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

Rigid pavement design has to account for three kinds of stress in the concrete slab: the stress from wheel loads, the stress from temperature warping, and the stress from friction against the layer below. This question checks if you can tell these apart and also checks how they get combined for design.

1. Warping stress from daily top-bottom temperature difference: During the day the top of the slab gets hotter than the bottom, and at night it is the other way round. This top-to-bottom gradient makes the slab want to curl, and the resulting bending stress is exactly what is called warping stress. This description is accurate, so it is true.
2. Frictional stress from seasonal overall temperature change: Over a season the whole slab warms up or cools down as a block, and it tries to get longer or shorter. The subgrade or sub-base under it resists this movement through friction, and that resistance produces a horizontal (frictional) stress along the slab. This is also an accurate description, so it is true.
3. Critical stress as the maximum of the three stresses: This oversimplifies the design method. Wheel load stress and warping stress are added together (not just compared) because both act on the slab at the same time, and frictional stress is checked on its own for a different purpose (steel and joint design), not folded into that combined figure or taken as a plain maximum. So this statement does not match design practice and is false.
4. Critical stress as the sum of edge, interior and corner wheel load stresses: Edge, interior, and corner stresses correspond to three different, mutually exclusive positions of the wheel load on the slab. Only one of them applies at a time for a given loading case, so they are never summed; this statement is false.

Let's summarize:

• Warping stress: from daily top-bottom temperature gradient.
• Frictional stress: from seasonal overall temperature change, resisted by friction with the layer below.
• Design combines wheel load stress with warping stress (not a plain maximum of three, and never a sum over edge/interior/corner).

So only the first two statements are correct.