360R-06 Design of Slabs-on-Ground
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| 9.2—Definitions
Selected terms and expressions that appear in Chapter 9 are defined and explained. allowable differential deflection—the amount of slab deflection that can be tolerated by the type of superstructure supported by the slab or equipment operating on the slab. differential deflection distance—the total slab length may not be the proper distance over which to evaluate the acceptability of the expected differential deflection. Analysis of the locations of maximum and minimum deflections shows that several such locations may occur in longer (or wider) slabs; that is, the slabs experience multimodal bending (Thompson and Anderson 1968). All such bending, however, occurred within a distance of 6 β from the edge of the slab. Using a length of L or 6 β, whichever is smaller, when deter- mining the allowable differential deflection, will limit the deflection to an acceptable amount, and this length is called the differential deflection distance. differential soil movement y m —this is the expected vertical movement of the perimeter soil due to type and amount of clay mineral, its initial wetness, the depth of the zone within which the moisture varies, and other factors (PTI 2004). The differential soil movement will often be greater than the allowable deflection. edge moisture variation distance e m —also known as the edge moisture penetration distance, e m is the distance measured inward from the edge of the slab over which the moisture content of the soil varies. An increasing moisture content at increasing distances inside the slab perimeter is indicative of a center lift condition, whereas a decreasing moisture content indicates an edge lift condition. lift conditions—several terms refer to the shape of a slab or the stresses generated within a slab during the transition period from the as-cast shape to the intermediate or long- term shape. If the moisture content of the soil beneath the slab changes after construction of the slab, it will distort into either a center lift condition (also termed “center heave” and “doming”) or an edge lift condition (also called “edge heave” and “dishing”). The center lift condition is a long- term condition and occurs either when the soil beneath the interior of the slab becomes wetter and expands, when the soil around the perimeter of the slab dries and shrinks, or a |