sections remain plane (compatibility across materials via transformed-section method).

Concept / Approach:
Composite behavior requires shear transfer at the interface (e.g., studs in steel–concrete). Analysis uses modular ratio n = E1/E2 to transform areas and compute stresses/deflections as if the section were homogeneous under the assumption of perfect bond.

Step-by-Step Solution:
1) Define objective: different materials to share bending based on stiffness.2) Ensure composite action: provide connectors to prevent slip.3) Use transformed section: A2' = n*A2 to compute neutral axis and section modulus.4) Evaluate stresses with sigma = M*y / I_transformed, respecting each material's allowable limits.

Verification / Alternative check:
Load tests show reduced deflection versus noncomposite action, confirming stiffness gain from composite behavior.

Why Other Options Are Wrong:

• Compound beams: Term sometimes used for built-up beams of the same material; not specific to multi-material action.
• Indeterminate/Determinate beams: Describe static determinacy, not material composition.

Common Pitfalls:

• Assuming full composite action without adequate connectors.
• Ignoring differential shrinkage/creep between materials.

Final Answer:
Composite beams.