Module 4: Pavement Design

Lecture 29 Rigid pavement design

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Temperature stresses

Temperature stresses are developed in cement concrete pavement due to variation in slab temperature. This is caused by (i) daily variation resulting in a temperature gradient across the thickness of the slab and (ii) seasonal variation resulting in overall change in the slab temperature. The former results in warping stresses and the later in frictional stresses.

Warping stress

The warping stress at the interior, edge and corner regions, denoted as $\sigma_{t_i},~\sigma_{t_e},~\sigma_{t_c}$ in kg/cm$^2$ respectively and given by the equation 2-3.

$$\sigma_{t_i} = \frac{E\epsilon t}{2} \left( \frac{C_x + \mu C_y}{1-\mu^2}\right)$$ (1)

$$\sigma_{t_e} = \mathrm{Max~}\left(\frac{C_x E \epsilon t}{2} , \frac{C_y E \epsilon t}{2} \right)$$ (2)

$$\sigma_{t_c} = \frac{E \epsilon t}{3(1-\mu)}{\sqrt{\frac{a}{l}}}$$ (3)

where $E$ is the modulus of elasticity of concrete in kg/cm$^2$ (3$\times$10$^5$), $\epsilon$ is the thermal coefficient of concrete per $^o$C (1$\times$10$^{-7}$) $t$ is the temperature difference between the top and bottom of the slab, $C_x$ and $C_y$ are the coefficient based on $L_x/l$ in the desired direction and $L_y/l$ right angle to the desired direction, $\mu$ is the Poisson's ration (0.15), $a$ is the radius of the contact area and $l$ is the radius of the relative stiffness.