Plate Bearing Test – Interpreting an Inflated Tyre Load In a plate bearing (plate load) test for pavement/subgrade evaluation, if the applied load is delivered through an inflated pneumatic wheel (tyre) rather than a rigid steel plate, the loading mechanism most closely corresponds to which idealized plate behavior?

Introduction / Context:
Pavement evaluation often uses the plate bearing test to approximate how real wheel loads affect the subgrade. Conceptually, two limiting load-distribution behaviors are used: a rigid plate, which maintains plane sections and spreads load strongly toward the edges, and a flexible plate, which conforms to the support and tends to apply a more uniform contact pressure. When a pneumatic tyre is used, its deformable carcass and air inflation produce behavior closer to a flexible plate than to a rigid plate.

Given Data / Assumptions:

• Load application through an inflated tyre (pneumatic wheel).
• Purpose: infer the corresponding idealized plate type in the plate bearing analogy.
• Subgrade response considered elastic, homogeneous for conceptual discussion.

Concept / Approach:

A rigid plate forces the foundation to deflect as a near-plane surface; stresses concentrate toward the plate edges. A flexible plate deforms to follow the supporting medium more closely and tends to deliver a relatively uniform pressure distribution over the contact area. An inflated tyre behaves like a compliant membrane on a cushion of compressed air, distributing load more evenly and accommodating local subgrade deformations; this is the hallmark of a flexible plate idealization.

Step-by-Step Solution:

Verification / Alternative check:

Deflection bowls under FWD (falling weight deflectometer) or tyre loads resemble flexible-plate solutions, whereas rigid plate tests show different edge-to-center deflection ratios and stress patterns.

Why Other Options Are Wrong:

• Rigid/semi-rigid: imply limited deformation of the load applicator, not representative of a tyre.
• Semi-elastic: non-standard term in plate test idealizations.

Common Pitfalls:

Assuming all load plates behave rigidly; overlooking tyre pressure effects on contact stress uniformity and shape.

Final Answer:

Flexible plate