Question

Which of the following statements is/are TRUE with respect to the type of stresses to be considered for the design of rigid pavements?

• A. Warping stress due to temperature differential between the top and bottom of the pavement slab as a result of daily variation in temperature
• B. Frictional stress due to the overall increase or decrease in temperature of the pavement slab as a result of seasonal variation in temperature
• C. Critical stress obtained as the maximum of the wheel load stress, the warping stress, and the frictional stress
• D. Critical stress obtained as the sum of wheel load stresses at edge, interior, and corner of the pavement slab

Hint:

Warping stress comes from daily top-bottom temperature gradient; frictional stress comes from seasonal overall temperature change. Design combines wheel load stress with warping stress, it is not a plain maximum or a sum over edge/interior/corner.

Answer 1

The Correct Option is A, B

Step 1: List the stresses that act on a rigid (concrete) pavement slab.
A rigid pavement slab carries three broad categories of stress: wheel load stress (from traffic), warping stress (from a temperature difference between the top and bottom faces of the slab), and frictional stress (from restraint to the slab's own expansion or contraction).

Step 2: Check statement (A), the warping stress.
Warping stress arises because the sun heats the top of the slab during the day and it cools faster at night, so at any given moment the top face and the bottom face are at different temperatures.
This temperature differential tries to curl (warp) the slab, and since the slab is restrained by its own weight and by the subgrade, curling induces bending stress, called warping stress.
This effect follows the daily (day-night) temperature cycle, exactly as statement (A) describes, so (A) is TRUE.

Step 3: Check statement (B), the frictional stress.
Frictional stress is different from warping stress: it comes from the whole slab trying to expand or contract as its AVERAGE temperature rises or falls with the SEASONS (summer to winter), not from a difference between top and bottom.
As the slab tries to change length, friction between the slab and the layer below resists that movement, and this restraint sets up a longitudinal (horizontal) stress in the slab.
This matches statement (B), which is about overall (not top-bottom) temperature change over a seasonal cycle, so (B) is TRUE.

Step 4: Check statement (C).
Design practice for rigid pavements does not just take "whichever of the three stresses is biggest" as the critical stress.
Instead, wheel load stress and warping stress are combined together (added), because both act at the same time (traffic runs on the slab while it is warped by daily heating), and this combined value is checked at the critical locations (edge and corner, day and night cases).
Frictional stress is treated separately from this combination, mainly to design longitudinal steel and joint spacing, since it acts along the length of the slab rather than as a bending stress at the same section.
So describing the critical stress as simply the "maximum of the three" stresses is not how rigid pavements are actually designed, making (C) FALSE.

Step 5: Check statement (D).
Wheel load stresses at the edge, at the interior, and at the corner of the slab are three separate design checks for three different critical wheel positions; a wheel cannot be at the edge, the interior, and the corner all at the same instant.
So these three stresses are never added together as a sum; each is checked, combined with the matching warping stress, on its own.
This makes (D) FALSE.

Final Answer:
Statements (A) and (B) correctly describe warping stress and frictional stress; (C) and (D) misdescribe how the critical design stress is obtained. \[ \boxed{(A), (B)} \]