Comparison of Beam Depths for Stiffened Slabs on Shrink-Swell Soils Using WRI, PTI 2004 and AS 2870

The most common foundation for light structures founded on shrink-swell soils is the stiffened slab on grade. The beam depth is an intrinsic design parameter for this type of foundation, it usually ranges between 0.6 and 1.2 m with common beam spacing of 3 to 6 m placed in both directions. The following methods are among the most common methods used to calculate the beam depth, spacing, and reinforcement needed for a safe and serviceable foundation: 1) BRAB Method (1968); 2) WRI Method (1980, 1996); 3) PTI Method (1996); 4) AS 2870 (1996); 5) PTI Method (2004). WRI and PTI Method (2004) are the most recently developed method in the USA while the AS 2870 is the most recent version of the Australian Standards. For the same input design data, applying these three design methods may result in different beam depths. In order to compare these methods, 27 cases are designed. They include three simple rectangular stiffened slabs subjected to three different weather patterns, built on three different shrink-swell soils, and loaded with a uniform pressure and perimeter line load. The resulting beam depths using the WRI, PTI 2004 and the AS 2870 methods in different soil and weather conditions are also presented and discussed.