Flitched (Composite Timber–Steel) Beams — Purpose in Practice A flitched beam is formed by fastening steel plates to the sides of a timber beam to act compositely. The primary purpose of using a flitched beam is to:

Introduction:
Flitched beams combine materials (typically timber and steel) so that they share bending stresses. Understanding their purpose helps in economical and practical strengthening of existing members without increasing depth substantially.

Given Data / Assumptions:

• Steel plates are rigidly connected to timber so strains are compatible.
• Composite action is achieved (no slip at the interface).
• Analysis uses modular ratio to transform areas.

Concept / Approach:
By adding high-modulus steel plates, the effective section modulus and second moment of area increase. In transformed section terms, this is equivalent to increasing the beam’s effective cross-section, enhancing bending capacity and reducing deflection for the same overall depth.

Step-by-Step Solution:
1) Compute transformed steel area = n * A_steel (n = Es / Etimber).2) Add to timber area to get A_eff and I_eff.3) Increased I reduces curvature (M / E I) and deflection; increased Z = I / y enhances bending strength.

Verification / Alternative check:
Strengthening projects often use side plates or flitch plates to meet moment/deflection limits when depth increase is constrained.

Why Other Options Are Wrong:

• change the shape: incidental, not the goal.
• saving in material: capacity gain, not primarily less material.
• equalise tension/compression strength: not the standard objective in timber–steel composites.
• reduce self-weight: steel increases weight slightly; effect is not significant.

Common Pitfalls:
Assuming flitching is only for tension side; in practice, symmetric side plates are common to maximize stiffness.

Final Answer:
increase the cross-section of the beam