29.4. Combination of stresses

Summer, mid-day: The critical stress is for edge region given by σ = σ + σ σ • critical e te − f

During the summer, particularly in the mid-day heat, the edge of the pavement experiences significant stress. This stress is quantified by the equation where the total stress σ critical in the edge region is the sum of three types of stresses: the elastic stress (σ e), warping stress (σ t), and frictional stress (σ f). Each of these components contributes to the overall stress experienced by the pavement, especially with rising temperatures leading to expansion and potential bending.

Think of a metal rod left in the sun. As the temperature rises, the rod expands. Similarly, when the pavement is subjected to high temperatures, it expands, leading to stresses at the edges where the material meets resistance from the sub-grade below. Just like a stretched rubber band, if the pavement cannot expand adequately, it can crack or warp.

Winter, mid-day: The critical combination of stress is for the edge region given by σ = σ + σ + σ • critical e te f

In winter, the pavement experiences a combination of stresses at mid-day, particularly at the edges. The total stress σ critical is again composed of the elastic stress (σ e), warping stress (σ t), and frictional stress (σ f). Here, the air temperature is lower, which causes thermal contraction of the concrete slab. The graphical representation often shows that even in winter, the edge of the slab remains vulnerable to loading stresses combined with these thermal effects, which can lead to premature failure if not accounted for.

Imagine a wooden board that shrinks as it gets cold. If it’s nailed to the frame, the nails can either pull out or the board can crack. Pavement behaves similarly; when it cools down, it contracts, creating stress along its edges which can impair its integrity unless designed to accommodate these stresses.

Mid-nights: The critical combination of stress is for the corner region given by σ = σ • critical c tc

At midnight, the critical stress is assessed at the corner of the pavement slab. The equation σ critical incorporates the thermal contraction and stresses experienced at the corners, which are particularly sensitive spots due to their geometry. Here, unlike the edge or interior, the corner endures different load dispersions leading to varying magnitudes of stresses that must be calculated to maintain the pavement's structural integrity.

Consider the corners of a fabric when pulling it tight. The tension at the corners is much greater than along the flat sections, as the fabric tries to gather at the corners. Similarly, corners of pavements face concentrated stress due to curvature and loading patterns, requiring thorough evaluation during design to prevent cracking or failure.

--