Meaning
Design parameters in concrete pavement engineering measure the stiffness of a concrete slab relative to the elasticity of the underlying subgrade. The relative stiffness radius determines how widely a concentrated wheel load is distributed across the slab and how much bending stress is generated in the concrete. This value is a fundamental input in the Westergaard equations used to design industrial and airport pavements.
Analytical Calculation
Calculating the radius involves the slab thickness, the modulus of elasticity of the concrete, and the modulus of subgrade reaction. This formula balances the bending resistance of the concrete against the compressibility of the soil. The resulting length value represents the distance from the load where the slab deflection becomes negligible.
Adjusting this value helps optimize slab design for different heavy machinery wheel layouts.
Load Distribution
A larger radius of stiffness means the slab can distribute a concentrated load over a wider area of the subgrade. This reduces the maximum pressure on the soil and prevents localized settlement. It allows the pavement to carry heavier loads without cracking.
Foundation Influence
If the subgrade loses its stiffness due to moisture or erosion, the radius of stiffness will change. This change alters the stress distribution in the concrete. It can lead to premature failure if the soil is not stabilized.
