COMPARATIVE INVESTIGATION OF TWO DESIGN METHODS FOR SLAB-ON-GRADE FOUNDATIONS SUBJECTED TO CONCENTRATED LOADS

Abstract

The concrete slab-on-grade is a type of shallow foundation commonly used in warehouse and other industrial facilities. The slab is constructed in formwork set into the ground with concrete poured directly onto compacted subgrade. Slab-on-grade foundations designed by the traditional linear elastic method may have overly conservative slab thicknesses. As the slab-on-grade foundation can account for up to 15% of construction costs for the projects in which they are employed, reduction in the slab thickness can result in significant cost savings. An alternate design method (Shentu et al. 1997) has been proposed but has not been widely accepted due to lack of confidence in its correlation with test results. The objectives of this study were to experimentally define a reasonable factor of safety for the Shentu method and compare with the traditional design method. Test slabs of varying thicknesses, 5 ft by 5 ft in area, were built on top of compacted local soils and aggregates inside a testing box and tested to failure under static loads to simulate storage rack post loads; companion slabs were constructed on top of compacted soils and aggregates and field-tested. Concrete mixes with and without fibers were used in the study. Factors of safety were determined. Test results indicate that the Shentu method is too liberal in its computations while the traditional design method is overly conservative.